Paint Quantity Calculator

Estimating paint is mostly simple arithmetic — area divided by coverage, times coats — but it hides two traps. The first is that "area" must be the paintable surface, not the floor plan: the perimeter times the wall height, the ceiling if you want it, then doors and windows subtracted. The second is that coverage always means per coat, and the label number assumes a smooth, primed, medium surface.

Paint Quantity Calculator turns either a measured area or a set of room dimensions into the litres and gallons you need, layer by layer. Choose your paint type and its coverage, set the number of top coats, add a primer coat, and read off per-coat litres, the total for the job and the cans to buy — in square feet or square metres.

Underneath is a guide to coverage per litre and gallon, how the coats stack up, and the surface factors that make paint do more or less work. Everything runs in your browser; nothing is uploaded.

• By area or by room: Enter a measured surface area, or let room length, width and height calculate the walls with doors and windows deducted.
• Coats built in: Set 1 to 5 top coats, or none — the litres multiply layer by layer automatically.
• Primer treated separately: Add a primer coat with its own lower coverage and its own litre total.
• Paint type library: Interior emulsion, satin, exterior, enamel and primer, each with realistic coverage per litre and per gallon.
• Coverage override: Enter the exact m²/L or sq ft/gal figure from your paint tin when you want precision.
• Metric or imperial: Areas in square feet or square metres; results always shown in both litres and gallons.
• Cans to buy: Rounded 4-litre (and gallon) can counts so you know exactly what to order.
• Ceiling and openings: Room mode paints the ceiling if you want it and subtracts every door and window entered.
• Wastage allowance: A default 10% covers cutting in, roller absorption and touch-ups.
• Reports & export: Copy or download the estimate as text, CSV or JSON.
• Learning guide: Coverage table, measuring method, coats and surface factors built into the tool.

1. Pick the input. Area mode if you have already measured, room mode if you have length, width and height.
2. Choose the unit. Feet or metres — the room fields follow it and the area converts automatically.
3. Enter the area or dimensions. In area mode type the paintable surface; in room mode add doors and windows to deduct.
4. Set the coats. Usually two top coats over a primer coat; less for a quick refresh, more for dark-to-light changes.
5. Select the paint type. The coverage changes per litre; or set a custom coverage from the tin label.
6. Toggle primer. Recommended on plaster, bare wood and metal.
7. Read the litres. Per coat, total for the job, primer, gallons and whole cans to buy all appear instantly.
8. Export the estimate. Copy or download as text, CSV or JSON for the shopping list.

Example 1 — Bedroom repaint. A 5 × 4 m room, 3 m walls, one door, one window: about 50 m² to paint. Two coats of interior emulsion at 11 m²/L plus one primer coat need roughly 9.1 L top coat and 6.2 L primer — three 4-litre cans in total.

Example 2 — Hallway walls. 120 sq ft of measured wall at two coats of satin (10 m²/L ≈ 6.1 L per coat?) — no: 120 sq ft ≈ 11.1 m² per coat, so two coats need about 2.3 L of satin plus 1.4 L primer, within a single gallon each.

Example 3 — Dark to light walls. Repainting a navy wall pastel needs three coats, not two. A 40 m² wall at 10 m²/L across three coats needs 12 L of emulsion — buy three 4-litre cans and expect the third coat to still be needed for an even finish.

Example 4 — Rough exterior render. A 90 m² rendered wall using exterior emulsion at 8 m²/L (rough surface) with two coats needs about 22.5 L — five 4-litre cans, where the same area on smooth plaster would take four.

Example 5 — Checking a painter quote. A quote lists 12 L of emulsion for a 55 m² living room at two coats. The calculator says 11.6 L including waste, so the number is credible — flag it only if the quote also lists 12 L of primer, which a primed plaster wall rarely needs.

• Buy the right tins: Litres, gallons and whole cans from a measured area or plain room dimensions.
• Layer-aware: Per-coat and total volumes with primer handled separately, matching how a painter actually works.
• Accurate to the surface: Doors, windows, ceilings and rough-surface factors all count instead of the floor area guess.
• Type and brand flexible: Coverage library plus a custom setting from the tin label.
• Switch units freely: Plan in feet or metres and still read litres and gallons side by side.
• Steps shown: Perimeter × height, openings deducted, coverage applied — the working is visible at every stage.
• Export the list: Text, CSV and JSON summaries drop straight into the shopping list.
• Free and private: No account, no watermark, nothing uploaded.