Wood Stain Calculator
Buying the right amount of wood stain avoids both a wasted second trip to the store and leftover cans. The amount you need is the surface area divided by the product's coverage rate per gallon, multiplied by the number of coats. Coverage depends heavily on the product and how porous the wood is, so it is a user-editable input you read from the can. This calculator shows the exact gallons needed and the whole gallons to buy after rounding up, plus the area covered per coat.
Wood stain formula
Total area = surface area x number of coats
Stain needed (gallons) = total area / coverage rate
Gallons to buy = round up (stain needed)
Stain needed (quarts) = gallons x 4
The math is a simple ratio of area to coverage, scaled by coats. The coverage rate comes from the product label because it depends on the stain and the wood's porosity, both of which you alone can read for your project.
Staining context
- Rough or unsealed wood absorbs much more stain than smooth, sealed timber.
- Coverage rates are printed on the product label; always use that figure.
- For a fence, double the area if you stain both sides.
- Round up to whole containers to avoid lap marks from running out mid-coat.
- A second coat often uses slightly less than the first as the surface seals.
Wood stain: frequently asked questions
How much wood stain do I need?
Divide the surface area to be stained by the product's coverage rate per gallon, then multiply by the number of coats. For example, 400 square feet at 250 square feet per gallon for two coats needs 400 / 250 x 2 = 3.2 gallons, so you would buy 4 gallons. Always round up to whole containers.
Why is the coverage rate an editable input?
Coverage varies a great deal by product, wood porosity and application method. Rough or unsealed wood soaks up far more stain than smooth, sealed timber. The manufacturer prints a coverage rate on the can, so this calculator asks you to enter that figure rather than guess, which keeps the estimate accurate for your product.
How do I measure the surface area?
For a deck or floor, multiply length by width. For a fence, multiply length by height, and double it if you stain both sides. For furniture, add up the area of each face. Enter the total square footage. Subtract large openings if you wish, but a small margin of extra stain is usually welcome.
Should I always round up?
Yes. Stain is sold in fixed container sizes, and running out partway through a coat risks a visible lap mark where a new batch begins. Buying slightly more also lets you keep a small amount for touch-ups. This calculator shows the exact amount needed and you round up to the next whole container.
Does a second coat use as much as the first?
Often a little less, because the first coat seals the surface and reduces absorption. This calculator multiplies by the number of coats using the same coverage rate, which is a safe planning assumption. If the manufacturer gives a separate second-coat rate, you can lower the coats figure proportionally.
Official sources
- U.S. Forest Products Laboratory: Wood finishing publications.
- U.S. National Institute of Standards and Technology: Office of Weights and Measures (units of volume).
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.