How it works
The calculator multiplies the floor area by the number of coats, divides by the finish’s coverage and rounds up to whole cans.
Floor area = Length × Width
Finish = Floor area × Coats ÷ Coverage × (1 + Extra ÷ 100)
Cans = ⌈ Finish ÷ Can size ⌉
⌈ ⌉ means rounding up to the next whole number: you can’t buy part of a can. The finish volume itself is not rounded. In “known floor area” mode the area you enter replaces length × width.
The worked example
A 15 × 12 ft room has 180 sq ft of floor. Varathane’s data sheet for its Water-Based Floor Polyurethane gives a practical coverage of 400–500 sq ft per gallon and recommends a minimum of 4 coats. At the low end, four coats take 180 × 4 ÷ 400 = 1.8 gallons – two one-gallon cans. With Bona Traffic HD at 350 sq ft per gallon and the two finish coats of Bona’s system, the same room needs 360 ÷ 350 = 1.03 gallons; in quart cans that is 4.1 quarts, so five quarts.
Coverage differs between finishes
Floor finishes differ in how much solid material they lay down per coat. The data sheets used here run from 350 sq ft per gallon (Bona Traffic HD) to 500–600 (Bona Mega ONE). That is why the calculator has no generic “polyurethane coverage” figure: pick your product to apply the rate from its manufacturer’s data sheet, or type the figure from your can. Where a sheet gives a range, the low end is used, so the estimate leans towards more finish. Varathane’s practical coverage figure already assumes 15 % material loss.
Coats
The coat count matters more than anything else in the result, because the finish scales directly with it. Follow the number on your product’s label: Varathane, for example, calls for at least four coats of its water-based floor finish but a total of two of its oil-based one. Bona’s waterborne finishes are applied over a Bona sealer or stain: that first coat is a separate product and is not included here.
Units
Measurements, coverage and can size are converted to one internal unit before calculating, so you can enter the room in feet and inches and pick gallons or quarts. One US gallon is 231 cubic inches (NIST Handbook 44) and equals four quarts. In metric, coverage is in m² per liter; can sizes vary by brand and market, so none is filled in – enter the size you’ll buy to see the number of cans.
Worked example
Inputs
- Measure by
- Room length × width
- Room length
- 15 ft
- Room width
- 12 ft
- Number of coats
- 4
- Floor finish
- Varathane Water-Based Floor Polyurethane – 400 sq ft/gal (≈ 9.8 m²/L)
- Extra finish
- 0 %
- Can size
- 1 gal
Result
- Floor area
- 180 sq ft
- Coverage used
- 400 sq ft/gal
- Finish needed
- 1.8 gal (7.2 qt)
- Cans
- 2
Common mistakes
- Counting the finish coats but forgetting the sealer or stain coat under them. It is usually a different product with its own coverage.
- Spreading the finish thinner to make a can go further. Bona’s sheets say to use the recommended coverage and not to spread too thin.
- Using the coverage of one finish for another. Waterborne, oil-modified and oil-based finishes have different solids and different spread rates.
- Buying exactly the calculated amount in several batches. Buy enough for every coat at once so you don’t run out between coats.
- Leaving out closets, hallways and thresholds that will be finished at the same time.
Assumptions and limits
- The floor is a rectangle of length × width, or the area you enter.
- Coverage is the documented rate of the product you pick – the low end of the range on its data sheet – or the figure you type, and it applies to every coat.
- The number of coats is the number of finish coats. A sealer, stain or primer coat is not included.
- Cans are rounded up to whole cans of the size you choose; the calculator does not mix gallons and quarts.
- Real coverage depends on the wood species, how it was sanded, the applicator and the temperature.
Frequently asked questions
How many square feet does a gallon of polyurethane floor finish cover?
It depends on the product. The data sheets used here list 350–400 sq ft per gallon for Bona Traffic HD, 500–600 for Bona Mega ONE, 400–500 for Varathane Water-Based Floor Polyurethane and 400–500 for Varathane Premium Floor Finish (250 VOC). The calculator uses the low end of each range, per coat.
How many coats of polyurethane does a floor need?
Follow the label of your finish. Varathane recommends a minimum of 4 coats of its Water-Based Floor Polyurethane but a total of 2 coats of its oil-based Premium Floor Finish (250 VOC). Bona’s systems are a Bona sealer or stain plus 2 coats of finish, with a third coat recommended in heavy-traffic areas.
Should I buy gallons or quarts?
Enter both and compare. Set the can size to a gallon, then to a quart, and compare the prices of the two results. The calculator rounds up to whole cans of the size you choose.
Does a recoat of an existing floor need the same amount?
Each coat needs about the same amount, so a one-coat refresh takes the coverage of one coat. Follow the maker’s instructions for preparing a previously finished floor first.
Sources
- Bona Traffic HD Two-Component Waterborne Finish – Technical Data Sheet (05/27/2026) — Bona US. "Coverage: 350-400 square feet per gallon" (preset uses 350); system: a Bona sealer or stain and 2 coats, a third coat in heavy-traffic areas.
- Bona Mega ONE – Spec Sell Sheet (item 4681) — Bona US. "Coverage: 500-600 square feet per gallon" (preset uses 500); "Apply a Bona sealer or Bona stain and 2 coats of Bona Mega ONE", a third coat in heavy-traffic areas.
- Varathane Water-Based Floor Polyurethane – Technical Data VAR-05 (Form GDH-433) — Rust-Oleum Corporation. "Practical Coverage at Recommended DFT (assumes 15% material loss) 400-500 sq.ft./gal." (preset uses 400); "A minimum of 4 coats is recommended."
- Varathane Premium Floor Finish (250 VOC) – Technical Data VAR-51 (Form GDH-862) — Rust-Oleum Corporation. "COVERAGE: 400-500 square feet/gallon" (preset uses 400); "A total of 2 coats are recommended."
- NIST Handbook 44, Appendix C – General Tables of Units of Measurement — National Institute of Standards and Technology. Exact unit definitions: 1 in = 2.54 cm, 1 yd³ = 27 ft³, 1 US gal = 231 in³, 1 lb = 0.45359237 kg.
Method reviewed November 5, 2026