Paint Calculator
Enter your room size and how many coats you plan. We work out the exact wall and ceiling area, subtract doors and windows, and tell you how many gallons to buy — with a 10% waste margin so you don't run short.
Room size
🛒 Supplies worth having on hand
A short list of the gear that makes a room look painted, not patched. As an Amazon Associate we earn from qualifying purchases.
How to use the Paint Calculator
Buying too little means a mid-job store run; buying too much wastes money. Enter your room's:
- Length, width, and wall height — the tool computes total wall area.
- Doors and windows — subtracted so you don't buy paint for surfaces you aren't rolling.
- Coats — one for a refresh, two for a colour change, three for dark-over-light.
Reading your result — and why it matters for a painting side gig
The result is gallons needed, with about 10% added for edges and touch-ups. If you price painting as a paid side job, exact material cost is what protects your margin: quote the client the true paint cost plus your labour, never a guess. The same maths works whether you're painting your own place or billing a customer.
Frequently asked questions
How many square feet does a gallon of paint cover?
A gallon of typical matte wall paint covers about 350 square feet in one coat. Glossier and primer coats cover a little less. This calculator uses 350 sq ft/gallon and adds 10% for edges, cut-ins and touch-ups.
How much extra paint for a second or third coat?
Each extra coat multiplies the surface area by one. Two coats roughly doubles the paint; three coats triples it. Dark colours over light walls, and bare plaster or wood, often need an extra coat or a separate primer.
Should I subtract doors and windows?
Yes. The calculator removes about 21 sq ft per door and 15 sq ft per window from the wall area so you don't buy paint for surfaces you aren't rolling. Still buy a little extra — colour batches rarely match on a return trip.