Boat Paint Calculator
Work out how much bottom paint, topside enamel, primer, or bilge paint your project needs. Enter your boat length and beam (or your measured area), pick a hull type, and get gallons plus product recommendations from our shelf.
How the paint estimate works
For bottom jobs the calculator estimates your wetted area from length and beam with a hull-type coefficient, matching the industry rule of waterline length times beam times 0.75 to 0.77 for planing and fin-keel hulls (higher for displacement hulls). Pontoons are different: the painted area is the tube surface down to the waterline, so the calculator uses tube girth times length and ignores beam. Gallons come from area times coats, divided by the paint's coverage rate, plus a 10 percent waste factor.
- Antifouling bottom paint. Roughly 400 sq ft per gallon per coat. Two coats is the standard system, with a third on leading edges and the waterline.
- Barrier coat. Around 250 sq ft per gallon. Barrier epoxy goes on before antifouling on a bare or blistered hull.
- Topside and enamel. About 350 sq ft per gallon. Measure your actual surfaces; topsides, transom, and deck areas vary too much to estimate from length alone.
- Primer and bilge paint. 300 to 350 sq ft per gallon, usually one to two coats over a cleaned, sanded surface.
Boat paint FAQ
How much bottom paint do I need for a 30 foot boat?
A typical 30 ft planing powerboat with a 10 ft beam has about 210 sq ft of bottom. Two coats of antifouling at 400 sq ft per gallon works out to roughly 1.2 gallons, so buy 2 gallons. Run your own numbers above for an exact estimate.
How many coats of antifouling paint should I apply?
Two full coats is the standard system for ablative and hard antifouling, with an extra pass on the waterline, leading edges, and rudder where the paint wears fastest. One coat rarely lasts a season.
What bottom paint is safe for a pontoon boat?
Aluminum tubes need copper-free antifouling. Copper-based paint in contact with aluminum sets up galvanic corrosion that eats the tubes. Pick the pontoon hull option in the calculator and it only recommends copper-free formulas.
How do I measure the bottom area of my boat?
The standard estimate is waterline length times beam times a hull factor: about 0.75 to 0.77 for planing hulls and fin-keel sailboats, and up to 0.9 for full-displacement hulls. For a precise number, measure your hull below the waterline in sections.
Does the estimate include a waste factor?
Yes. The calculator adds 10 percent for roller and tray losses, overlap, and touch-up. Coverage also varies by surface roughness, so a first coat over bare or sanded gelcoat runs heavier than the numbers on the can.