Wood Finish Coverage Calculator
Work out how much oil, poly, lacquer or stain you need for a project — from surface area, number of coats and the finish’s spread rate.
How it works
Gallons = (area ft² × coats) ÷ spread rate ft² per gallon · 1 gal = 4 qt = 128 fl oz
Finish coverage is just area divided by the product’s spread rate, multiplied by the number of coats. Spread rate varies a lot by finish: thin, penetrating products like Danish oil and stain cover less because the wood drinks them in, while film finishes like poly and shellac lay on top and stretch further. Bare, porous, or end-grain-heavy wood soaks up noticeably more on the first coat than on later ones, so treat these figures as a planning estimate and buy a bit extra. Remember to count both faces and all edges of your parts when you measure the area — it is easy to forget the undersides.
Worked example
A tabletop and apron total about 100 ft² of surface, and you want two coats of oil-based poly (~450 ft²/gal). Finish = 100 × 2 ÷ 450 = 0.444 gal, which is 1.78 quarts — so a two-quart can just does it, but a gallon leaves room for the inevitable spills and a third coat.
Frequently asked questions
Why does the first coat use more?
Bare wood is porous and absorbs finish, especially on end grain and open-pored species like oak. The first coat seals those pores, so second and third coats spread further. Plan for the first coat to use noticeably more than the average.
How do I measure a complex project’s area?
Break it into rectangles — top, sides, shelves, edges — and add them up, counting every face that gets finished (including undersides and insides). For turned or carved work, estimate generously; it is cheaper to have leftover finish than to run out mid-coat.
Do thinned finishes change the math?
Yes. Thinning a wiping varnish or shellac makes each coat go on thinner, so it covers more area per coat but you generally need more coats to build the same film. The total product used ends up similar; the coverage per coat just rises.
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This calculator is for educational purposes. Double-check important results before acting on them.