Fence coating Calculator: measuring notes and method
Count faces, edges and rails
Fence length multiplied by height describes one flat face. Two faces, exposed rails, posts and edges may add coating area, while open gaps do not need coating.
Choose coverage for the timber
Use separate items for primer and finish, or for sections with different timber condition, so their consumption rates remain visible.
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
- 8 m²/L
- Container size
- 4 L
- Waste allowance
- 5 %
Coating required: 6.3 L
Imperial worked example
- Total surface area
- 258.3339 ft²
- Openings / excluded area
- 0 ft²
- Number of coats
- 2 coats
- Coverage per coat
- 325.9667 ft²/US gal
- Container size
- 1.0567 US gal
- Waste allowance
- 5 %
Coating required: 1.6643 US gal
Follow the calculation
- Net area = 24 − 0 = 24 m².
- Coat area = 24 × 2 = 48 m².
- Quantity = 48 ÷ 8 × 1.05 = 6.3 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