Example 1
- 384 ft²
- 400 ft²/gal × 2 coats
- 1-gallon can
1.92 gal · 2 cans
How much paint for 384 ft² at 400 ft²/gal and 2 coats? 384÷400×2 = 1.92 gal (2 cans).
Paint Calculator
Enter length, width, and height of a rectangular room, plus coverage from the can in square feet per gallon. Walls are perimeter times height. The floor is not included. A 12×12 ft room with 8 ft walls is 384 ft²; at 400 ft²/gal and two coats that is 1.92 gal.
Results
Enter the length, the width, and the height. Then enter the coverage and the number of coats.
The calculator subtracts openings, divides by coverage, and multiplies by coats. Porous surfaces add 15% or 25%. Can size rounds packages up. Related: wall area, article how much paint for walls.
How the results are calculated
Walls384 ft²
Coverage400 ft²/gal
Coats2
Paint1.92 gal
The paint calculator finds the volume to buy. It subtracts openings from area, divides by coverage, multiplies by coats and by the surface factor. Coverage is square feet per gallon from the can label (or m² per liter in metric).
A 12×12×8 ft room is 384 ft² of walls; at 400 ft²/gal and two coats that is 1.92 gal (2 cans). At 400 ft², 350 ft²/gal, two coats, and 15% more paint, the result is 2.63 gal.
Enter length, width, and height, or choose “I know the area”. The ceiling adds L×W. Openings, surface type, can size, and price are optional. Empty openings mean zero.
Wall square footage alone lives on the wall-area page. Plaster and concrete are separate. The chart beside the result shows 0–15% contingency — it does not change the primary result.
Can counts round up. 1.92 gallons in 1-gallon cans is 2 cans. Two coats use twice the paint of one coat.
Enter 12, 12, and 8 with 400 ft²/gal and two coats: 1.92 gal. Then area mode 400 ft² with porous surface: 2.63 gal.
How to use this calculator
- Enter length, width, and height. A 12×12×8 ft room is 384 ft². Or choose “I know the area”, for example 400 ft².
- Enter coverage from the can and the number of coats. Two coats mean twice the paint.
- Optionally subtract openings, pick surface type, and enter a can size.
- Click Calculate. At 384 ft², 400 ft²/gal, two coats, and 1-gallon cans the result is 1.92 gal and 2 cans.
- Wall area alone lives on the wall-area page. Here the result is paint volume.
Formula
net_area = area − openings
volume = (net_area ÷ coverage) × coats × surface_factor
cans = ⌈volume ÷ can_size⌉
Room mode: walls = 2×(L+W)×H, optionally + L×W (ceiling). A 12×12×8 ft room at 400 ft²/gal and 2 coats: 384 ÷ 400 × 2 = 1.92 gal.
Paint for 384 ft² at 400 ft²/gal
Area ÷ coverage × coats × surface factor. 384 ft² at 400 ft²/gal and two coats is 1.92 gal (2 cans).
- ft²
- Net area. A 12×12×8 ft room is 384 ft² and 1.92 gal at 400 ft²/gal × 2.
- ft²/gal
- Coverage from the can. 400 ft²/gal on 384 ft² and two coats gives 1.92 gal.
- coats
- Volume multiplier. Two coats = ×2.
- surface
- 1.0 / 1.15 / 1.25. At 400 ft², 350 ft²/gal, and two coats, porous surface gives 2.63 gal.
Usage examples
Example 2
- 400 ft²
- 350 ft²/gal × 2 coats
- 15% more paint
- 1-gallon can
2.63 gal · 3 cans
400 ft², 350 ft²/gal, 2 coats, +15% surface → 2.63 gal (3 cans).
Example 3
- 400 ft²
- openings 40 ft²
- 350 ft²/gal × 1 coat
1.03 gal
400 ft² − 40 ft² openings, 350 ft²/gal, 1 coat → 1.03 gal.
Example 4
- 144 ft²
- 400 ft²/gal × 1 coat
0.36 gal
A 12 by 12 ft ceiling is 144 ft². 144 ÷ 400 = 0.36 gal for one coat. A second coat is 0.72 gal.
Example 5
- 800 ft²
- 250 ft²/gal × 2 coats
6.40 gal
An 800 ft² exterior at 250 ft² per gallon and two coats is 6.40 gal, and no openings are subtracted.
Example 6
- 200 ft²
- a 20 ft² door
- 350 ft²/gal × 2 coats
1.03 gal
After a 20 ft² door, 180 ft² remains. 180 ÷ 350 × 2 = 1.0286 gal. The calculator shows 1.03 gal.
Example 7
- 80 ft²
- 350 ft²/gal × 3 coats
- 1-gallon can
0.69 gal
80 ft² at 350 ft² per gallon and three coats is 0.6857 gal. The calculator shows 0.69 gal and rounds that up to 1 can.
Example 8
- 600 ft²
- 300 ft²/gal × 1 coat
- 25% more paint
2.50 gal
A very absorbent surface on 600 ft² at 300 ft² per gallon and one coat is 2.50 gal. Without the extra 25%, the same area is 2.00 gal.
Related calculators
Frequently asked questions
How do I calculate how much paint I need from area and coverage?
Divide net area by can coverage (ft²/gal), then multiply by coats and the surface factor. 384 ft² at 400 ft²/gal and two coats → 1.92 gal.
How much paint do I need for a 12×12 ft room with 8 ft walls?
About 1.92 gal at 400 ft²/gal and two coats. Walls are 384 ft² (perimeter × height). The calculator rounds 1.92 gal up to 2 one-gallon cans.
Is this only a wall-area calculator without gallons?
No. The result is gallons (and cans). Wall area alone lives on a separate construction card.
Does the result replace the can label or a store quote?
No. Coverage comes from the manufacturer label. The calculator turns your numbers into volume — it is not a store quote.
Is this a free paint calculator?
Yes. Enter area or room sizes, coverage, and coats, and you see gallons at once. No account required.
How is paint volume calculated?
The calculator subtracts openings from area, divides by coverage (ft²/gal or m²/L), multiplies by coats and by the surface factor. A 12×12×8 ft room at 400 ft²/gal and two coats is 1.92 gal.
What does coverage mean?
Square feet per gallon from the can label (or m² per liter in metric), not gallons per square foot. At 400 ft²/gal, one gallon covers 400 ft² in one coat. On 384 ft² and two coats that is 1.92 gal.
How do room dimensions work?
Walls = 2×(length + width)×height. Selecting the ceiling option adds length×width. The floor is not included. A 12×12 ft room with 8 ft walls is 384 ft².
When should I use “I know the area”?
When you already have the net area to paint. Enter that instead of room sizes. At 400 ft², 350 ft²/gal, two coats, and 15% more paint, the result is 2.63 gal.
How are openings subtracted?
From the area before dividing by coverage. 400 ft² minus 40 ft² at 350 ft²/gal and one coat is 1.03 gal. An empty field means zero.
What does surface type do?
It multiplies volume. Default = 1.0, new/porous = 1.15, very porous = 1.25. At 400 ft², 350 ft²/gal, and two coats, porous surface gives 2.63 gal instead of 2.29 gal.
How are cans counted?
Volume ÷ can size, rounded up. 1.92 gal in 1-gallon cans is 2 cans.
Does the waste chart change the main result?
No. The chart shows the same volume plus 0%, 5%, 10%, or 15% contingency beside it. The primary result stays without that contingency.
How is this different from wall area?
Here the result is paint volume. Wall area reports only square footage. Paste that area into “I know the area” mode.
Does a comma in 1.92 work?
Yes. 1.92 and 1,92 are the same volume. At 384 ft², 400 ft²/gal, and two coats the result stays 1.92 gal.
Knowledge sources
Paint volume comes from area and label coverage. Area and volume units below from NIST.
Page updated October 12, 2026.