CalculationTime

Paint Coverage Calculator

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Your numbers, formula and explanation together

Paint Coverage Calculator: 39.4 litres. Paint Coverage Calculator uses the declared inputs to produce a transparent default result. Total wall length: 12 m; Wall height: 2.4 m; Doors/windows to subtract: 3 m²; Number of coats: 2 coats; primary comparison: 12 and 2.4.

Formula applied

The exact method behind this answer

CalculationTime keeps the method visible so the number can be checked instead of blindly trusted.

Paintable area = max(0, total wall length × wall height − openings). Coated area = paintable area × coats. Litres before allowance = coated area ÷ coverage per litre. Litres with allowance = litres before allowance × (1 + allowance percent ÷ 100).
  1. Apply the formulaPaintable area = max(0, total wall length × wall height − openings). Coated area = paintable area × coats. Litres before allowance = coated area ÷ coverage per litre. Litres with allowance = litres before allowance × (1 + allowance percent ÷ 100).39.4 litresPaint Coverage Calculator uses the declared inputs to produce a transparent default result. Total wall length: 12 m; Wall height: 2.4 m; Doors/windows to subtract: 3 m²; Number of coats: 2 coats; primary comparison: 12 and 2.4.

Your live breakdown

Current inputs in the calculation

These values come from the controls above and update when the calculator changes.

Total wall length
12 m
Add the widths of the walls being painted.
Wall height
2.4 m
Use the average paintable height.
Doors/windows to subtract
3 m²
Subtract areas you will not paint.
Number of coats
2 coats
Paint coverage rate
10 m²/L/coat
Check the paint tin or technical sheet; 10 m²/L is a planning example.
Allowance
10 %
Optional allowance for porous surfaces, roller loss, touch-ups and colour changes.

Resulting answer

39.4 litres

Paint Coverage Calculator uses the declared inputs to produce a transparent default result. Total wall length: 12 m; Wall height: 2.4 m; Doors/windows to subtract: 3 m²; Number of coats: 2 coats; primary comparison: 12 and 2.4.

Answer
39.4 litres
Live support
Paint Coverage Calculator uses the declared inputs to produce a transparent default result. Total wall length: 12 m; Wall height: 2.4 m; Doors/windows to subtract: 3 m²; Number of coats: 2 coats; primary comparison: 12 and 2.4.

Assumptions used

What this answer assumes

Coverage-rate estimate only. Round to available tin sizes after checking the product and surface.

  • Wall dimensions are entered in metres and openings are entered in square metres.
  • Coverage rate is a user-entered planning value from the paint tin, supplier page or technical sheet.
  • The calculator treats walls as flat rectangular surfaces and does not include ceilings, trim, textured surfaces or spray loss unless you add them through the inputs.
  • Allowance is not a manufacturer guarantee; porous surfaces, primer, strong colour changes and application method can change real paint use.

Master’s Tip

How to use the result well

Master’s Tip: check the coverage rate on the exact product and surface. Bare plaster, dark-to-light colour changes, rough render and spraying can use more paint than a neat room-area estimate, so round purchase quantities up to available tin sizes after the arithmetic is visible.

Printable record

What belongs in the saved calculation

Save the inputs, result, formula, assumptions, page URL and date together so the calculation can be reviewed later.

Total wall length
12 m
Add the widths of the walls being painted.
Wall height
2.4 m
Use the average paintable height.
Doors/windows to subtract
3 m²
Subtract areas you will not paint.
Number of coats
2 coats

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Copy a clean iframe version with the required CalculationTime attribution link built in.

Formula

Paintable area = max(0, total wall length × wall height − openings). Coated area = paintable area × coats. Litres before allowance = coated area ÷ coverage per litre. Litres with allowance = litres before allowance × (1 + allowance percent ÷ 100).

Worked example

Total wall area = 12 × 2.4 = 28.8 m². Subtract 3 m² of openings to get 25.8 m² paintable area. Two coats require 51.6 m² of coated area. At 10 m²/L, that is 5.16 L before allowance. With 10% allowance: 5.16 × 1.10 = 5.68 L.

Professional note

Master’s Tip: check the coverage rate on the exact product and surface. Bare plaster, dark-to-light colour changes, rough render and spraying can use more paint than a neat room-area estimate, so round purchase quantities up to available tin sizes after the arithmetic is visible.

Regional and unit assumptions

Standard or basis: this page uses transparent rectangular-area and coverage-rate arithmetic in SI metric units. It does not claim a paint manufacturer warranty, surface-preparation standard or trade certification.

Assumptions and limitations

Methodology & Accuracy

How this calculator is checked

CalculationTime pages are built around visible arithmetic: the formula, assumptions, worked example and practical limitations are shown so the result can be checked rather than simply trusted.

Formula used

Paintable area = max(0, total wall length × wall height − openings). Coated area = paintable area × coats. Litres before allowance = coated area ÷ coverage per litre. Litres with allowance = litres before allowance × (1 + allowance percent ÷ 100).

Standard or basis

Standard or basis: this page uses transparent rectangular-area and coverage-rate arithmetic in SI metric units. It does not claim a paint manufacturer warranty, surface-preparation standard or trade certification.

Where a calculator follows a named legal, trade or industry standard, that standard is cited visibly. Otherwise the page uses transparent general arithmetic and states its limits.

Master's Tip

Master’s Tip: check the coverage rate on the exact product and surface. Bare plaster, dark-to-light colour changes, rough render and spraying can use more paint than a neat room-area estimate, so round purchase quantities up to available tin sizes after the arithmetic is visible.

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Questions

How do I calculate how much paint I need?

Calculate paintable wall area, subtract doors and windows, multiply by the number of coats, then divide by the paint coverage rate in square metres per litre.

Should I subtract windows and doors?

Yes when they are significant. Enter their total area as openings to subtract so the paintable area is not overstated.

What coverage rate should I use?

Use the coverage rate printed on the paint tin or supplier technical sheet for the product and surface. The default 10 m²/L is only a planning example.

Does this include primer or ceilings?

No. It estimates wall paint only from the entered wall dimensions. Add primer, ceilings, trim or specialist coatings as separate calculations or adjust the inputs deliberately.

How much extra paint should I buy?

The allowance field lets you test extra percentage for roller loss, porous surfaces, touch-ups and colour change. Round final purchase quantities to real tin sizes after checking the product.

Calculation note

Paint estimating starts with measured surface area, but the real purchase quantity depends on coats, product coverage, surface condition and waste. Keeping each assumption visible helps a decorator, homeowner or estimator see why a litre number changed.

Surface area comes before litres

Paint is usually specified by how many square metres one litre can cover for one coat. That means the first estimate is not litres at all: it is the paintable surface area after obvious openings are removed.

Coats multiply the workload

A second coat normally covers the same surface again, so coated area is paintable area multiplied by the number of coats. Primer, sealer or undercoat may need a separate calculation because the product and coverage rate can differ.

Coverage rates are product and surface dependent

Manufacturer coverage figures are planning guides, not proof that every wall will use the same amount. Porosity, texture, colour change, roller type, spray method and touch-ups can all move the final quantity.

Sources and further readingDulux: How much paint do I need?Sherwin-Williams: Paint calculator guidance