Enter the length and width of the deck, add any stairs or railings as extra area, and choose smooth or rough wood. The calculator multiplies the area by the number of coats, divides by the coverage of the stain and rounds to gallons and quarts.
How the deck stain calculator works
- Area = length × width of the deck floor, plus the extra area you enter for stairs, railings or benches.
- Stain = area × coats ÷ coverage, plus the extra percentage.
- Coverage is 300 sq ft per gallon on smooth, new or sanded boards and 150 sq ft per gallon on rough, weathered or old wood, which soaks up much more stain.
The rates come from the data sheet for ZAR Deck & Siding Semi-Transparent Stain, which lists 300 to 400 sq ft per gallon on smooth surfaces and 100 to 200 on rough surfaces. Solid and semi-transparent stains from other makers cover differently, so check the can.
Stain for common deck sizes
| Deck | Floor area | Smooth wood (300 sq ft/gal) | Rough wood (150 sq ft/gal) |
|---|---|---|---|
| 10 × 10 ft | 100 sq ft | 0.37 gal | 0.73 gal |
| 12 × 12 ft | 144 sq ft | 0.53 gal | 1.06 gal |
| 16 × 12 ft | 192 sq ft | 0.70 gal | 1.41 gal |
| 16 × 16 ft | 256 sq ft | 0.94 gal | 1.88 gal |
| 20 × 16 ft | 320 sq ft | 1.17 gal | 2.35 gal |
Worked example
A 16 × 12 ft deck has 192 sq ft of floor. Its stairs and railings add about 60 sq ft, for 252 sq ft in total. The boards are a few years old and weathered, so the coverage is 150 sq ft per gallon. One coat with 10% extra needs 252 ÷ 150 × 1.1 = 1.85 gallons: two gallons. On new, smooth boards it would be 0.92 gallons, so one gallon.
Measuring stairs and railings
- Stairs: for each step, add the tread (width × depth) and the riser (width × height), plus the two stringers.
- Railings: a quick estimate is the railing length × its height × 2 for both sides of open balusters. Solid panels count once per side.
- Do not count the underside of the deck unless you plan to stain it.
Step by step: estimating and staining a deck
Tips before you buy
- Buy all the stain from the same batch, or mix the cans together, so the color matches.
- Test the color on a hidden board; the same stain looks darker on old, porous wood.
- The deck board calculator counts boards and screw boxes for a new deck.
- See the deck board spacing guide if you are building or replacing boards.
