How Much Paint Do I Need for a Room?

For a rectangular room, wall area is 2 × (length + width) × height. A room 12 ft long, 10 ft wide and 8 ft high has 44 ft of perimeter and 352 sq ft of gross wall area. Using its 120 sq ft floor area instead would leave out most of the surface.

Break irregular walls into rectangles and add their areas. Treat ceilings separately using length × width; doors, trim and baseboards may need different products. The room calculator estimates wall paint only, not every painted surface in the room.

The tool subtracts 20 sq ft per door and 15 sq ft per window in imperial mode, or 2 m² and 1.4 m² respectively in metric mode. These are simplified allowances in this calculator—not measurements of your particular openings and not an exact unit conversion between modes.

For unusual windows, double doors or large glazed walls, measure the actual openings and check the net area yourself. The tool cannot recognize their size from a count. It also does not add a separate amount for paint left on brushes, rollers or trays.

Sherwin-Williams describes typical gallon coverage of about 350–400 sq ft, while noting that application and surface condition affect requirements. RenoPlanMaker uses 350 sq ft per US gallon in imperial mode and 10 m² per litre in metric mode. These are separate assumptions, not precisely equivalent rates.

Check the product’s stated spreading rate, required coats and primer instructions. Rough or absorbent surfaces may need different preparation and quantities. The calculator lets you customize paint price, but not coverage: if the label differs substantially, divide your total coat-area by the label’s rate manually.

Consider a hypothetical room 4 m long, 3.5 m wide and 2.4 m high, with one door and one window. Gross wall area is 2 × (4 + 3.5) × 2.4 = 36 m². Applying the tool’s deductions leaves 36 − 2 − 1.4 = 32.6 m².

For two coats, the total coverage requirement is 65.2 m². At the tool’s 10 m²/L assumption, 65.2 ÷ 10 = 6.52 L. The main result rounds up to 6.6 L; the purchase line rounds up to 7 L. Check available pack sizes: two 4 L cans would actually mean buying 8 L.

The paint-cost line multiplies the rounded purchase quantity by your selected unit price. It does not price every combination of available cans, tinting charges, primer, brushes or delivery. Enter the price per gallon or per litre—not the total price of a multi-litre can.

Keep the same finish and color specification across the order. Follow the manufacturer’s advice on mixing compatible cans and retaining leftovers for touch-ups. Label retained paint with the room, color and product, and follow its storage instructions rather than decanting it into an unsuitable container.

A quantity estimate cannot tell you whether a surface is safe to sand. For US homes built before 1978, EPA recommends lead-safe certified contractors for work that may disturb lead-based paint. Other countries have different histories and rules; check local guidance for your property.

If you suspect asbestos-containing material, stop disturbing it and arrange appropriate assessment. Follow the paint label for ventilation, protective equipment, cleanup and recoating. Do not substitute a generic mask recommendation for the product’s safety requirements.

Confirm the measured area, chosen product, coverage and number of coats before buying. Price primer separately if needed. Set aside time for repairs, drying and cleanup as well as rolling the walls; the cheapest can is not necessarily the least costly complete job.

After painting a test area, reassess coverage and appearance before committing to the whole room. Keep the original quantity note with the paint specification so a second room or future touch-up starts with useful information instead of another guess.