Understanding your result
The headline is the finish for all coats, and the sub-line gives the cans and the sealer. The three figures show the floor area, the finish per coat and the cans.
The table shows the area, the finish with its coverage, the quantity per coat, the total with the allowance and cans, and the sealer coat. The per-coat figure is useful on the day: it is the amount to pour into the tray for each pass, so you know when a coat is spread too thin.
Floor finish is the last stage of a sanded floor. The wood stain calculator gives the stain if the floor is being coloured first; the drying and recoat calculator stretches the data-sheet recoat times for your temperature and humidity; and the concrete floor calculator covers slabs instead of boards.
How we calculate this
The coverages are the figures on floor-finish data sheets for sanded wood: about 500 sq ft per gallon per coat for oil-modified polyurethane, 450 for water-based and 300 for hardwax oil, whose first coat soaks in. The default coats are the usual schedules: 3, 4 and 2. The 10% allowance covers the applicator, the pad and the tray. The coverage rates table lists floor finishes with the other coatings, and the drying times table gives their recoat windows.
The drying and cure guide explains the difference between dry, recoatable and cured, which matters more on a floor than anywhere else.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Oil-based polyurethane | 500 sq ft per gallon, 3 coats | Floor-finish data sheets (Minwax, Varathane, Bona): 500–600 |
| Water-based polyurethane | 450 sq ft per gallon, 4 coats | Water-based floor-finish data sheets (Bona, Minwax): 450–550 |
| Hardwax oil | 300 sq ft per gallon, 2 coats | Hardwax-oil data sheets (Osmo, Rubio Monocoat and similar): 300–400 on the first coat |
| Sealer | 450 sq ft per gallon | Floor sealer data sheets |
| Allowance | 10% | Applicator and pad loss |
Assumptions last reviewed October 8, 2026.
The calculator does not model sanding, stain, wood filler, or the much lower coverage of the first coat on very open-grained or soft wood. Single-coat oil systems are hardwax with one coat. It does not cover stair treads separately; add their area.
Two worked examples
A bedroom floor in oil-based polyurethane
18 × 14 ft, sanded, sealer coat, three coats.
- Area: 252 sq ft; per coat: 252 ÷ 500 = 0.5 gallons
- Finish: 0.504 × 3 × 1.10 = 1.66 gallons, buy a gallon and three quarts
- Sealer: 252 ÷ 450 × 1.10 = 2.46 quarts, buy three quarts
The same floor in water-based polyurethane at four coats is 2.46 gallons; in hardwax oil at two coats, 1.85 gallons and no sealer.
The metric version
5.5 × 4.3 m, oil-based polyurethane, three coats with a sealer.
- Area: 23.7 m²; per coat: 1.93 litres
- Finish: 6.36 litres, a 5 L and a 2.5 L can
- Sealer: 2.36 litres, a 2.5 L can
Where to find your inputs
Floor size. Length and width of the room, plus closets and hallways being finished with it.
Finish. On the can; the label gives the coverage and the number of coats.
Sealer. Tick it on bare, freshly sanded wood when the product system includes one.
Common mistakes
- One thick coat. Floor finishes are built in thin coats; thick ones wrinkle or stay soft.
- Skipping the screen between coats. Dust nibs and poor adhesion.
- Mixing systems. Use the sealer the finish maker specifies.
- Water-based over oil stain too soon. Wait for the stain to dry fully.
- Rugs in the first week. They trap solvent and mark the finish.
- Forgetting the closets. They are floor too.
Questions people ask
- How much polyurethane for a floor?
- An 18 × 14 ft room is 252 sq ft. Oil-based polyurethane covers about 500 sq ft per gallon per coat, so each coat is about half a gallon and three coats with a 10% allowance are 1.66 gallons, a gallon and three quarts, plus about three quarts of sealer on bare wood.
- How many coats of finish does a wood floor need?
- Three coats of oil-based polyurethane, or four of water-based, which goes on thinner, is the usual schedule on sanded wood. Hardwax oils take two. A maintenance recoat on a sound floor is one coat after screening.
- Oil-based or water-based?
- Oil-based builds faster, ambers with age and needs about a day between coats. Water-based stays clearer, dries in hours so several coats fit in a day, and has less odour, but needs one more coat for the same film.
- What is a sealer coat?
- A first coat that seals the bare wood and, with some products, reduces tannin bleed and grain raising. Some systems use the finish itself as the first coat; others specify a separate sealer. Hardwax oils do not use one.
- Do I need to sand between coats?
- Lightly, yes, with a buffer and screen or 220 grit, then vacuum and tack. It flattens dust nibs and gives the next coat something to grip. Many water-based systems allow two coats without sanding if the second goes on within the recoat window.
- How long before I can use the floor?
- Socks after about a day, furniture after about three to seven days, and rugs after one to two weeks, depending on the finish. The full cure, when the film reaches its hardness, takes up to a month for oil-based polyurethane.