Paint Calculator
Calculate paint needed for walls and ceilings, allowing for doors, windows and multiple coats.
Please note: Material estimates for planning only. Always confirm quantities against your drawings, local building codes and supplier specifications before ordering. Structural work requires a qualified engineer.
What the Paint Calculator does
Paint quantity is paintable area multiplied by the number of coats, divided by the coverage rate. Wall area is the room perimeter times the height, less the doors and windows you are not painting over.
Formula
Wall area = 2 × (Length + Width) × HeightCeiling area = Length × WidthPaintable area = Gross area − Door and window openingsLitres = Paintable area × Coats ÷ Coverage per litre
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Room length | number | Yes | Accepts more than 0. |
| Room length unit | one of 6 options | Yes | — |
| Room width | number | Yes | Accepts more than 0. |
| Room width unit | one of 6 options | Yes | — |
| Wall height | number | Yes | Accepts more than 0. |
| Wall height unit | one of 6 options | Yes | — |
| Surfaces to paint | one of 3 options | Yes | — |
| Number of doors | number | Yes | Accepts 0 or more. |
| Number of windows | number | Yes | Accepts 0 or more. |
| Area per door | m² | Yes | Accepts 0 or more. |
| Area per window | m² | Yes | Accepts 0 or more. |
| Number of coats | number | Yes | Accepts 1 or more. |
| Paint coverage | m² per litre | Yes | Check the tin — typically 10–13 m²/L for emulsion. Accepts 1 or more. |
| Price per litre | selected currency | Optional | Accepts 0 or more. |
| Currency | one of 10 options | Optional | — |
How to use it
- Choose Room length unit and Room width unit.
- Enter Room length, Room width, Wall height and Number of doors and 5 more.
- Optionally add Price per litre.
- Select Calculate.
Worked example
A 5 m × 4 m room, 2.4 m walls, walls only, 1 door, 2 windows, 2 coats, 11 m²/L coverage.
- Length
- 5 m
- Width
- 4 m
- Height
- 2.4 m
- Doors
- 1
- Windows
- 2
- Coats
- 2
Wall area 43.2 m², less 4.8 m² openings = 38.4 m². Two coats = 76.8 m² ÷ 11 = 7.0 litres.
Frequently asked questions
Do I need to deduct doors and windows?
For a small room the difference is minor and the extra paint is useful for touch-ups. For large glazed areas it matters and is worth deducting.
How many coats do I need?
Two is standard over an existing similar colour. Dark to light, or bare substrate, usually needs a primer plus two topcoats.