Deck stain calculator
How much stain for the deck floor, the railings and the stairs, for one or two coats, and which cans to buy. Spread rates change a lot with the wood, so the answer is a range.
Stain to buy
359 ft² to stain, 1 coat, new, smooth boards (250 ft²/gal to 400 ft²/gal).
- Area to stain359 ft²1 coat = 359 ft² of coating
- Stain needed0.9–1.44 gallikely about 1.11 gal
- Cans to buy1 × 1 gallon + 1 × 1 quartholds 1.25 gal
Spread rate used: 250 ft²/gal to 400 ft²/gal for new, smooth boards. The can's own figure always wins.
| Part | Area | Stain for all coats |
|---|---|---|
| Deck floor | 192 ft² | 0.59 gal (2.2 L) |
| Railings (all faces) | 151 ft² | 0.47 gal (1.8 L) |
| Stairs | 16.1 ft² | 0.05 gal (0.2 L) |
| Other | 0 ft² | – |
| Total | 359 ft² | 1.11 gal (4.2 L) |
| Stain spreads at | Stain needed | Cans |
|---|---|---|
| 400 ft²/gal (best case) | 0.9 gal (3.4 L) | 1 × 1 gallon |
| 325 ft²/gal (middle) | 1.11 gal (4.2 L) | 1 × 1 gallon + 1 × 1 quart |
| 250 ft²/gal (thirsty wood) | 1.44 gal (5.4 L) | 1 × 1 gallon + 2 × 1 quart |
Buy for the middle figure, stain one measured section first, then work out your real spread rate below before buying the rest.
How to use the stain calculator
Tick the parts you are staining and enter their sizes. The floor is length × width. Railings are measured along the top rail and from the deck to the top of the rail; the style sets how much wood that face holds once every baluster, rail and post is counted on all sides. Stairs count each tread, plus the risers if they are boarded in, with 10% added for stringers and board edges.
The surface condition sets the spread rate. Smooth, planed boards soak up less than rough-sawn or grey, weathered wood, so the same can covers much more. If your can gives a figure, choose "Use the spread rate on my can" and type it in: the label always beats a typical range.
Buying
The calculator gives the stain needed at both ends of the range and picks the mix of cans that covers each with the least left over. Buy for the middle figure, stain one measured section, then enter what it really took under "Measured your own spread rate?" before buying the rest.
Worked example
A 16 × 12 ft deck is 192 ft². 28 ft of baluster railing 36 in high is 28 × 3 × 1.8 = 151 ft², and four 48 × 11 in treads add about 16 ft². That is 359 ft² in all. At 250 to 400 ft² per gallon, one coat takes 0.9 to 1.44 gallons, about 1.1 at the middle rate of 325: a 1 gallon can and a quart.
Spread rates printed by stain makers
These are the figures on the data sheets we checked. They show how wide the spread is, and why the can in your hand matters more than any average.
| Product | Smooth wood | Rough wood | Coats |
|---|---|---|---|
| ZAR Deck & Siding Semi-Transparent | 300–400 ft² (7.4–9.8 m²/L) | 100–200 ft² (2.5–4.9 m²/L) | one |
| Olympic MAXIMUM Semi-Transparent | 250–350 ft² (6.1–8.6 m²/L), "depending upon wood texture" | one thin coat | |
| Olympic MAXIMUM Solid Color | 350–500 ft² (8.6–12.3 m²/L) | two | |
| BEHR PREMIUM Solid Color (No. 5011) | 200–400 ft² (4.9–9.8 m²/L), by application method and porosity | see label | |
The calculator's ranges come from these: 250–400 ft² per gallon for smooth boards and 100–200 for rough-sawn. No label we found gives a separate figure for weathered wood, only that porous wood covers less, so the weathered range of 150–250 ft² per gallon is our own assumption between the two. Railing multipliers (1.8 for balusters, 2.3 for solid boards, 0.8 for posts and rails only) are our estimates from common part sizes, not a published figure.
Sources
- ZAR (Sika), ZAR Deck and Siding Semi-Transparent product data sheet: coverage on smooth and rough surfaces, one-coat application.
- PPG, Olympic MAXIMUM Semi-Transparent technical data sheet 79560 and Olympic MAXIMUM Solid Color technical data sheet 79611: coverage and number of coats.
- Behr, BEHR PREMIUM Solid Color Waterproofing Stain & Sealer No. 5011 technical data sheet: coverage by application method and porosity.
Questions
How much stain do I need for a 12 × 12 ft deck?
The floor alone is 144 ft². At 250 to 400 ft² per gallon on smooth boards, one coat takes about 0.4 to 0.6 gallons (1.4 to 2.2 L). Rough or weathered boards can take twice that, and railings and stairs often add as much again as the floor.
Should I put on one coat or two?
Follow the can. The semi-transparent stains we checked are one-coat products, and ZAR's sheet warns that more is not better because the stain has to soak in. Olympic's solid colour stain asks for two coats. Choose 2 coats here only if your label does.
Why is the range so wide?
Wood drinks stain at very different rates. ZAR's data sheet gives 300 to 400 ft² per gallon on smooth surfaces but only 100 to 200 on rough ones. Age, species, how dry the boards are and whether you brush or spray all move the figure, which is why a measured test section is worth doing.
How do I work out my own spread rate?
Measure a section, say ten boards across the deck, and note the stain level before and after. Divide the area by the stain used: 70 ft² from a third of a gallon is 210 ft² per gallon. Enter both numbers in the helper and press "Use this spread rate".