Wood Stain Calculator
Gallons for a deck, fence or any wood surface — with a second coat that costs less than the first.
Stain to buy
2 × Gallon
- Surface area
- 320 sq ft
- Area equivalent, 2 coats
- 528 sq ft (×1.65)
- Stain needed
- 1.76 gal
- With 5% waste
- 1.85 gal
- Purchased
- 2.00 gal
- Leftover
- 0.15 gal
Buy the whole quantity in one batch. Colour varies between production batches, and the join shows on a fence for years.
Building the deck first? Use the deck board calculator →
How this is calculated
area = deck L × W, or fence L × H × sides, plus railing ft × sq ft/ft coat factor = 1 + (coats − 1) × recoat% gallons = area × coat factor / coverage buy = gallons × (1 + waste%) containers = ceil( buy / container size )
The coat factor is the part most calculators get wrong. Bare wood soaks up the first coat; the second lands on a partly sealed surface and uses roughly two thirds as much. Two coats therefore cost about 1.65 times one coat, not twice. Over a large fence that difference is a full pail.
Coverage is the other lever, and it moves further than anything else here. The figure on the can is measured on smooth new lumber. Weathered decking and rough-sawn fence boards have far more surface than their footprint suggests and can take less than half the label rate, which is why the surface condition selector changes the answer more than the number of coats does.
Coverage by wood condition
| Condition | First coat | Gallons per 500 sq ft | Two coats at 65% |
|---|---|---|---|
| Smooth planed, new | 400 sq ft/gal | 1.25 | 2.06 |
| Smooth, previously finished | 450 sq ft/gal | 1.11 | 1.83 |
| Pressure-treated, new | 300 sq ft/gal | 1.67 | 2.75 |
| Cedar or redwood, smooth | 325 sq ft/gal | 1.54 | 2.54 |
| Weathered or greyed | 200 sq ft/gal | 2.50 | 4.13 |
| Rough sawn or textured | 175 sq ft/gal | 2.86 | 4.71 |
| Old deck, dry and thirsty | 150 sq ft/gal | 3.33 | 5.50 |
First-coat rates on bare wood, from manufacturer data sheets. Both gallon columns are computed by the same arithmetic the tool runs. Note that the worst case takes three times the best case for identical square footage — the wood matters more than the product.
Typical projects
| Project | Area | One coat, smooth | One coat, rough | Two coats, rough |
|---|---|---|---|---|
| 10 × 12 ft deck | 120 sq ft | 0.30 gal | 0.69 gal | 1.13 gal |
| 16 × 20 ft deck | 320 sq ft | 0.80 gal | 1.83 gal | 3.02 gal |
| 20 × 24 ft deck | 480 sq ft | 1.20 gal | 2.74 gal | 4.53 gal |
| 50 ft of 6 ft fence, one side | 300 sq ft | 0.75 gal | 1.71 gal | 2.83 gal |
| 100 ft of 6 ft fence, both sides | 1200 sq ft | 3.00 gal | 6.86 gal | 11.31 gal |
| 40 ft of railing with balusters | 180 sq ft | 0.45 gal | 1.03 gal | 1.70 gal |
Deck figures cover the walking surface only. Add the railing separately, and add the stairs, which have a tread, a riser and two exposed edges for every step.
Frequently asked questions
How much stain do I need for a deck?
Divide the deck area by the coverage rate for your surface, then add the railing separately. A 16 by 20 ft deck is 320 square feet, which is about one gallon on smooth new wood and closer to two on weathered boards. Railing is the part people forget: forty feet of rail with balusters adds roughly the same area again as a small deck, because every baluster has four faces.
Does a second coat use as much as the first?
No, and assuming it does is why people end up with a half-full can. Bare wood absorbs most of the first coat; the second one sits largely on a surface that is already partly sealed and typically uses 55 to 70% as much. Semi-transparent stain on a smooth deck can be nearer half. The calculator applies that factor rather than simply multiplying by the number of coats.
How much stain for a fence?
Multiply the fence length by its height, then double it if you are doing both sides, and expect rough-sawn pickets to take about 175 square feet per gallon rather than the 300 to 400 on the label. A 100 ft run of 6 ft privacy fence is 600 square feet per side, so both sides at one coat is roughly seven gallons on rough wood. Buying in five gallon pails is materially cheaper at that quantity, and it also avoids the batch-to-batch colour variation you get across seven separate cans.
Is coverage on the can accurate?
It is accurate for the surface the manufacturer tested on, which is nearly always smooth, new, planed lumber. Real decks and fences are rougher, older and drier than that, so the honest planning figure is often half the label. Treat the label as the best case, buy against the rougher estimate, and keep the receipt for the unopened extra.
Should I buy one large pail or several cans?
One pail, whenever the quantity justifies it. Stain colour varies slightly between production batches, and a fence finished from two batches can show the join in daylight for years. If you must use multiple cans of the same colour, box them: pour them all into a larger container, mix, and work from that. This matters more with semi-transparent and solid stains than with clear sealers.
How much should I add for waste?
About 5% for a brush or roller job, and 20 to 30% if you are spraying, because overspray and what stays in the pump and hose is real material. Spraying a fence outdoors on a breezy day loses more than that. A small excess is cheap insurance: running out mid-deck means a lap mark where the wet edge dried, and that line does not disappear under the next coat.
Results are planning estimates. Coverage varies by product, application method, wood species and how dry the wood is on the day. Follow the manufacturer instructions on surface preparation and recoat timing, and test the colour on an offcut before committing to the whole deck.