Painting
Paint Calculator
Estimate wall area and gallons of paint for a rectangular room using coats, coverage per gallon, and optional waste.
Painting
Calculator inputs
Paint Calculator Results
Results update in your browser as you edit inputs. They are planning estimates, not complete shopping lists.
Enter project dimensions to calculate material quantity.
Assumptions
- The room is treated as a rectangle.
- Doors, windows, ceilings, trim, and primer are not subtracted or added.
- Coverage per gallon should come from the paint label.
- For buying paint, use the rounded whole-gallon quantity or the container sizes available for your product.
- Any cost estimate uses only the unit price you enter. No store or local price data is used.
Formula
- Wall area = 2 x (room width + room length) x wall height.
- Coated area = wall area x number of coats.
- Gallons needed = coated area divided by coverage per gallon.
- Gallons with waste = gallons needed x (1 + waste factor).
Example calculation
Example: 12 x 12 room
A 12 ft by 12 ft room with 8 ft walls has 384 sq ft of wall area. Two coats at 350 sq ft per gallon need about 2.2 gallons before waste.
Common mistakes
- Forgetting to multiply by the number of coats.
- Using advertised coverage when a rough surface needs more paint.
- Comparing costs without entering your own local product price.
FAQ
Does this subtract windows and doors?
No. For a quick DIY estimate, it uses full wall area. You can adjust coverage or waste if your openings are large.
Does this include ceiling paint?
No. It estimates wall paint only.