About this calculator
Most deck stain estimates count only the floor, and that’s why people run out halfway. Stairs add a tread and a riser for every step, and a railing has two faces: the railing on a typical deck takes about as much stain as the floor itself. This deck stain calculator adds up all three, multiplies by the coats, divides by the coverage on your can, and tells you how many gallons to buy.
It also checks whether a 5 gallon pail is cheaper than single gallons at your prices, gives the range you can expect on smooth or rough wood, and works out the deck cleaner to prep with. The drawing shows the deck, its stairs and railing, and a bar of the stain each part takes, laid over the cans you’ll buy so you can see what’s left over.
How to use it
- Measure the deck’s length along the house and its width out from the house.
- Count the stair steps and measure their width. Choose whether you’re staining a railing on the three open sides, and enter its height.
- Enter the coats and the coverage per gallon from your stain’s label. Use the low end for old, rough or weathered wood.
- Open Your local prices to compare single gallons with a 5 gallon pail and see the cost.
The formula
Deck = length × width
Stairs = steps × stair width × (11³⁄₁₆ in tread + 7½ in riser)
Railing = (2 × width + length − stair width) × height × 2 faces
Stain = (deck + stairs + railing) × coats ÷ coverage per gallon
Buy = whole gallons, as 5 gallon pails where that’s cheaper
Cleaner = area ÷ 750 sq ft per gallon of concentrate
A 16 × 12 ft deck is 192 sq ft. Three 4 ft steps add 3 × 4 × 18.69 ÷ 12 = 18.7 sq ft, and a 36 in railing on the three open sides (12 + 12 + 16 − 4 = 36 ft) adds 36 × 3 × 2 = 216 sq ft, for 426.7 sq ft in all. One coat at 250 sq ft per gallon takes 1.71 gallons, so buy 2. Counting each baluster and rail of a 36 in railing gives about the same area as the two faces of a solid panel.
Worked example
These are the calculator’s starting values and the results they produce:
| Deck length (along the house) | 16 ft |
|---|---|
| Deck width (out from the house) | 12 ft |
| Stair steps (treads) | 3 |
| Stair width | 4 ft |
| Railing | Railing on the three open sides |
| Railing height | 36 in |
| Coats of stain | 1 |
| Stain coverage per gallon | 250 sq ft |
| Deck stain, per gallon | $45.00 |
| Deck stain, 5 gallon pail | $170.00 |
| Deck cleaner concentrate, per gallon | $25.00 |
Tips before you buy
- Clean before you stain. Spray on a deck cleaner or brightener, scrub, rinse and let the wood dry; stain on dirty or gray wood won’t soak in and peels early.
- New pressure-treated wood often needs to dry for weeks first. Sprinkle some water on it: if it soaks in within a few minutes, it’s ready for stain.
- Stain on a dry, mild day with no rain due for 24 hours, out of strong sun. Do the railing first, then the floor a few boards at a time along their full length so laps don’t show.
- Buy all the stain at once and mix the cans together (box them) so the color is even across the deck.
- Two coats of a penetrating stain don’t always mean twice the stain: the second soaks in less. Many labels call for one coat, or a second one wet-on-wet; follow yours.
Frequently asked questions
How much stain do I need for a 12 × 16 deck?
The floor alone is 192 sq ft, or 0.77 gallons for one coat at 250 sq ft per gallon: one gallon. With three 4 ft steps and a 36 in railing on the three open sides, the area is about 427 sq ft and one coat takes 1.71 gallons: buy 2.
How many square feet does a gallon of deck stain cover?
It depends on the stain and the wood. SuperDeck’s semi-transparent stain lists 250–350 sq ft per gallon on smooth wood and 150–250 on rough-sawn wood; ZAR’s lists 300–400 smooth and 100–200 rough; Cabot’s 200–650. Old, weathered wood soaks up more, so use the low end of the label.
How much stain does a deck railing take?
Count both faces of the railing as if it were solid: length × height × 2. A 36 ft run of 36 in railing is 216 sq ft, or 0.86 gallons for one coat at 250 sq ft per gallon: about half the stain for a 12 × 16 ft deck with stairs.
Is a 5 gallon pail of deck stain cheaper?
Usually from 4 gallons up. At $45 a gallon and $170 a pail, two coats on a 12 × 16 ft deck with three steps and a railing take 3.41 gallons; four single gallons cost $180, so one 5 gallon pail at $170 is cheaper and leaves about 1.6 gallons for touch-ups.
Sources
Areas and volumes are standard geometry. The published figures this calculator relies on come from these sources; other defaults (waste allowances, typical densities and prices) are common trade figures worth checking with your supplier.
- Duckback SuperDeck Semi-Transparent Stain data sheet (SC 2100–2300): 250–350 sq ft per gallon on smooth wood and 150–250 on rough-sawn wood, one coat
- ZAR Deck & Siding Semi-Transparent Stain product data sheet (Sika): 300–400 sq ft per gallon on smooth surfaces and 100–200 on rough surfaces
- Cabot Semi-Transparent Stain + Sealer: 200–650 sq ft per gallon
- Wolman Deck & Fence Brightener data sheet: 1 gallon of brightener concentrate covers about 750 sq ft
- International Residential Code 2021, Chapter 3 (R311.7, stairways): stair risers up to 7¾ in