Primer quantity Calculator: measuring notes and method
Count primer applications separately
Use primer coverage and primer coat count, not the finishing paint’s settings. A surface that only needs local priming should use the primed area rather than the entire painted area.
CHECK A PRACTICAL EXAMPLE
Spot priming or the whole surface?
Suppose a product specifies one primer application at 8 m²/L, supplied in 1 L containers. Compare the treated area only.
6 m² local repairs
- Primer required
- 0.75 L
- Containers to buy
- 1
24 m² whole surface
- Primer required
- 3 L
- Containers to buy
- 3
The preparation specification determines which area needs primer. These hypothetical rates do not select a primer or establish that spot priming is suitable for a particular substrate.
Fixed comparison in metric units. Values are illustrative unless linked to a recorded project; changing the calculator above does not change this example.
Formula
Coating = (area − excluded area) × coats ÷ coverage per coat × (1 + waste ÷ 100). Containers are rounded up.
Product reference: Sherwin-Williams coverage guidance
Worked examples in metric and imperial units
Illustrative values match Reset example and stay fixed when you edit the calculator. Both columns describe the same calculation; converted inputs are rounded.
Metric worked example
- Total surface area
- 24 m²
- Openings / excluded area
- 0 m²
- Number of coats
- 2 coats
- Coverage per coat
- 7 m²/L
- Container size
- 4 L
- Waste allowance
- 5 %
Primer required: 7.2 L
Imperial worked example
- Total surface area
- 258.3339 ft²
- Openings / excluded area
- 0 ft²
- Number of coats
- 2 coats
- Coverage per coat
- 285.2209 ft²/US gal
- Container size
- 1.0567 US gal
- Waste allowance
- 5 %
Primer required: 1.902 US gal
Follow the calculation
- Net area = 24 − 0 = 24 m².
- Coat area = 24 × 2 = 48 m².
- Quantity = 48 ÷ 7 × 1.05 = 7.2 L. Divide by 4 L and round up for containers.
Unit conversions
Liquid conversions use US gallons (3.785411784 L), not UK imperial gallons (4.54609 L).
Reviewed 19 October 2026. How calculations are checked · Report a correction