Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Calculate paint or stain gallons needed for any surface area using a specific product's coverage rate.
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Not every painting project is a room's walls -- fences, decks, cabinets, and trim all have their own surface areas and often use products (stains, sealants, specialty paints) with very different coverage rates than standard wall paint. This calculator works from any surface area and any product's stated coverage rate, without assuming a room or subtracting openings.
Enter your surface area, your specific product's coverage rate in sqft per gallon (check the product label -- stains and specialty coatings often cover significantly less than standard wall paint), and your number of coats.
Gallons = (Surface Area × Coats) ÷ Coverage per Gallon
Unlike the room-specific Paint Calculator, this tool doesn't subtract door/window openings -- if you're painting an actual room's walls, use that calculator instead for the more accurate net-area math.
Use this for fences, decks, cabinets, trim, exterior siding, or any project where the coverage rate differs meaningfully from standard interior wall paint.
The number you enter for coverage drives the answer, so use the one on your product's label and adjust for your surface. Labels typically give coverage for smooth, sealed surfaces. Rough-sawn wood, weathered decks, and unfinished lumber absorb more product, so the effective coverage is lower than the label. If the label lists a range, such as one number for smooth surfaces and a lower one for rough, use the lower end for rough or porous wood. Some products also list a different coverage for the first coat and second coat.
Suppose a deck floor is 12 by 16 feet, or 192 square feet, plus a railing you estimate at 60 square feet of surface, for 252 total. You plan two coats of a stain rated at 200 square feet per gallon on rough wood (hypothetical values). Gallons are 252 times 2, divided by 200, or 2.52. Rounding up gives 3 gallons. If the first coat soaks in and the second goes on more thinly, the real usage might be different, so check the product's instructions for recoat timing and expected coverage.
The gallons figure is the amount of product needed to reach the coats you entered at the coverage rate you entered. It is an estimate rather than a guarantee, so consider buying slightly more, particularly for stain, where matching batches later may be difficult. Some products should be mixed together from several cans (boxed) for consistent color, so buy all the cans you need at the same time.
The calculator uses a single coverage rate across the whole surface. If part of your project is rough and part is smooth, calculate them separately. It also ignores waste from spills, roller loss, and cleanup, which can be meaningful with sprayers.
Stains, especially on porous or rough-sawn wood, absorb more deeply into the surface than paint's film-forming coating, so a gallon typically covers less area.
Use the Paint Calculator for room walls/ceilings, since it correctly subtracts door and window openings from the total area.
Multiply length by height for one side, then double it if both faces will be coated. Enter the total as the surface area.
For rough, porous, or weathered surfaces, use the lower number. For smooth, sealed, or previously coated surfaces, the higher number is more realistic.
Yes. Enter the primer's coverage rate and a single coat unless the label calls for more.
It often does, because some product is lost to overspray and the layer can be applied more thickly. Consider a lower coverage rate if you spray.