It's easy to calculate approximately how much antifouling paint you will need in order to paint your boat. Start by multiplying the length of your boat's hull (LOA) by its beam (B), and multiply again by 0.85. This formula, (LOA x B x 0.85), estimates the surface area to be painted in sq feet. Then, check the coverage of the paint you've chosen. Below is a table showing typical amounts of bottom paint needed for various boat sizes. Keep in mind that actual square footage and coverage varies by boat and paint.
| Boat Type | Amount of Paint |
| 10' Dinghy | 1 Quart |
| 14' Outboard | 1-2 Quarts |
| 18' Runabout | 2 Quarts |
| 20' Sailboat | 3 Quarts |
| 24' Runabout | 3-4 Quarts |
| 30' Sailboat | 1.5 Gallons |
| 32' Cruiser | 1.5-2 Gallons |
| 36' Auxiliary | 2 Gallons |
| 40' Sailboat | 2.5 Gallons |
| 45' Sailboat | 3-3.5 Gallons |
| 50' Sportfisher | 4 Gallons |
Remember, most antifouling paints feature ablative or self-polishing formulas, and wear away as the boat moves through the water, so you will want to apply 2 coats*. Applying only a single coat to your boat's bottom may result in ineffective protection from barnacles, slime, and weeds.
Important: Apply an extra coat to leading and trailing edges, the waterline, rudder, outdrives, trim tabs, and keel.
*The exception to this are hard modified epoxy paints, where a single coat (assuming complete coverage) can be used.