---
title: "Paint calculator — free, runs in your browser"
description: "How much paint a room needs, allowing for doors, windows and the number of coats. Free, no sign-up, and nothing you enter leaves your browser."
url: https://atoneplace.net/tools/paint-calculator/
site: "At One Place"
---

# Paint calculator

How much paint a room needs, allowing for doors, windows and the number of coats.

## How it works

Enter the room dimensions and this works out the wall area, subtracts doors and windows, and converts to litres or gallons at a realistic spread rate.

The spread rate is where estimates go wrong. Tin labels quote a best case on a smooth, sealed, similarly coloured surface \u2014 typically 12 to 14 m² per litre. Real walls take more. Bare plaster drinks the first coat, textured or previously unpainted surfaces need noticeably more, and a strong colour change often needs three coats rather than two. The default here is deliberately more pessimistic than the tin.

Two coats is the working assumption for a repaint in a similar colour. Going from dark to light, or covering bare plaster, plan for a primer or mist coat plus two topcoats.

Buying slightly over is the cheaper mistake. A part-used tin seals and keeps for touch-ups; running out mid-wall leaves a visible join, and a later batch may not match exactly.

> This tool runs entirely in your browser. Nothing you enter is sent to a server, logged or stored, and the page keeps working with the network disconnected.

## Common questions

### How much paint do I need for a room?

Roughly the wall area divided by 11 m² per litre, then multiplied by the number of coats. A typical 4 × 3 m room with 2.4 m ceilings needs about 6 litres for two coats.

### How many coats of paint do I need?

Two over an existing similar colour. Three, or a primer plus two, when covering bare plaster or making a large colour change.

### Why does the tin say it covers more than this calculator assumes?

Tin figures are a best case on smooth, sealed, similarly coloured surfaces. Porous, textured or bare surfaces absorb considerably more.

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## Sources

- Typical range compiled from manufacturer specifications — At One Place (/about/)