Paint calculator
Paint Calculator
Estimate paint gallons from room dimensions, wall height, coat count, and coverage per gallon.
When to use this calculator
Use this calculator before buying paint for a bedroom, living room, rental refresh, office, hallway, or small renovation. It helps prevent both overbuying and running out mid-project.
Paint quantity depends heavily on surface condition, color change, primer use, roller type, and whether the wall is smooth, rough, patched, or porous.
Formula used
Wall area = 2 × (length + width) × height. Paint needed = wall area × coats ÷ coverage per gallon.
The formula is intentionally simple so it can be used for quick planning. Real bills, quotes, and installation costs can include fixed fees, taxes, tiers, labor, product limits, and site-specific conditions that a calculator cannot see.
Input guide
| Input | How to use it |
|---|---|
| Length, width, height | Measure the room in feet. Use wall height, not ceiling height assumptions. |
| Coats | Use two coats for most repainting jobs unless the product or color change says otherwise. |
| Coverage | Use the coverage printed on the paint can for the specific product. |
| Waste margin | Add margin for roller loss, touch-ups, uneven walls, and measurement errors. |
Examples
Standard room
A 12 × 12 ft room with 9 ft walls has about 432 sq ft of wall area before subtracting openings.
Two-coat job
At 350 sq ft per gallon, two coats on 432 sq ft needs about 2.5 gallons before waste and surface adjustments.
How to get a more accurate result
- Subtract large doors and windows only if you want a tighter estimate.
- Increase paint for rough texture, dark-to-light color changes, or damaged walls.
- Keep leftover paint for touch-ups if the color must match later.
Common mistakes to avoid
- Using floor area instead of wall area.
- Forgetting the second coat.
- Assuming every paint brand covers the same area.
Quick checklist before relying on the result
- Measure wall dimensions.
- Choose paint and read coverage.
- Decide primer and coats.
- Add a practical waste margin.
FAQ
Should I subtract windows and doors?
For small rooms it is optional. For large openings, subtracting them makes the estimate closer.
Do I need primer?
Primer may be needed for stains, repairs, raw drywall, major color changes, or glossy surfaces.
Why buy a little extra?
Touch-ups later look better when you have the original paint batch or product available.