Paint Calculator (How Many Gallons)
Enter the wall area directly, or switch to room dimensions and let the calculator work it out. Doors and windows get subtracted automatically so you are not buying paint for space you will never roll.
Paint Calculator
Pick how you want to enter area, then set coats, doors, and windows. Coverage defaults to 350 sq ft per gallon — check your can for the exact number.
Doors are deducted at 21 sq ft each, windows at 15 sq ft each. Buy the next full gallon up — partial gallons are not sold. Estimates only; confirm coverage on your specific paint can.
How much paint do I need? The formula
Paint is sold by coverage per gallon, so the calculation is: paintable area × number of coats ÷ coverage rate, rounded up to the next whole gallon. Paintable area is your gross wall area minus doors and windows, since you are not rolling paint onto a doorway.
| Step | Example: 12×10 ft room, 8 ft ceilings |
|---|---|
| Gross wall area | 2 × (12 + 10) × 8 = 352 sq ft |
| Deduct 1 door, 2 windows | 352 − 21 − 30 = 301 sq ft paintable |
| Two coats | 301 × 2 = 602 sq ft to cover |
| Gallons (350 sq ft/gal) | 602 ÷ 350 = 1.72 → 2 gallons |
Coverage rates vary by paint line and surface texture — flat finishes on rough drywall can run closer to 300 sq ft/gallon, while a smooth wall with a quality roller can stretch past 400. Always check the label on the can you are actually buying.
Contractor Estimate Calculator (Excel & Google Sheets)
Turn gallons and labor hours into a priced, itemized painting estimate — materials, labor, markup, and profit, auto-totaled.
One coat or two?
Two coats is the standard for a color change or any wall that has seen a few years of wear — it evens out roller marks and gives true, even color. A single coat can work for a same-color refresh on a wall already in good shape, but most pros quote two coats by default so the finish holds up and the client is not calling back about patchy spots.
Price the job and invoice it clean
Once you know the gallons, price labor, prep, and materials with a painting estimate template, then bill the finished job with a painting invoice template that separates materials from labor.
Frequently asked questions
How much does a gallon of paint cover?
Most interior paints cover 300–400 sq ft per gallon per coat, with 350 sq ft as a common label average. Rougher surfaces and darker color changes can push coverage toward the lower end.
Do I subtract doors and windows from paint calculations?
Yes. A standard door is roughly 21 sq ft and a standard window roughly 15 sq ft. Subtracting them from gross wall area keeps you from over-buying paint.
How many coats of paint do I need?
Two coats is standard for a color change or an older wall. A single coat can work for a same-color touch-up on a wall already in good condition.
Is this paint calculator free?
Yes — free, no sign-up. Enter your area or room dimensions and read the gallons needed. Estimates only; confirm coverage on your specific paint can.