Construction & Trades
Paint Calculator
Measure the room’s length, width and wall height, count the doors and windows, and choose how many coats you’ll apply. The calculator subtracts standard door (21 sq ft) and window (15 sq ft) openings, divides by the coverage on the can and rounds up to whole gallons so you buy enough in one trip. Contractors can use the cost line for material pricing on a bid.
Estimates only. Verify important figures against your own records before acting on them. See our disclaimer.
How to use the Paint Calculator
- Enter the room length, room width, wall height, doors and windows and the remaining inputs.
- Optionally add price per gallon — leave blank to skip.
- Read the highlighted result first, then the breakdown below it. Load the worked example to check the math by hand.
What this calculator includes
What you enter
- Room length
- Room width
- Wall height
- Doors
- Windows
- Coats
- Coverage per gallon
- Price per gallon (optional)
What you get back
- Gallons to buy
- Paintable wall area
- Gross wall area
- Paint cost
How this calculation works
Paint quantity is wall area times coats, divided by how far one gallon spreads.
- Gross area = 2 × (length + width) × height
- Paintable area = gross − doors × 21 − windows × 15
- Gallons = paintable area × coats ÷ coverage
- Round up to whole gallons
What the result means
Gallons to buy is rounded up from the exact need so you finish in one batch with consistent color.
Common mistakes and assumptions
- Forgetting the second coat.
- Using spray or textured-surface coverage optimistically.
- Leaving primer out on new drywall.
Worked example
A 14 × 12 ft bedroom with 8 ft walls, 1 door, 2 windows, 2 coats at 350 sq ft/gal.
- 1Gross = 2 × 26 × 8 = 416 sq ft.
- 2Paintable = 416 − 21 − 30 = 365 sq ft.
- 3365 × 2 ÷ 350 = 2.09 gallons → buy 3 gallons ($135), or 2 gallons plus a quart.
Frequently asked questions
- How much area does a gallon of paint cover?
- Usually 250–400 square feet per coat on smooth, primed walls. Rough or porous surfaces use more.
- Do I need two coats?
- Two coats is standard for even color, especially when changing colors. One may do for a fresh coat in the same color.
- How much paint for a 12 × 12 room?
- With 8 ft walls, one door, two windows and two coats, about 2 gallons.
- Should I include the ceiling?
- Calculate it separately — length × width — usually with ceiling paint.
Disclaimer
This calculator returns estimates based only on the values you enter. It does not account for taxes, financing terms, local regulations, or conditions specific to your operation, and it is not accounting, legal, tax, or investment advice. Confirm any figure that carries real cost before you rely on it.
Calculations run entirely in your browser and the numbers you type are never sent to us or stored. Read how Answerivo calculators are built or report a correction. About Answerivo.