Paint Calculator
Estimate interior wall paint using room perimeter, wall height, 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. The calculator subtracts planning allowances for doors and windows, accounts for multiple coats, and lets you replace the coverage default with the rate on your paint.
- Measure room length, width, and wall height.
- Count doors and windows; default deductions are shown in the methodology.
- Enter the number of finish coats.
- Use the paint label’s coverage rate when available.
Formula and methodology
Gross wall area = 2 × (length + width) × height. Subtract 21 sq ft per door and 15 sq ft per window. Multiply by coats, divide by coverage in sq ft/gal, then round the purchase amount up to whole gallons.
Important: Coverage is approximate and varies by paint, surface condition, texture, color change, tools, technique, and product instructions.
Worked example
A 12 ft × 10 ft room with 8 ft walls has 352 sq ft of wall. After one door and two windows, 301 sq ft remains. Two coats total 602 sq ft, or about 1.72 gal at 350 sq ft/gal; plan to buy 2 gal.
Before you buy
- Measure unusually large doors and windows separately; the calculator uses fixed planning deductions.
- Primer is a separate product and is not included.
- Porous surfaces, heavy texture, spraying, and strong color changes can reduce effective coverage.
Frequently asked questions
Why is paint coverage editable?
Coverage differs by product and surface. The 350 sq ft/gal value is only a planning default; use the label value when available.
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 round up to whole gallons?
Paint is commonly purchased in whole-gallon containers. Actual package options vary, so compare the exact calculated need with available sizes.