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 finish coats.
- Keep the 350 sq ft/gal planning default or replace it with the coverage listed by your selected paint product.
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 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.
How accurate is this estimate?
Gross wall area and the optional openings deduction come directly from your measurements. Coat count is your selected project plan, while coverage depends on the paint and surface. Treat 350 sq ft/gal as an editable planning default and 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 coats total 602 sq ft, or about 1.72 gal at the 350 sq ft/gal planning default; plan to buy 2 gal.
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 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.
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 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.