What Is the Deck Stain Calculator?
This tool estimates how many gallons of stain you need to cover a deck. It multiplies the deck's surface area by the number of coats, then divides by the coverage rating of your stain (typically 200–300 sq ft per gallon). The result tells you both the exact amount and how many full gallons to buy.
How to Use It
Enter your deck's length and width in feet, the number of coats you plan to apply, and the coverage rate printed on the stain can (often 250 sq ft/gal for semi-transparent products). The calculator returns your deck area, total area to be stained, exact gallons required, and gallons rounded up so you don't run short mid-project.
The Formula Explained
First, deck area = length × width. Then total area = area × number of coats, because each coat re-covers the whole surface. Finally, gallons = total area ÷ coverage per gallon. Because stain is sold in whole gallons, we round up with the ceiling function so you always have enough.
$$\text{Gallons} = \left\lceil \frac{\text{Length (ft)} \times \text{Width (ft)} \times \text{Coats}}{\text{Coverage (sq ft/gal)}} \right\rceil$$
Worked Example
For a 16 ft × 12 ft deck with 2 coats and 250 sq ft/gal coverage: area = 192 sq ft, total area = 384 sq ft, gallons = 384 ÷ 250 = 1.536 gal. Rounded up, you'd buy 2 gallons.
$$\text{Gallons} = \left\lceil \frac{16 \times 12 \times 2}{250} \right\rceil = \left\lceil \frac{384}{250} \right\rceil = \lceil 1.536 \rceil = 2$$
FAQ
How many coats should I apply? Most deck stains recommend 1–2 coats. Bare or weathered wood often needs two.
What coverage should I use? Check the product label. Smooth wood absorbs less (300 sq ft/gal); rough or porous wood absorbs more (150–200 sq ft/gal).
Should I include railings and stairs? This tool calculates the deck floor only. Add roughly 20% extra for railings, balusters, and stairs.
