Paint Coverage Calculator: measuring notes and method
Measure the faces being coated
Sum the actual surface areas receiving the same coating. For a door, decide whether one face, both faces and edges are included; floor area is not a substitute for coated area.
Different substrates need separate rates
Use separate items where the product or substrate changes. Combining unlike surfaces under one average coverage rate makes the estimate harder to check.
CHECK A PRACTICAL EXAMPLE
A door has more than one paintable face
An illustrative 2 × 0.8 m door has a 1.6 m² face. The comparison excludes edges and uses two coats at 10 m²/L.
One face
- Coating required
- 0.32 L
- Containers to buy
- 1
Both faces
- Coating required
- 0.64 L
- Containers to buy
- 1
Choose faces deliberately; the wall opening deduction does not account for painting the door itself. Include edges as a separate measured area when they receive the same product.
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
- 10 m²/L
- Container size
- 4 L
- Waste allowance
- 5 %
Coating required: 5.04 L
Imperial worked example
- Total surface area
- 258.3339 ft²
- Openings / excluded area
- 0 ft²
- Number of coats
- 2 coats
- Coverage per coat
- 407.4584 ft²/US gal
- Container size
- 1.0567 US gal
- Waste allowance
- 5 %
Coating required: 1.3314 US gal
Follow the calculation
- Net area = 24 − 0 = 24 m².
- Coat area = 24 × 2 = 48 m².
- Quantity = 48 ÷ 10 × 1.05 = 5.04 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