Paint
Primer or sealer quantity and tins
- where
- primer needed (L)
- area to prime (m²)
- number of coats
- spreading rate (m²/L)
- waste and touch-up allowance (%)
- tins to buy
- tin size (L)
Explain this equation
Works out how much primer or sealer to buy and how many tins.
Area times coats divided by the spreading rate gives the litres, plus the waste allowance. Dividing by the tin size and rounding up gives whole tins.
Coverage arithmetic: litres equal area times coats divided by spreading rate.
Sense check: 40 m² at 20 m²/L with 10% waste needs 2.2 litres, one 5 litre tin with 2.8 litres left.
Watch out: porous surfaces such as bare plaster, MDF or old render can drink far more primer than the data sheet suggests.
Works out primer, sealer or stabiliser for bare or problem surfaces, and the number of tins of one size.
Enter your values to see the result.
Good to know
Spreading rates vary a lot by product: Farrow & Ball Masonry & Plaster Stabilising Primer is 100 m² per 5 L (20 m²/L); Crown Trade Fastflow Quick Dry Primer Undercoat up to 15 m²/L. Bare timber, MDF and porous masonry absorb more than the figure suggests. BS 6150 sets out when a primer, sealer or stabilising solution is needed for each background.
Common mistake
Skipping the primer on bare timber, metal or powdery surfaces to save time, which leads to poor adhesion of everything above it.
Limits
One tin size only. For mixed tin sizes use the paint quantity calculator.
Sources
- Farrow & Ball, How much paint do I need? (coverage per tin, e.g. Estate Emulsion 70 m² per 5 L; Masonry & Plaster Stabilising Primer 100 m² per 5 L; one primer & undercoat plus two topcoats)
- Crown Trade Fastflow Quick Dry Primer Undercoat technical data sheet (up to 15 m²/L depending on texture and porosity; 1, 2.5, 5 L)
- BS 6150:2019 Painting of buildings. Code of practice
Results are calculations from the published methods and figures shown, and depend on the data you enter. Coverage depends on the product, surface and application. Always follow the paint and wallcovering manufacturers’ data sheets and BS 6150 / BS 8000-12. Check prices and VAT with your own records and HMRC.