Paint Calculator
Enter your dimensions for an instant answer — the exact quantity to buy (waste included), a material cost, and an estimated installed cost. Change any figure to update the result live.
| ITEM | QTY | PRICE RANGE |
|---|---|---|
| gallons | 3 | $84–$180 |
| Estimated material total | $84–$180 |
How much paint do I need?
Add up the square footage you are painting — for a room's walls, perimeter × ceiling height; add length × width if you are painting the ceiling too. The same math covers interior walls, ceilings and exterior siding: the calculator multiplies area by coats, divides by coverage, and rounds up to whole gallons.
Coverage is about 350 square feet per gallon per coat on smooth surfaces; textured or porous surfaces drink more. Two coats is the standard for an even finish, so most rooms land at 2–3 gallons.
Formula & methodology
gallons = (area ft² × coats) ÷ 350 ft² per gallon, rounded up
Area × coats ÷ coverage, rounded up to whole gallons. We deliberately skip a waste factor — the round-up to full gallons is the buffer, and leftover paint is your touch-up supply.
All constants are published on the material reference; the full model is on the methodology page.
400 sq ft, 2 coats: you need 2.29 gallons (buy 3 with waste), about $84–$180 in materials. See how we calculate this →
Paint cost
Interior paint runs $28–$60 per gallon nationally; professional prep-and-paint labor is priced per square foot and varies by state.
paint cost by state →Frequently asked questions
How much paint do I need?
One gallon covers about 350 square feet per coat. Divide your wall area by 350, multiply by coats, and round up. The calculator does this automatically.
How much paint for a 12×12 room?
A 12×12 room with 8-foot ceilings has about 384 sq ft of wall — 3 gallons at two coats. Painting the ceiling too adds 144 sq ft, taking it to about 4 gallons.
How much paint does a gallon cover?
About 350 square feet per coat on smooth, primed surfaces. Textured, porous or bare surfaces cover less — plan on 250–300 sq ft per gallon there.
How many coats of paint?
Two coats is standard for even coverage; three if you are covering a dark colour or bare drywall.
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