Paint coverage changes with the surface, color change, product, and application method. Use the calculator for the wall quantity, then make the product decisions below before purchasing.
01
Same-color refresh
Sound, previously painted walls are being recoated in a similar color.
Subtract measured openings
Use the label coverage
Plan the stated number of coats
Decision
A normal coverage input is reasonable, but keep enough of the same finish for touch-ups.
02
Dark-to-light change
A dark wall is changing to a much lighter color or the existing finish is uneven.
Keep primer separate
Test whether two finish coats are enough
Do not raise coverage to force a lower total
Decision
Compare a primer-plus-paint system with extra finish coats before choosing the cheaper-looking option.
03
Porous or repaired wall
New drywall, patches, texture, or porous masonry may absorb more coating.
Use product-specific coverage
Include repaired sections
Allow for roller and tray loss
Decision
Treat the result as a starting order and confirm the sealer or primer system with the manufacturer.
Read the result
Four checks before you order
Confirm the result is paintable wall area, not floor area.
Check that coverage is per coat and that the coat count matches the plan.
Compare the calculated gallons with the full can sizes actually sold.
Keep primer, ceiling paint, trim paint, and specialty coatings as separate orders.
Included here
✓ Four room walls
✓ Measured doors and windows
✓ Finish-coat coverage
✓ Full-can rounding
✓ Entered can price
Plan separately
+ Ceiling
+ Primer or sealer
+ Doors and trim
+ Repairs and caulk
+ Tools and protective materials
Common estimating errors
Using floor area
Measure wall perimeter and height; a 120 sq ft room can have far more than 120 sq ft of wall.
Counting coverage once
Multiply the wall area by the number of finish coats before dividing by coverage.
Mixing product lines
Coverage and sheen vary. Use the label for the exact paint being purchased.
Paint volume = wall area × number of coats ÷ product coverage
Full cans = round paint volume up to the next complete can
Example calculation
For a 12 × 10 × 8 ft room with 51 sq ft of doors and windows, two coats, and 350 sq ft of coverage per gallon, the estimate is about 3.5 gallons. Buying four 1-gallon cans provides a practical purchase quantity.
Planning tips
Use the coverage printed on the actual paint label.
Measure the combined area of doors and windows for a more accurate result.
Textured or porous walls and dramatic color changes may need more paint.
Common questions
Paint calculator FAQ
How much area does one gallon of paint cover?
Many interior paints cover roughly 350–400 sq ft per gallon for one coat, but the product label is the best value to use.
Should I subtract doors and windows?
Yes. Enter their combined area when you want a tighter estimate. For a quick buffer, you can leave the opening area slightly low.
Does the calculator include primer?
No. Primer coverage varies, so estimate it separately using the same wall area and the coverage printed on the primer label.