Primer Quantity
Free Primer Quantity calculator with clear step-by-step results.
About Primer Quantity
Primer is bought in whole cans but specified as coverage per litre, so the calculation is area ÷ coverage, uplifted for how thirsty the substrate is, then multiplied by the number of coats. Stated coverage is measured on a sealed, smooth panel; bare plaster, new render, MDF edges and sanded timber can absorb 20-50% more than the label suggests.
Formulas
Primer per coat
Litres per coat = area ÷ coverage × (1 + porosity allowance)
Cans to buy
Cans = ceil(litres per coat × coats ÷ can size)
Worked example
With the default values below, Primer Quantity returns Primer Required of 6.90. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Surface areaminimum 0 m²
- 60 m²
- Stated coverageminimum 0.1 m²/L
- 10 m²/L
- Number of coatsaccepts 1–5
- 1
- Porosity and loss allowanceaccepts 0–60 %
- 15 %
- Can sizeminimum 0.25 L
- 5 L
Results
- Primer Required
- 6.90 L
- Primer per Coat
- 6.90 L
- Cans to Buy
- 2 cans
- Total Area Coated
- 60.0 m²
Step by step
- 1Values used
- 2Primer per coat
- 3Cans to buy
- 4Primer Required= 6.90 L
- 5Primer per Coat= 6.90 L
- 6Cans to Buy= 2 cans
- 7Total Area Coated= 60.0 m²
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
- Follow the primer manufacturer's data sheet for substrate preparation, coverage, thinning, recoat times and ventilation. Some primers require personal protective equipment and specific disposal.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Follow the primer manufacturer's data sheet for substrate preparation, coverage, thinning, recoat times and ventilation. Some primers require personal protective equipment and specific disposal.
Frequently Asked Questions
Why is my real coverage worse than the label?
Label figures assume a smooth, non-absorbent surface and even application. Porous, textured or previously unpainted substrates absorb more, and roller application puts down more than a sprayer for the same visible result.
Do I need two coats of primer?
Usually one is enough on sound surfaces. Use two on bare plaster, over strong stains, or when priming a very dark colour before a light topcoat.
Can I thin primer to stretch it?
Only within the manufacturer's stated limits. Over-thinning reduces film build and defeats the sealing and adhesion the primer exists to provide.