Check the path
Your calculation audit
Every total is shown as a short sequence so you can see what was measured, deducted, adjusted and rounded.
- 01Awaiting valid measurementsComplete the fields above to reveal the formula path.
Decorating
Paint calculator
Work out paintable wall area, litres and tins with coats, coverage and waste made explicit.
Transparent formulaFormula v1.0 · paintable area × coats ÷ coverage × waste allowance
Scope boundary: Coverage is an estimate. Product, surface condition, texture and application method can change the result.
Measure clearly
Simple guidance
Measure wall faces rather than floor size. Deduct large doors and windows, set the number of coats, then use the coverage rate printed on the chosen product.
Worked example
Follow the same logic
A 4 m × 2.4 m wall less 1.8 m² of openings leaves 7.8 m². At two coats and 10 m² per litre, the base need is 1.56 L before waste.
Planning tipWrite down the product factor or pack size you used, so a later change is easy to trace.
Before you buy
Three quick checks
- 01
Measure paintable faces, including any separate feature wall.
- 02
Use the coverage figure on the exact product tin.
- 03
Set the coats before comparing tin sizes.
Quick answers
Useful to know
Should I deduct windows and doors?
Deduct large openings where the paint is not applied. Small areas can be left in when they reasonably balance cutting-in and touch-ups.
Why does the coverage rate matter?
Coverage varies by paint, surface, texture and application. The manufacturer’s stated rate is the best starting point for the selected product.
Review record
Transparent, source-ready method
Last reviewed: 15 October 2026. Formula version: v1.0. Source/review data to be added — Calculator.Shop does not present placeholder figures as an authoritative trade specification.