Quick answer
Stain needed (gallons) = length × width × coats ÷ coverage per gallon. A 16 × 12 ft deck (192 ft²) with two coats at 200 ft² per gallon needs 1.92 gallons.
Enter the deck length and width, the number of coats and the coverage on the can. The calculator returns gallons and deck area.
Related tools: Deck Boards Calculator: Number of deck boards for a deck surface. Fence Stain Calculator: Gallons of stain for both sides of a fence.
How to use the Deck Stain Calculator
- Enter deck length (ft) (above 0).
- Enter deck width (ft) (above 0).
- Enter coats (a whole number, between 1 and 5). It starts at 2.
- Enter coverage per gallon (ft²) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Deck length | A number, in ft | > 0 |
| Deck width | A number, in ft | > 0 |
| Coats | A whole number | ≥ 1, ≤ 5, starts at 2 |
| Coverage per gallon | A number, in ft². Printed on the can | > 0 |
Formula and method
Formula
gallons = length × width × coats ÷ coverage
IEEE-754 double precision; shown to the decimals indicated.
Railings and stairs are not included. Plan geometry only; confirm quantities with your supplier and local code before ordering.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Deck length = 16; Deck width = 12; Coats = 2; Coverage per gallon = 200.
| Result | Value |
|---|---|
| Stain needed | 1.92 gal |
| Deck area | 192 ft² |
Example 2
Inputs: Deck length = 20; Deck width = 14; Coats = 1; Coverage per gallon = 250.
| Result | Value |
|---|---|
| Stain needed | 1.12 gal |
| Deck area | 280 ft² |
The first line is the headline result (stain needed). Below it the deck Stain Calculator lists deck area, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Coverage depends on the wood
Coverage on the label is for smooth, sealed wood. Weathered or rough boards can soak up twice as much, cutting coverage to 100 to 150 ft² per gallon. Semi-transparent stains often need only one coat.
Leave out railings and stairs
Railings, balusters and stairs are extra: add their surface area separately. Order a little more than calculated, since matching a batch later can be hard.
How the result changes with deck length
Holding every other input at the first worked example, this table changes only deck length. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Deck length | Stain needed | Deck area |
|---|---|---|
| 8 | 0.96 gal | 96 ft² |
| 16 | 1.92 gal | 192 ft² |
| 32 | 3.84 gal | 384 ft² |
| 64 | 7.68 gal | 768 ft² |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Deck length: entering "0" shows "Deck length must be greater than 0." beside that field and no result.
- Coverage per gallon: entering "0" shows "Coverage per gallon must be greater than 0." beside that field and no result.
Choosing between the Deck Stain Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Deck Boards Calculator](/construction/deck-boards-calculator/) | deck length, deck width and board width | Boards needed |
| [Baluster Calculator](/construction/baluster-calculator/) | railing length, baluster width and maximum gap | Balusters needed |
| [Fence Stain Calculator](/construction/fence-stain-calculator/) | fence length, fence height and coats | Stain needed |
| [Roof Pitch Calculator](/construction/roof-pitch-calculator/) | i know the and value | Pitch |
| [Tile Calculator](/construction/tile-calculator/) | area to tile, tile length and tile width | Tiles needed |
Background: construction estimates
Material quantities are geometry plus a margin. Calculate the exact volume or area, add an allowance for waste, spillage, cuts and uneven ground (calculator pages commonly mention 5 to 10 percent, a rule of thumb that varies by material and job) and round up to whole units. One cubic yard is exactly 27 cubic feet.
Suppliers often have minimum order sizes and may charge for small loads, so confirm quantities, product yields and local code with your supplier or a qualified estimator before ordering.
Assumptions and limitations
- Add railings and stairs separately
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for deck length and coverage per gallon to confirm this.
Frequently asked questions
How long should stain dry?
Typically 24 to 48 hours before foot traffic, per the label.
Do I need two coats?
Many products specify one; check the label.
Should I sand first?
Cleaning and light sanding help the stain absorb evenly.
What does the Deck Stain Calculator calculate?
Gallons of stain for a deck surface. It returns Stain needed and Deck area.
What formula does the Deck Stain Calculator use?
gallons = length × width × coats ÷ coverage. Railings and stairs are not included.
What do I need to enter in the deck Stain Calculator?
You enter Deck length (ft), Deck width (ft), Coats and Coverage per gallon (ft²).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Add railings and stairs separately.
What is an example of a deck Stain result?
With deck length 16, deck width 12, coats 2 and coverage per gallon 200, the stain needed is 1.92 gal.
Can I rely on this calculator for a decision?
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work. For this calculator in particular: Add railings and stairs separately.
Related calculators
- Deck Boards Calculator — Number of deck boards for a deck surface.
- Fence Stain Calculator — Gallons of stain for both sides of a fence.
- Roof Pitch Calculator — Roof pitch as rise per 12 inches, angle, slope percent and rafter length factor.
- Tile Calculator — Number of tiles (and boxes) for an area.
- Aquarium Volume Calculator — Capacity and filled weight of a rectangular aquarium.
Sources
- OpenStax, Prealgebra 2e (Rice University): perimeter, area, volume, circumference and the Pythagorean theorem
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI), Appendix B conversion factors (international foot 0.3048 m, inch 25.4 mm, US gallon 3.785411784 L)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.