A 12×20 ft deck (240 sq ft) needs about 2.4 gallons of stain for two coats at 200 sq ft per gallon — buy 3 gallons. With railing on three sides (48 ft), plan on 6 gallons.
Change the numbers
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Your results
Stain to buy3 gallons
Exact amount (2 coats)2.4 gal
Deck surface240 sq ft
Railing (both sides, approx.)0 sq ft
Gallons by coverage rate (2 coats)
Coverage
Floor only (exact)
Floor only (buy)
Floor + railing (buy)
150 sq ft/gal
3.2
4
8
200 sq ft/gal
2.4
3
6
250 sq ft/gal
1.92
2
5
300 sq ft/gal
1.6
2
4
Use the 150 sq ft row for rough, weathered or never-sealed wood and the 250–300 rows for smooth, previously sealed boards.
The math
12 × 20 = 240 sq ft × 2 coats ÷ 200 = 2.4 gal
Common questions
How many gallons of stain for a 12x20 deck?
About 2.4 gallons for two coats on the deck floor (buy 3), or 6 gallons including 48 ft of railing.
