Paint Calculator
Estimate paint quantity, coverage, coats and project cost instantly — with engineering drawings and a printable PDF report.
Material cost estimate (optional)
How to estimate paint
Three simple steps to a complete paint and coverage estimate.
Interior wall, exterior wall, ceiling, full room or custom area — choose the mode so the right dimensions are asked for.
Add dimensions, doors and windows, coats, coverage rate and surface condition. Metric and imperial both work.
Total paintable area, paint required in gallons and litres, deducted openings, coats, wastage and optional cost — clearly broken down.
Paint Calculator — Free & Accurate
Our paint calculator helps homeowners, painters, contractors, and project planners estimate exactly how much paint a project needs. Pick a mode — interior wall, exterior wall, ceiling, full room, or custom area — enter the dimensions and openings, and get a complete paint estimate with coverage, coats, and cost in seconds.
The calculator uses your supplied coverage rate (default 350 sq ft per gallon — typical for emulsion paint on smooth surfaces) and adjusts it for surface condition: fresh and rough surfaces absorb more paint, while smooth repaints get better coverage. Door and window areas are deducted from the gross surface area to give a realistic paintable area. The math handles multiple coats and applies your chosen wastage buffer (0% to 15%) on top.
Results show paintable area, paint required in both gallons and litres, openings deducted, coats applied, effective coverage rate, and wastage allowance — plus an optional cost estimate including paint, primer, and labor in your local currency. Everything runs in your browser — no signup, no data sent to any server.
Why use this calculator?
Built for the site, not the spec sheet — simple, fast, and accurate.
No spreadsheets, no formulas to memorise. Type your sizes, hit calculate, and you're done.
Adjusts coverage for fresh vs repainted surfaces, deducts doors and windows, and handles multiple coats automatically.
Everything runs in your browser. Your dimensions never leave your device.
Mix metres, feet, inches, and centimetres on the same job — the math converts cleanly.
Tells you paintable area, gallons or litres needed, and exactly how many tins to buy — what your supplier needs to quote.
Open it on your phone right at the workshop. Fully responsive, no app needed.
Related construction tools
Free, browser-based, and built the same way as the paint calculator.
Frequently asked questions
Two coats is standard for most jobs — it gives even color and full opacity. One coat is enough only when you're going over a similar color with the same finish and the surface is in good condition. Three coats are needed when going from dark to light (covering a darker existing color), when applying rich saturated colors, or when painting porous surfaces that absorb paint heavily. The calculator multiplies the paint amount by the number of coats automatically.
We calculate the gross surface area (length × height for walls, length × width for ceilings/floors), then deduct the total area of all doors and windows you've added to get the paintable area. That paintable area is multiplied by the number of coats, divided by your coverage rate (with adjustments for rough or fresh surfaces), then increased by your wastage percentage. The result is in gallons or litres depending on the coverage unit you chose.
Most paint manufacturers state coverage on the can — typically 350–400 sq ft per gallon (8–10 m² per litre) for standard interior emulsion on smooth surfaces. Premium paints can reach 450 sq ft/gal. The actual coverage depends on surface condition: rough or fresh (never-painted) surfaces absorb 20–30% more paint, while smooth repaints can stretch the coverage a bit further. Pick the surface type that best matches your job and the calculator adjusts the rate automatically.
Yes — for an accurate quantity, deduct openings you won't be painting (windows, doors, vents). The calculator includes a deduction system: enter the count and pick a typical size. A standard interior door is around 1.6 m² (~17 sq ft), a standard window around 1.44 m² (~15 sq ft). For walls with lots of trim or trim that will be painted in a different color, you may want a separate calculation for the trim.
Yes. Every dimension has its own unit picker, so you can enter the wall length in feet, the height in metres, and the coverage rate in sq ft/gallon or sq m/litre on the same calculation. The math converts everything to consistent units internally.