In this article: We'll review our best marine and boat subwoofer picks for your marine application. We'll break them out by brand, cost including a budget pick and provide quick reviews, product photos and price comparisons to help you save money.
Are you looking for a more bass from your boat's stereo? A top-notch marine subwoofer for your boat, in our opinion, is a necessity and really the only way you’ll get the deep bass you want while you're on the water. Especially if it’s in an open-boat application. You may think an aftermarket subwoofer is just for seasoned audiophiles, but they’re for anybody who just wants more out of their marine or boat’s stereo.
But the best subwoofers for boats don’t just add extra bass, they’ll make your other speakers sound better too. Better sound from your speakers is achieved by relieving them of bass duty. Instead of pumping out the highs, mids, and lows all at once, your subwoofer can take care of the deep lows while your other speakers deliver crisper, clearer high and mid-range sound. It’ll help you get more volume out of your speakers, and obviously added bass.
If you’re just getting started on creating your dream marine audio setup, read some of our other reviews. Check out our lists of best marine stereos and best marine speakers and find what’s right for you. A good marine amplifier can go a long way in powering your system too, especially with a subwoofer.
Regardless of whether you’re looking for the most powerful bass money can buy or just want a little extra kick in your boat chances are you’ll find the best subwoofer for your boat on our list.
Best Marine Subwoofers
1. Best Overall Pick: JL Audio M7 Series
JL Audio M7 Series Marine Subwoofer Review
JL Audio makes some of the best subwoofers on the market. But, when it comes to getting big-time bass on your boat, you used to be stuck installing subs designed for your car. Obviously, that’s not the ideal solution when you’re in hot, damp and salty environments. Although, many people still put the W6 and W7 series in their boats. Now, JL Audio has brought ground-pounding subs to you, complete with the latest advances in waterproofing and sealing. We did a first look on the 12” version of this speaker, and before you know it, we will have a performance review posted up so you can get an idea about why we love this series so much.
The specs on the W7 are off the charts. These subs are bigger, stronger, and more powerful than basically anything on the market, but you are going to pay a premium price. Some of the basics: an all-new frame and spider are combined with 2”, 4 ohm voice coils and a specially formulated, UV-resistant surround. It’s got LED lighting that shines through the cone you can set to one of seven different colors. Peak power and RMS power ratings are not only accurate, but exceed virtually anything out there. To put it as simply as possible, this is THE subwoofer you need, especially in a Free-Air application.
The M7 is available with six different grills in two different colors to fit perfectly with your boat. The sub is designed as an infinite baffle sub, and JL Audio cautions that extra attention to the mounting surface is essential to get proper performance.
Key Features
- 4-ohm resistance for all sizes
- “Transflective” RGB Lighting, 7 colors
- White and Titanium grills
- Ideal for Free-Air and Infinite Baffle
- Uses Amplifiers rated 75W-600W RMS
- Two Inch Voice Coil
- 600 watts RMS
Reasons to Buy
- Thundering bass
- Superior waterproofing
- Oversized cone
Reasons Not to Buy
- Expensive
- Requires a considerable amount of power
- A little bigger than your traditional 12″ cutout
M7-12IB-S-GMTi-i-4
Size: 12″
Type: Free Air/Infinite Baffle
Impedance: 4Ω
Power Handling: 600 RMS, 1200W PEAK
Price Comparison
M7-12IB-S-GwGw-i-4
Size: 12″
Type: Free Air/Infinite Baffle
Impedance: 4Ω
Power Handling: 600 RMS, 1200W PEAK
Price Comparison
M7-12IB-C-GwGw-i-4
Size: 12″
Type: Free Air/Infinite Baffle
Impedance: 4Ω
Power Handling: 600 RMS, 1200W PEAK
Price Comparison
2. Wet Sounds REVO Series
Wet Sounds REVO Series Marine Subwoofer Review
Wet Sounds does a few things with their products to really set them apart from others. The speakers, subs, and head units from Wet Sounds are some of the most well-protected from salt spray, fog, and UV rays, which is very important for nautical audio equipment. They follow up durable equipment with industry-leading tech to help you build the ideal dynamic sound environment onboard.
The REVO-series subwoofers are available in three configurations, numerous sizes, and impedance ratings. For boaters looking to absolutely bump the beach, the REVO-series has the power and performance you are looking for. Revo subwoofers are designed for free-air applications and enclosures, with the top-of-the-line Revo-XXX subs providing absurd power handling and bass response, comparable to a professional sound competition subwoofer.
Both the free-air and enclosure subwoofers feature similar specs- the ability to handle 400 to 500 watts RMS from the 10” & 12” subs, 2 ohm and 4 ohm setups to tailor to your system, and fully sealed, waterproof motors and magnets. Santoprene is featured not only on the surround, but also on the spider for long-lasting resistance to the elements. The REVO-series is tough to beat, and loading up your watercraft with these subs will ensure you have the beats with you season after season.
Key Features:
- Revo XXX, HP, FA (Competition, enclosure, free-air versions)
- 10”, 12”, and 15” models
- Power handling from 400 watts RMS to 2,000 watts RMS
- Santoprene surround and spider
- Nylas composite frame
- Stainless steel terminals (gold plated on XXX models)
- Two and four ohm resistance options
- Sealed motor and magnet
- Injection molded composite cone
- Grills and LED lighting sold separately
Reasons to Buy
- One of the most durable subwoofer lines on the market
- Exceptional power handling abilities
- Lots of options
Reasons Not to Buy
- Lack of included grills and lighting at the price point is questionable
REVO 8 FA S4-W
Size: 8″
Type: Free Air/ Infinite Baffle
Impedance: 4Ω
Power Handling: 150W RMS, 300W PEAK
Price Comparison
REVO 8 FA S4-B
Size: 8″
Type: Free Air/ Infinite Baffle
Impedance: 4Ω
Power Handling: 150W RMS, 300W PEAK
Price Comparison
REVO 10 FA S2-W
Size: 10″
Type: Free Air/ Infinite Baffle
Impedance: 2Ω
Power Handling: 300W RMS, 600W PEAK
Price Comparison
REVO 10 FA S2-B
Size: 10″
Type: Free Air/ Infinite Baffle
Impedance: 2Ω
Power Handling: 300W RMS, 600W PEAK
Price Comparison
REVO 10 FA S4-W
Size: 10″
Type: Free Air/ Infinite Baffle
Impedance: 4Ω
Power Handling: 300W RMS, 600W PEAK
Price Comparison
REVO 10 FA S4-B
Size: 10″
Type: Free Air/ Infinite Baffle
Impedance: 4Ω
Power Handling: 300W RMS, 600W PEAK
Price Comparison
REVO 12 FA S2-W
Size: 12″
Type: Free Air/ Infinite Baffle
Impedance: 2Ω
Power Handling: 400W RMS, 800W PEAK
Price Comparison
REVO 12 FA S2-B
Size: 12″
Type: Free Air/ Infinite Baffle
Impedance: 4Ω
Power Handling: 400W RMS, 800W PEAK
Price Comparison
REVO 12 FA S4-W
Size: 12″
Type: Free Air/ Infinite Baffle
Impedance: 4Ω
Power Handling: 400W RMS, 800W PEAK
Price Comparison
REVO 12 FA S4-B
Size: 12″
Type: Free Air/ Infinite Baffle
Impedance: 4Ω
Power Handling: 400W RMS, 800W PEAK
Price Comparison
REVO 10 HP S4-B
Size: 10″
Type: Enclosure
Impedance: 4Ω
Power Handling: 400W RMS, 800W PEAK
Price Comparison
REVO 15 XXX V4-B
Size: 12″
Type: Enclosure
Impedance: 4Ω
Power Handling: 2000W RMS, 4000W PEAK
Price Comparison
3. Kicker KM Series
Kicker KM Series Marine Subwoofer Review
You know Kicker is one of our favorite brands to install. We write about their products all the time and recommend them to our own friends and family (see our KMF Series Review and Lightning Speedboat Stereo Upgrade). The company simply builds great quality audio components that work amazingly well. When you buy a subwoofer for your boat, you need to know it’ll hold up to serious abuse, including spray, salt, fog, and getting cranked up. The KM-series doesn’t disappoint.
Kicker starts out with a proven design- one they designed from the ground up just for this series. The UV-treated polypropylene woofer features a Santoprene surround for long-term durability in harsh environments- like when that booty shakin’ song comes on and you gotta turn it all the way up. The motor is fully sealed from the elements for peace of mind you can’t get from non-marine grade speakers.
Kicker offers these subs with different resistances and both enclosure and free-air designs. A free-air sub can be particularly wonderful on boats that lack the space for an enclosure, while still producing wave-making bass.
Key Features
- Subwoofers available in 10” & 12”
- Models for free-air or enclosure applications
- Two or four ohm resistance
- 1” titanium voice coil
- UV-treated woofer with Santoprene surround
- 175 watts RMS, 300 Peak
- 30-500 Hz frequency response
- Optional LED light rings available in 20 colors and 19 modes
Reasons to Buy
- Tough and durable marine-grade sub, a first from one of our favorite companies
- Some models include multiple grill covers to match your interior
Reasons Not to Buy
- LED lighting grille is not included
KMF102
Size: 10″
Type: Free Air/Infinite Baffle
Impedance: 2Ω
Power Handling: 175W RMS, 300W PEAK
Price Comparison
KMF104
Size: 10″
Type: Free Air/Infinite Baffle
Impedance: 4Ω
Power Handling: 175W RMS, 300W PEAK
Price Comparison
KMF122
Size: 12″
Type: Free Air/Infinite Baffle
Impedance: 2Ω
Power Handling: 175W RMS, 350W PEAK
Price Comparison
KMF124
Size: 12″
Type: Free Air/Infinite Baffle
Impedance: 4Ω
Power Handling: 175W RMS, 350W PEAK
Price Comparison
KM102
Size: 10″
Type: Enclosure
Impedance: 2Ω
Power Handling: 175W RMS, 350W PEAK
Price Comparison
KM104
Size: 10″
Type: Enclosure
Impedance: 4Ω
Power Handling: 175W RMS, 350W PEAK
Price Comparison
KM122
Size: 12″
Type: Enclosure
Impedance: 2Ω
Power Handling: 175W RMS, 350W PEAK
Price Comparison
KM124
Size: 12″
Type: Enclosure
Impedance: 4Ω
Power Handling: 175W RMS, 350W PEAK
Price Comparison
4. Rockford Fosgate M2 Series
Rockford Fosgate M2 Series Marine Subwoofer Review
You may (or may not) know Rockford Fosgate more for the company’s incredibly tough and powerful car and home audio equipment. But with the M2 series marine subs, the things you love about RF in your car you can also bring on the water. The M2-series is Rockford's latest flagship marine-grade subwoofer, released in late 2019. It's specially designed just for marine applications, and features three sizes, both enclosure and free-air set ups, and several resistance ratings to match your system.
All of the M2-series subwoofers feature dual voice coils for superior sound without distortion. Rockford Fosgate went an extra step to make sure consumers got the best bass for the buck with the M2-series by certifying with numerous agencies. The subs are IPX6-rated for protection from consistent water and moisture that's typical while you're on the water, and ASTM-certified to resist salt and fog for 500 continuous hours. It's also Klippel certified for power, sound, and efficiency. They really went above and beyond to make sure you get the best sub for your boat or marine application.
Many marine subs feature LED lighting, and some of them look pretty good, but if you really want great visuals to go along with bone-shaking bass, the RF MX-series has one of the most versatile app-controlled lighting systems out there. The Color Optix lighting package, along with the appropriate controller, provides near infinite customizable light shows to really crank up the party atmosphere.
Key Features
- Free-air and enclosure models
- 10”, & 12” models
- Two and four ohm resistance, switchable to eight ohm
- 150 watt to 400 watt RMS depending on size
- Dual voice coils
- Element Ready protection from dust, UV, salt, spray, fog
- IPX6-rated for waterproofing
- VAST technology for 25% larger effective area
Reasons to Buy
- Flexible lighting features
- Extensive certifications for quality, durability and sound
Reasons Not to Buy
- Power handling is lower than some of it's competitors
M2D2-10IB
Size: 10″
Type: Free Air/Infinite Baffle
Impedance: 1Ω or 4Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
M2D4-10IB
Size: 10″
Type: Free Air/Infinite Baffle
Impedance: 2Ω or 8Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
M2D2-10I
Size: 10″
Type: Free Air/Infinite Baffle
Impedance: 1Ω or 4Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
M2D4-10I
Size: 10″
Type: Free Air/Infinite Baffle
Impedance: 2Ω or 8Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
M2D2-10SB
Size: 10″
Type: Enclosed
Impedance: 1Ω or 4Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
M2D4-10SB
Size: 10″
Type: Enclosed
Impedance: 2Ω or 8Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
M2D2-10S
Size: 10″
Type: Enclosed
Impedance: 1Ω or 4Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
M2D4-10S
Size: 10″
Type: Enclosed
Impedance: 2Ω or 8Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
M2D2-12IB
Size: 12″
Type: Free Air/Infinite Baffle
Impedance: 1Ω or 4Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
M2D4-12IB
Size: 12″
Type: Free Air/Infinite Baffle
Impedance: 2Ω or 8Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
M2D2-12I
Size: 12″
Type: Free Air/Infinite Baffle
Impedance: 1Ω or 4Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
M2D4-12I
Size: 12″
Type: Free Air/Infinite Baffle
Impedance: 2Ω or 8Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
M2D2-12SB
Size: 12″
Type: Enclosed
Impedance: 1Ω or 4Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
M2D4-12SB
Size: 12″
Type: Enclosed
Impedance: 2Ω or 8Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
M2D2-12S
Size: 12″
Type: Enclosed
Impedance: 1Ω or 4Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
M2D4-12S
Size: 12″
Type: Enclosed
Impedance: 2Ω or 8Ω
Power Handling: 400W RMS, 1600W PEAK
Price Comparison
5. Clarion Marine CMSP Series
Clarion Marine CMSP Series Subwoofer Review
Clarion has been in the marine business for a long time. Their newest subwoofers, the CMSP series, are available in 10” diameter infinite baffle design. The CMSP-series of subwoofers includes a two ohm and a four ohm variant. They are fully marinized for years of abuse on your boat. Clarion Marine even went the extra step to seal the speaker connectors to prevent corrosion in wet environments. A mica-filled polypropylene woofer ensures water-resistance, while the Santoprene surround will withstand UV rays, salt, and fog.
The CMSP is a ground-up innovation that was just released in 2020. For Clarion Marine, the design of the speaker is a new direction for the company. It has a long-excursion design that provides excellent low frequencies without distortion. Clarion also designed a special polymer basket and marine-grade synthetic spider to enhance long-term performance and help provide deep bass.
The CMSP subs include RGB lighting that can be set to one of seven colors. An optional light controller allows you to set the lights to your music or add custom effects. The sub includes a wiring harness to connect the lights to a 12V power source. The only downsides to this series is that it doesn't come in a 12″ model and the grilles are sold separately. You can find the grilles on clarion's website here.
Key Features
- 10” free-air subwoofer
- Two or four ohm variants
- 250 watts RMS power handling, 500 watts peak
- Injection-molded polypropylene woofer
- Santoprene surround
- Synthetic spider
- Polymer marine-grade basket
- Built-in RGB LED lighting
Reasons to Buy
- Durable build quality that meets or exceeds standards
- Excellent lighting options
Reasons Not to Buy
- Does not include grills
- Limited information about specifications available online at the time of writing this list
- Only offered in 10″ model
CMSP-101RGB-2
Size: 10″
Type: Free Air/Infinite Baffle
Impedance: 2Ω
Power Handling: 250W RMS, 500W PEAK
Price Comparison
CMSP-101RGB-4
Size: 10″
Type: Free Air/Infinite Baffle
Impedance: 4Ω
Power Handling: 250W RMS, 500W PEAK
Price Comparison
6. Infinity Reference 1022 ML Series
Infinity Reference 1022 MLT Series Marine Subwoofer Review
The Infinity Reference series are some of the best speakers and subwoofers we've ever heard in car audio. Understandably, we were quite excited when Infinity introduced a marinized version of their Reference series back in 2018. The 1022 ML-series are 10” subwoofers that produce some of the cleanest and most accurate bass tones possible. Infinity uses a rigorous testing process to fine-tune their speakers, giving the consumer unparalleled consistency. This is of particular importance on your boat, where out-of-sync tones are going to make the bass sound muddy.
The 1022 ML-series are best used as free air subs. Their sealed motor and fully marine-grade components tend to act like a baffle so you don’t need a massive box. It’s not recommended for small boxes, though. The series comes in either white or titanium, and features built-in LED lighting with seven colors. As you would expect from Infinity, the grills and lighting produce an exceptionally attractive looking speaker.
The sub uses a one-piece polymer basket and a rubber surround to pump the bass. Infinity mounts a bridged tweeter into the center of the cone, which helps balance the bass and provides a waterproof seal. The sub has an IPX5 rating so it’ll take salt, spray, fog, even the occasional wave without skipping a beat. The only thing that's missing from Infinity is a 12″ subwoofer. As of today they only come in 10″.
Key Features
- 10” Subwoofer in two colors
- 250 Watts RMS
- Four ohm resistance
- RGB LED lighting, seven colors
- 25-500 Hz frequency response
- One-piece polymer basket
- IPX5-rated waterproof
Reasons to Buy
- Attractive and durable marine subwoofer
- Clear bass tones even at high volume
Reasons Not to Buy
- Limited options in terms of size, color and power
1022MLT
Size: 10″
Type: Free Air/Infinite Baffle
Impedance: 4Ω
Power Handling: 250W RMS, 750W PEAK
Price Comparison
1022MLW
Size: 10″
Type: Free Air/Infinite Baffle
Impedance: 4Ω
Power Handling: 250W RMS, 750W PEAK
Price Comparison
7. Budget Pick: Polk Audio DB+ Series
Polk Audio DB+ Series Marine Subwoofer Review
One of the biggest challenges in building a great system for your boat is, of course, affording it. With some subs costing $500-$1,000 each, your on-the-water stereo can quickly exceed the value of your boat. Polk Audio takes the financial fret out of the equation with the DB+ series of marine-grade subwoofers. Priced around $100 for even the largest and most powerful sub in the series, Polk brings affordability to that big system build you want.
Inexpensive equipment is great, but it’s gotta work, too. No one wants to deal with speakers that fail for no reason or sound horrible, and Polk made sure these subs won’t let you down. The series is available in 8”, 10”, & 12” sizes with both single and dual voice coils. Excellent frequency response across the range and better than expected RMS power handling make these the best choice for budget boat builds.
Polk saves you money by keeping things simple. There is no LED lighting, no color options for cones and grills, and not a lot in the way of complexity. Instead of fancy options, Polk just brings a solid, dependable, and well-engineered subwoofer that gets the job done at an unbeatable price point.
Key Features
- 8”, 10”, & 12” models
- Single and dual voice coils
- Four ohm resistance
- IP56-rated for dust and moisture resistance
- 250 watt -370 watt RMS depending on size
- Designed for small enclosures
Reasons to Buy
- Price point
- Good power and durability
- Shallow/compact design
- Variety of sizes (the only 8″ subwoofer on this list)
Reasons Not to Buy
- Basic tech will get good bass, but not mind-blowing
- Simple design that's not as stylish as others
DB842SVC
Size: 8″
Type: Enclosed
Impedance: 4Ω
Power Handling: 250W RMS, 750W PEAK
Price Comparison
DB842DVC
Size: 8″
Type: Enclosed
Impedance: 4Ω
Power Handling: 250W RMS, 750W PEAK
Price Comparison
DB1042SVC
Size: 10″
Type: Enclosed
Impedance: 4Ω
Power Handling: 350W RMS, 1050W PEAK
Price Comparison
DB1042DVC
Size: 10″
Type: Enclosed
Impedance: 4Ω
Power Handling: 350W RMS, 1050W PEAK
Price Comparison
DB1242SVC
Size: 12″
Type: Enclosed
Impedance: 4Ω
Power Handling: 370W RMS, 1110W PEAK
Price Comparison
DB1242DVC
Size: 12″
Type: Enclosed
Impedance: 4Ω
Power Handling: 370W RMS, 1110W PEAK
Price Comparison
Looking for more boat stereo products? Check out these lists!
Best Boat Subwoofers: What to Look For
The terminology you need to know for boat subwoofers is pretty similar to what you should look for in any subwoofer. We’ll go over those specs and what they mean to make you an expert.
- RMS Power Rating – We reference RMS power ratings a lot in this list. It’s not something you hear a lot about from the manufacturer and we’ll get into why that is in a minute. RMS stands for “root mean square” which is a mathematical measurement of the best value of a waveform. What it means in plain English is the recommended power rating. RMS is the power level at which you can listen to music through a sub for a sustained period of time. This power level is measured in watts. This is one of the main specs you should be looking for when shopping for the best marine subwoofer. Something to keep in mind – each manufacturer calculates RMS a little differently. If you’re concerned about it being able to keep up with your amp, dig in and do some extra research on how the manufacturers you like measure their RMS.
- Peak Power Rating – Peak power is where the bragging rights lie for subwoofers. It’s the number you’ll see marketed and plastered in a big font on the packaging. While it’s not as important as RMS, it’s a bigger number so it’s the one manufacturers like to throw around. Since most people don’t know the difference between peak and RMS, they figure the bigger the number, the better. While it’s true that a higher peak power means it can go louder without blowing up, it isn’t as important as RMS. A subwoofer can only handle input at its peak power for moments at a time, not at that high of a sustained volume. If there’s a loud part of a song that goes higher than the RMS, the peak power takes care of it. When looking at the peak power rating of a sub, make sure it matches up with the peak power of your head unit or amplifier. If you feed a sub more watts than it can handle, you’ll have problems.
- Impedance – Impedance isn’t a huge deal, but it’s still worth noting and understanding. You’re going to see measurements of ohms in each subwoofer description. Ohm is a measurement of electrical resistance which is basically what speaker impedance is. The subwoofer acts like a big resistor and the lower the ohms, the more power it can handle from an amplifier. Lower ohms ratings are often found on high-end products like the ones we’ve reviewed here. The best subwoofer for boats usually has an impedance rating of 4 ohms or lower.
- Size – This might seem obvious, but sometimes the size of a subwoofer is overlooked. 10-inches is the most common size for marine subwoofers, but there are varying sizes for different applications. Bigger doesn’t always mean better. There’s an 8-inch sub on our list that would be great for a smaller boat or if you just want it to be less noticeable.
- Mounting – Like size, mounting is important to keep in mind when thinking about where you’re going to put your sub. While the diameter of the actual speaker might be uniform, shapes and sizes can vary greatly between different models. Some are deeper than others. They all have different mounting brackets. Some are intended to go into special enclosures. When you find the best boat subwoofer for you, make sure you do some measuring and have an idea of how you’ll mount it. You don’t want to get it and then figure out you can’t install it where you wanted to.
- Marinization – What sets the best marine subwoofers apart from normal ones is the marinization. A car subwoofer doesn’t need to be able to withstand the elements like a marine one. Marinization doesn’t just mean water resistance. It also needs to be able to stand up to salt, UV rays, and maybe sand. They’re marinized not only for durability, but to maintain high sound quality with the right protection on the right components. Take your environment in consideration when choosing your sub.
- Free Air/Infinite Baffle vs Sealed Enclosure – We also reference what's called a ‘Free Air/Infinite Baffle' subwoofer as the “type” in this article. Many of the subwoofers that are designed for a marine application happen to be Free Air/Infinite Baffle. Be sure you understand the application that you're putting your subwoofer into. We don't recommend putting a Free Air/Infinite Baffle subwoofer into a small enclosure, unless it's designed for it. Similarly, you don't want to put a subwoofer that's designed for a sealed enclosure into a free air setting. It'll significantly degrade the sound quality. Check out our Free Air/Infinite Baffle Defined article to learn more.
18″inch