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Paint and Wall Area Calculator

Use this paint and wall area calculator entirely in your browser.

ResultPaint required: 7.84 L

Gross wall area: 43.20 m²

Paintable area after openings: 39.20 m²

Coverage calculation: 39.20 m² × 2 coats ÷ 10 m²/L

Surface condition, application method, paint opacity, and manufacturer coverage can change the quantity required.

Calculations happen locally in your browser.

How to use this calculator

  1. Enter the labelled values and review the live result.
  2. Review the live result and use Copy result when you need to share it.

How the calculation works

The perimeter is multiplied by wall height, openings are subtracted, and paintable area is multiplied by coats and divided by the coverage entered.

Formula

Litres = ((2 × (length + width) × height − openings) × coats) ÷ stated coverage

Step-by-step calculation

  1. Enter the labelled values and review the live result.
  2. The perimeter is multiplied by wall height, openings are subtracted, and paintable area is multiplied by coats and divided by the coverage entered.
  3. Check the displayed result, then copy it if needed.

Worked example

A 5 m by 4 m room, 2.4 m high, with 4 m² of openings and two coats at 10 m²/L requires about 7.84 L.

Methodology and review

Who this is for

DIY users and estimators planning room paint.

Inputs and units

  • Room length and width
  • Wall height
  • Openings
  • Coats
  • Coverage

Method

Room perimeter is multiplied by wall height, entered openings are subtracted, and the result is multiplied by coat count and divided by the stated product coverage.

Worked example

A 4 m × 3 m room with 2.4 m walls has 33.6 m² gross wall area before openings.

Assumptions

  • The room is rectangular and the entered coverage applies to the chosen paint and surface.
  • Doors and windows are represented by the total opening area entered.

Common mistakes

  • Using floor area as wall area
  • Forgetting additional coats

Limitations

  • Surface porosity, colour change, application method, waste, and manufacturer recommendations can change paint use.
  • Round purchase quantities up to available container sizes after checking the product label.

How this tool was checked

Unit fixtures verify wall perimeter, opening subtraction, coat multiplication, and coverage division.

Reference sources

Related tools

Calculation review: 21 August 2026. Published by Goldwave Dynamics Limited. This is an internal product review, not an independent certification.

Risk guidance

From room size to paintable area

The calculator models four rectangular walls, subtracts the opening area you enter, and applies the number of coats. Ceilings, trim, alcoves, and irregular surfaces need separate measurements.

Use the product's stated coverage

Coverage varies with paint, surface porosity, colour change, tools, and application. Enter the manufacturer's coverage figure and confirm container sizes before buying.

Frequently asked questions

Does this tool send my inputs anywhere?

No. The interactive calculation runs in your browser and this site does not submit tool inputs to a backend.

How should I use the result?

Use it for early planning only. Verify measurements, definitions, current local requirements, and the complete design with the relevant authority and appropriately qualified professionals.

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