Interior Paint Calculator USA 2026
Paintable area = wall perimeter × ceiling height − doors and windows, divided by 350 ft² coverage per gallon, multiplied by the number of coats.
Interior Paint Calculator — the quick answer
Paintable area = wall perimeter × ceiling height − doors and windows, divided by 350 ft² coverage per gallon, multiplied by the number of coats.
Paint Calculator — instant results
Show calculation steps
- Gross wall area = 52 × 8 = 416 sq ft
- Openings = 1×20 + 2×15 = 50 sq ft
- Paintable area = 416 − 50 = 366 sq ft
- Gallons = (366 × 2) ÷ 350 = 2.09 gal
Get Materials or Professional Project Help
Turn your interior wall paint estimate into a shopping list, or compare vetted local pros — both free.
Buy the materials
Affiliate links — BuildMate may earn a commission at no extra cost to you.
Hire a pro
Matched with up to 3 licensed local contractors. No obligation, no cost.
What the Interior Paint Calculator works out for your interior paint job
Paintable area = wall perimeter × ceiling height − doors and windows, divided by 350 ft² coverage per gallon, multiplied by the number of coats.
Enter Room perimeter, Wall height, Doors and Windows and the interior paint calculator returns the quantities you need to order instantly — no signup, no spreadsheet and no install. Every figure updates as you type so you can test two or three interior paint scenarios before you commit to an order or a bid.
Interior paint numbers this page gives you
The output is written for a real supply run: quantities and figures you can hand to a supplier or drop straight into a bid for interior paint work.
- A planning figure for interior paint, with the waste or contingency allowance stated.
How to estimate interior paint step by step
The math behind this page is Paintable area = wall perimeter × ceiling height − doors and windows, divided by 350 ft² coverage per gallon, multiplied by the number of coats.. Nothing is hidden — the formula, the assumptions and the waste allowance are all printed on the page so you can re-check the result by hand.
Worked example: A 12×14 room, 8 ft tall = 52 × 8 = 416 sq ft. Minus 1 door + 2 windows = 366 sq ft. Two coats ÷ 350 ≈ 2.1 gal.
- Measure the interior paint area or run and write down Room perimeter, Wall height, Doors and Windows.
- Enter the figures above and read the interior paint result.
- Add the recommended waste allowance before you order.
- Save or download the estimate so your supplier and your crew work from the same numbers.
Interior paint searches this page answers
Homeowners, DIYers and contractors reach this interior paint page looking for the same handful of answers. Each of these is answered above with the formula shown:
- Interior paint calculator
- How much interior paint do I need
- Interior paint estimator online
- Interior paint quantity takeoff calculator
- Free interior paint calculator app USA
- Interior paint material calculator 2026
Before you order interior paint: quick checklist
- Re-measure the interior paint area once before ordering — a second check is cheaper than a second delivery.
- Keep the stated waste allowance in the order; cuts and breakage are normal on interior paint work.
- Confirm coverage or unit size with your actual supplier — interior paint pack sizes vary by brand.
More interior paint planning tools
Pair this interior paint estimate with the rest of BuildMate: a full calculator index, an AI planner that turns a plain-English description into a materials list, and step-by-step guides for the trade work itself.
Targeted searches: interior paint calculator · how much interior paint do I need · interior paint estimator online · interior paint quantity takeoff calculator · free interior paint calculator app USA · interior paint material calculator 2026
How the interior wall paint math works
Interior Paint Calculator — frequently asked questions
How much does a gallon cover?
Roughly 350 sq ft on primed drywall.
Do I need primer?
Yes on new drywall or drastic color changes.
How do I use the Interior Paint Calculator?
Enter Room perimeter, Wall height, Doors and Windows. The interior paint calculator instantly returns the quantities you need to order, along with the formula and every calculation step so you can verify the result.
How much interior paint do I need?
It depends on your measurements, so run the interior paint numbers above rather than using a rule of thumb. The calculator applies the standard trade formula plus a stated waste allowance, which is what stops you from coming up short mid-job.
What does the Interior Paint Calculator include in its result?
It reports the quantities you need to order. The underlying formula is Paintable area = wall perimeter × ceiling height − doors and windows, divided by 350 ft² coverage per gallon, multiplied by the number of coats..
Is the Interior Paint Calculator free, and does it work on mobile?
Yes — it's free, needs no account, and runs in the browser on phone, tablet and desktop. Nothing is installed and your saved interior paint estimates stay on your own device.
Planning estimate only, produced from the formula shown above with documented assumptions. Always confirm quantities with your supplier or contractor before ordering.