UseCalcPro
Home
MathFinanceHealthConstructionAutoPetsGardenCraftsFood & BrewingToolsSportsMarineEducationTravel
Blog
  1. Home
  2. Marine

Boat Paint Calculator

Estimate antifouling paint from hull dimensions

Units

Total Paint Needed

1.89

gallons (2 gal)

Per Coat

0.95 gal

Total Cost

$341

Hull Surface

Wetted Surface Area

332 sq ft

Cost per Coat

$170

Cost by Paint Type

Ablative$341
Hard$332
Copper-Free$449
Racing$368

Bottom Paint Coverage by Type

Paint TypeCoverage (sq ft/gal)Avg Price/GalBest For
Ablative350$180Seasonal boaters
Hard Modified Epoxy400$200Year-round in water
Copper-Free325$220Aluminum hulls
Racing / Thin-Film450$250Speed-focused

What You'll Need

Star Brite Ultimate Aluminum Cleaner & Restorer 64oz

$18-$254.5
View on Amazon

3M Marine Adhesive Sealant 5200 Fast Cure White 3oz

$14-$204.5
View on Amazon

Shoreline Marine Bilge Pump 600 GPH 12V

$15-$254.3
View on Amazon

Star Brite Ultimate Aluminum Cleaner & Restorer 64oz

$18-$254.5
View on Amazon

3M Marine Adhesive Sealant 5200 Fast Cure White 3oz

$14-$204.5
View on Amazon

Shoreline Marine Bilge Pump 600 GPH 12V

$15-$254.3
View on Amazon

As an Amazon Associate, we earn from qualifying purchases.

Frequently Asked Questions

Q

How do I calculate wetted surface area for bottom paint?

The wetted surface area formula is SA = LOA × (Beam + Draft) × Hull Factor. The hull factor accounts for hull shape: 0.85 for powerboats, 0.75 for fin-keel sailboats, and 0.90 for catamarans.

  • Powerboat hull factor: 0.85 — moderate deadrise shape
  • Sailboat fin keel factor: 0.75 — narrow underbody with deep keel
  • Sailboat full keel factor: 0.85 — similar to powerboat coverage
  • Catamaran factor: 0.90 — two narrow hulls with more surface per foot
  • A 30 ft powerboat with 10 ft beam and 3 ft draft: 30 × 13 × 0.85 = 332 sq ft
Boat Size (LOA)Hull TypeWetted SA (sq ft)Gallons (2 coats)
22 ftPowerboat1681.0
30 ftPowerboat3321.9
36 ftSailboat3041.7
40 ftCatamaran5403.1
Q

How many coats of bottom paint does a boat need?

Most boats need 2 coats of antifouling paint for adequate protection. Boats in warm, high-fouling waters may need 3 coats. A single coat is acceptable for touch-ups or freshwater-only boats.

  • 1 coat: seasonal touch-up or low-fouling freshwater areas
  • 2 coats: standard for most recreational boats in saltwater
  • 3 coats: tropical waters, boats left in the water year-round
  • Waterline area gets extra wear — apply an additional stripe coat
  • New gelcoat needs a compatible primer before antifouling paint
Q

What type of bottom paint should I use?

Ablative paint is best for seasonal boaters because it wears away evenly. Hard modified epoxy suits boats kept in the water year-round. Copper-free paint is required for aluminum hulls. Racing paint provides the smoothest finish.

  • Ablative: self-polishing, good for haul-out storage, ~350 sq ft/gal coverage
  • Hard epoxy: durable, best for year-round wet storage, ~400 sq ft/gal
  • Copper-free: safe for aluminum hulls, more expensive at ~$220/gal
  • Racing thin-film: smoothest finish, lowest drag, ~450 sq ft/gal but $250/gal
  • Never apply copper-based paint directly over copper-free or vice versa
Paint TypeCoveragePrice/GalBest For
Ablative350 sq ft$180Seasonal boats
Hard Epoxy400 sq ft$200Year-round
Copper-Free325 sq ft$220Aluminum hulls
Racing450 sq ft$250Performance
Q

How much does it cost to bottom paint a boat?

DIY bottom painting costs $150–$500 in materials for most recreational boats. Professional bottom painting runs $15–$30 per foot of boat length plus materials, so a 30 ft boat typically costs $800–$1,500 total at a boatyard.

  • DIY materials for 25 ft boat: ~$180–$360 (1–2 gallons of paint)
  • DIY materials for 35 ft boat: ~$360–$700 (2–4 gallons)
  • Boatyard labor: $15–$30 per foot depending on region
  • Haul-out fee: $8–$15 per foot additional
  • Prep work (sanding, cleaning) adds 50–100% labor time
Q

How long does bottom paint last on a boat?

Ablative bottom paint lasts 1–2 seasons depending on use and water temperature. Hard epoxy paint can last 2–3 seasons with proper application. Racing paint typically lasts only one season before needing reapplication.

  • Ablative: 12–24 months, wears with use and water flow
  • Hard epoxy: 18–36 months, builds up with each application
  • Racing: 6–12 months, thin-film wears quickly
  • Warm tropical waters reduce paint life by 30–50%
  • Boats used weekly last longer than boats sitting still (ablative type)

Example Calculations

130 ft Powerboat with Ablative Paint

Inputs

LOA30 ft
Beam10 ft
Draft3 ft
Hull TypePowerboat (0.85)
Paint TypeAblative (350 sq ft/gal)
Coats2

Result

Total Paint1.89 gallons
Wetted Surface Area332 sq ft
Per Coat0.95 gal
Total Cost$341

SA = 30 × (10 + 3) × 0.85 = 331.5 sq ft. Per coat = 331.5 / 350 = 0.95 gal. Total = 0.95 × 2 = 1.89 gal. Cost = 1.89 × $180 = $341.

236 ft Sailboat (Fin Keel) with Hard Epoxy

Inputs

LOA36 ft
Beam11 ft
Draft6 ft
Hull TypeSailboat fin keel (0.75)
Paint TypeHard Modified Epoxy (400 sq ft/gal)
Coats2

Result

Total Paint2.30 gallons
Wetted Surface Area459 sq ft
Per Coat1.15 gal
Total Cost$459

SA = 36 × (11 + 6) × 0.75 = 459 sq ft. Per coat = 459 / 400 = 1.15 gal. Total = 1.15 × 2 = 2.30 gal. Cost = 2.30 × $200 = $459.

Formulas Used

Wetted Surface Area

SA = LOA × (Beam + Draft) × Hull Factor

Estimates the underwater hull area that needs antifouling paint.

Where:

LOA= Length overall of the boat in feet
Beam= Maximum beam (width) in feet
Draft= Draft depth below waterline in feet
Hull Factor= Shape correction (0.75–0.90 depending on hull type)

Paint Required

Gallons = (SA / Coverage) × Coats

Calculates total paint volume from surface area, coverage rate, and number of coats.

Where:

SA= Wetted surface area in square feet
Coverage= Paint coverage rate in sq ft per gallon (325–450)
Coats= Number of coats to apply (1–3)

Understanding Boat Bottom Paint Coverage

Bottom paint (antifouling paint) prevents marine growth like barnacles, algae, and slime from attaching to your hull. Without it, fouling can reduce speed by 10–20%, increase fuel consumption by 30% or more, and damage gelcoat over time. Choosing the right type and amount is essential for every boat owner.

The wetted surface area formula provides a reliable estimate of how much hull sits below the waterline. It accounts for hull shape through a correction factor: powerboats use 0.85 for their moderate deadrise, while fin-keel sailboats use 0.75 because their narrow underbody offsets the deep keel area.

Always buy slightly more paint than calculated. Rough or pitted hulls absorb more paint, and the waterline band benefits from an extra stripe coat. For the best protection, apply paint in alternating colors (e.g., red first coat, blue second) so you can see when the outer coat wears through.

Related Calculators

Boat Fuel Calculator

Fuel consumption & range

Hull Speed Calculator

Theoretical max speed

Boat Displacement Calculator

Displacement & buoyancy

Sail Area Calculator

Sail sizing & ratios

Boat Winterization Calculator

Calculate antifreeze volumes for engine, water systems, and tanks for boat winterization. Estimate shrink wrap material and total winter storage costs.

Marine Engine Hours Calculator

Estimate your marine engine's remaining life from current hours and usage patterns. Calculate true cost per hour including fuel, maintenance, and depreciation.

Related Resources

How Much Paint Do I Need for a Room? Complete Calculator Guide

Read our guide

DIY vs. Professional Painting Cost in 2026 (Full Comparison)

Read our guide

How Much Does Interior Painting Cost in 2026? (Per Room & Per Sq Ft)

Read our guide

Boat Fuel Calculator

Estimate fuel consumption and cruising range

Hull Speed Calculator

Find maximum hull speed from waterline length

Boat Displacement Calculator

Calculate displacement and buoyancy

More Marine Calculators

Explore all marine and boating tools

View All

Last Updated: Mar 25, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

UseCalcPro
FinanceHealthMath

© 2026 UseCalcPro