Decorating & Walls calculator
Primer Calculator
Work out primer or sealer quantity from surface area, planned coats and the exact product coverage figure.
Work out primer or sealer quantity from surface area, planned coats and the exact product coverage figure. Enter the project measurements first, then replace any default material or performance value with data for the product you intend to use. Check coverage rate, coats and absorbency carefully. Primer coverage varies by substrate and formulation. Bare timber, plaster, metal and stain-blocking primers can have very different spread rates and coat requirements.
What you need to enter
The Primer Calculator uses the following project information to calculate the result.
- Area
- Number of coats
- Coverage per unit
- Extra allowance (%)
Calculator result
Required coating quantity, rounded buying quantity
How the Primer Calculator works
The Primer Calculator estimates required coating quantity, rounded buying quantity from this relationship: quantity = area × coats ÷ coverage × (1 + wastePct/100). Because the page is designed for primer or sealer before the finish coats, the calculation depends especially on coverage rate, coats and absorbency. Metric and imperial entries are normalised before the arithmetic so equivalent measurements produce equivalent results.
Primer Calculator worked example
Primer Calculator example: A 55 m² surface receiving one coat of primer rated at 9 m²/L needs about 6.11 L before allowance. Adding 10% gives roughly 6.72 L; porous new plaster, bare timber or masonry can require a different product rate. The important sense-check is coverage rate, coats and absorbency, because that can move the real requirement away from the neat theoretical result.
Important calculation assumptions
For primer or sealer before the finish coats, primer coverage varies by substrate and formulation. Bare timber, plaster, metal and stain-blocking primers can have very different spread rates and coat requirements.
Frequently asked questions
Do I need exact project measurements for the Primer Calculator?
To estimate primer or sealer before the finish coats, measure the surface area that will actually be coated, then enter the number of coats and the coverage figure printed for the exact product. Use measured or manufacturer-specific values wherever they are available.
What should I know about coverage rate, coats and absorbency before using the Primer Calculator?
For the Primer Calculator, use project-specific values for coverage rate, coats and absorbency. Primer coverage varies by substrate and formulation. Bare timber, plaster, metal and stain-blocking primers can have very different spread rates and coat requirements.
How should I turn the Primer Calculator result into an order quantity?
For the Primer Calculator, after calculating, round primer/sealer quantity up to the product sizes sold and follow the maker's substrate-specific application rate. Do not assume finish-coat coverage applies to primer.