Paint Calculator
Gallons for a room: wall area is the perimeter times the ceiling height; set coats to 2 for a colour change and add the ceiling if you are painting it. Coverage is 350 ft² per gallon on smooth, primed drywall — textured or bare walls drink more. Doors and windows are not subtracted; they cover the trim paint.
Order 3 gallons (1 five-gallon pails) — one gallon covers 350–400 ft² per coat; buy a 5-gallon pail above 4 gallons — it is cheaper and one batch.
- Wall area
- 768 ft²
- Waste / cuts 5%
- + 38 ft²
- Coverage to buy
- 806 ft²
- Metric
- 71.3 m²
- Gallons (350 ft² each)
- 3
- Quarts (87 ft² each)
- 10
- Five-gallon pails5 gallons each
- 1
- Materials + delivery$25–$70 / gallon · Sep 2026
- $75 – $210
- Installed (with labor)typ. $1,080
- $651 – $1,746
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Common room sizes, answered
- How Much Paint for a 8×10 Room?80 ft²
- How Much Paint for a 10×10 Room?100 ft²
- How Much Paint for a 10×12 Room?120 ft²
- How Much Paint for a 11×13 Room?143 ft²
- How Much Paint for a 12×12 Room?144 ft²
- How Much Paint for a 12×14 Room?168 ft²
- How Much Paint for a 12×16 Room?192 ft²
- How Much Paint for a 14×16 Room?224 ft²
- How Much Paint for a 15×15 Room?225 ft²
- How Much Paint for a 16×20 Room?320 ft²
- How Much Paint for a 20×20 Room?400 ft²
- How Much Paint for a 24×24 Room?576 ft²
How to calculate paint by hand
Gallons = [2 × (L + W) × H (+ L × W ceiling)] × coats × (1 + extra) ÷ 350
Worked example
- Wall area: 2 × (12 + 12) × 8 = 384 ft².
- Two coats: 768 ft²; plus 5% for touch-ups = 806 ft².
- Gallons: 806 ÷ 350 = 2.3 → 3 gallons (or 2 gallons + 2 quarts).
- With the ceiling (144 ft² × 2 coats = 288 ft²): 1,094 ft² → 4 gallons — buy a 5-gallon pail.
- 1 gallon, smooth primed wall
- 350–400 ft² per coat
- 1 gallon, textured or bare
- 250–300 ft²
- 12 × 12 room, walls, 2 coats
- ≈ 2–3 gallons
- Trim & doors, average room
- ≈ 1 quart per coat
Questions crews ask
How much paint do I need for a 12x12 room?
Walls are 384 ft² at an 8 ft ceiling; two coats is 768 ft², which is 2.2 gallons — buy 3 (or 2 gallons and 2 quarts). Add about a gallon for the ceiling at two coats, and a quart for trim.
How many square feet does a gallon of paint cover?
350–400 ft² per coat on smooth, previously painted drywall. Bare drywall, plaster, textured walls and dark-to-light colour changes bring it down to 250–300 ft². Sprayers use 20–30% more than rollers.
How many coats of paint do I need?
Two coats for any colour change or new drywall (after primer). One coat can work for a same-colour refresh with a quality paint-and-primer product. Dark reds and yellows often need three.
Do I subtract doors and windows?
Only large ones — a patio door or a picture window. A standard door is 20 ft² and a window 15 ft²; the paint you save roughly equals what the trim around them uses, so most estimators ignore them.
Should I buy gallons or a 5-gallon pail?
A pail costs about the price of 3½–4 gallons, so buy one when you need 4 gallons or more. It also guarantees one batch — colour can shift slightly between individually tinted gallons. Box (mix) gallons together if you buy several.