Primer Coverage Calculator — How Much Primer Do I Need?
Calculate primer quantities for new plaster, bare wood, metal and previously painted surfaces. Uses UK standard coverage rates.
Enter the total area directly, or calculate from wall dimensions
Enter the total surface area that needs priming
Adds 10% extra for absorption variation and application losses
10% recommended for most priming jobs
Enter your supplier price for a cost estimate
How We Calculate This
Our primer coverage calculator divides your total area by the coverage rate for your chosen surface type, then multiplies by the number of coats. Coverage rates vary significantly between surface types because porous surfaces like new plaster absorb far more primer than smooth, sealed surfaces.
The formula
Litres needed = (Total area × Number of coats) ÷ Coverage rate per litre × Wastage factor
For example, priming 40 m² of new plaster (8 m²/L) with 1 coat: 40 ÷ 8 = 5.0 litres, plus 10% wastage = 5.5 litres. You'd need 3 × 2.5L tins.
Coverage rates by surface type
- New Plaster: 8 m²/L — high absorption, the plaster soaks up primer rapidly
- Bare Wood: 10 m²/L — varies by wood type, softwood absorbs more than hardwood
- Previously Painted: 12 m²/L — sealed surface requires less primer
- Metal: 14 m²/L — smooth, non-porous surface with minimal absorption
These rates are based on manufacturer guidelines from Dulux, Zinsser and Crown. The actual coverage depends on surface condition, porosity and application method. We recommend 10% wastage for brush/roller application.
Frequently Asked Questions
Related Calculators
Paint Coverage Calculator
Calculate how many litres of paint you need for walls and ceilings.
Wallpaper Calculator
Work out how many rolls of wallpaper you need for any room.
Wood Stain Calculator
Calculate wood stain or varnish needed for decking, fences and furniture.
Masonry Paint Calculator
Calculate exterior masonry paint for outside walls.
Ceiling Paint Calculator
Calculate paint needed specifically for ceilings with correct coverage rates.
Last updated: February 2026
All calculations are estimates. Verify with your supplier.