Wood Finish Coverage and Coats Calculator

Working out coverage before you start saves you from the worst outcome in finishing: running out mid-coat, then hunting for a matching tin while a half-finished surface dries at two different rates.

Volume needed = (surface area × number of coats) ÷ coverage rate

Coverage is quoted per GALLON, and that is what catches people out. Read a “400 sq ft” figure off a quart tin and you will buy a quarter of what the job needs. Every number in the first column below is square feet per US gallon.

Hard wax oil is the outlier and it is not a misprint. Osmo and Rubio genuinely cover two to three times what polyurethane does, because you are wiping on a film measured in microns rather than building one you can feel with a fingernail. It also means a heavy coat stays tacky for days, so resist the urge.

Stain is not on this list on purpose. Stain is colour rather than protection, it goes on as one coat that is wiped back off, and its coverage swings far more with the wood species than any topcoat does. The stain quantity calculator handles it by species. Whatever it tells you, you still need a topcoat over the top, and that is what this page is for.

Worked example, a dining table. A 4 ft × 6 ft top is 24 sq ft, and the apron adds about 6, so call it 30 sq ft in oil-based polyurethane at 3 coats:

• 30 × 3 = 90 sq ft of coverage needed
• 90 ÷ 400 = 0.225 gallons, which is 0.90 quarts
• A quart tin does it with almost nothing to spare, so buy two if you want a margin
• 2 recoat gaps × 24 hours, plus a 7-day cure, is 9 days before it takes a hot plate

Second example, kitchen cabinet doors. 80 sq ft of doors in waterborne poly at 4 coats: 320 sq ft of coverage, ÷ 365 = 0.88 gallons, so 3.5 quarts. Buy the gallon. It is cheaper than four quarts and you will use it.

What reduces coverage

• Grain porosity. Open-grained woods (oak, ash, mahogany) drink more than closed-grain woods (maple, cherry, birch). The calculator adds 25% when you tell it the grain is open.
• End grain takes three to five times what a face takes. Seal it first or budget separately.
• Rough-sawn stock absorbs far more than planed and sanded stock.
• Cold finish is thicker and covers less. Thin it 5 to 10% below about 15°C.
• Spraying loses a third or more to overspray. Budget half again on top of everything else.

Sanding between coats, the step people skip

Polyurethane takes 220 grit between coats, lacquer and shellac 320, and hard wax oil is buffed rather than sanded. You are breaking the surface for adhesion and knocking off dust nibs, not stripping anything, so a light pass is enough. Never sand the last coat. The marks show, and there is no coat going over the top to hide them.

The recoat window cuts both ways: too soon and the new coat lifts or wrinkles the one under it, too late and it will not key properly without sanding first. Lacquer is the exception, because each coat re-dissolves the one below and the bond is chemical.

Buy the whole quantity in one go, and from one batch. Tinted products and even clear oils shift shade slightly between batches, and a lap of the new tin against the old shows up under a lamp forever.