Paint Calculator
Estimate interior wall paint using room perimeter, wall height, measured openings, coats, and your paint’s editable coverage rate.
Instant estimate · No sign-up · Your measurements stay in your browser
Project details
Enter your measurements
Enter your project measurements. Planning defaults are identified where used. After your first calculation, edits update the estimate automatically.
Project estimate
Results
Enter your measurements, then select Calculate.
How to use this calculator
Estimate wall paint for a rectangular room. Enter the combined measured area of doors, windows, or other unpainted openings when you want a deduction, then choose coats and the coverage rate for your paint.
- Measure room length, width, and wall height.
- Optionally measure and add the area of doors, windows, or other surfaces that will not be painted.
- Enter the number of coats planned for your project.
- Enter the coverage listed for the paint product you plan to use.
Formula and methodology
Gross wall area = 2 × (length + width) × height. Subtract the optional total openings area entered by the user. Multiply the remaining area by planned coats and divide by the entered product coverage. The whole 1-gallon container equivalent rounds the calculated gallons up.
Important: Coverage is approximate and varies by paint, surface condition, texture, color change, tools, technique, and product instructions.
How accurate is this estimate?
Gross wall area and the optional openings deduction come directly from your measurements. Planned coats are your selected project value, while coverage depends on the paint and surface and must be entered from the applicable product information. Confirm coverage and available container sizes for the product you will purchase.
Worked example
A 12 ft × 10 ft room with 8 ft walls has 352 sq ft of wall. After entering 51 sq ft of measured openings, 301 sq ft remains. Two planned coats total 602 sq ft. If the product lists 350 sq ft/gal, the calculated volume is about 1.72 gal, or 2 whole 1-gallon container equivalents.
Before you buy
- Measure only openings or surfaces that will not receive the paint being estimated; leave the field blank for no deduction.
- Primer, ceilings, and trim are separate and are not included.
- Porous surfaces, heavy texture, spraying, and strong color changes can reduce effective coverage.
Frequently asked questions
Why must I enter paint coverage?
Coverage differs by product and surface. Use the coverage listed for the paint you plan to buy rather than relying on a universal value.
What should I enter for total openings area?
Add the measured square footage of doors, windows, or other surfaces that will not receive this paint. Leave it blank or enter zero when no deduction is needed.
Does this include ceilings or trim?
No. The result covers the four walls of a rectangular room only. Calculate ceilings, doors, and trim separately.
Why show a whole 1-gallon equivalent?
It is a simple comparison that rounds the calculated gallons upward. Actual package options vary, so compare the calculated volume with the container sizes available for your product.