Wood Stain Calculator — How Much Stain, Varnish or Oil Do I Need?

Our wood stain calculator works by dividing your total surface area by the coverage rate of your chosen product, multiplied by the number of coats. You can enter the area directly or calculate it from fence panels, deck dimensions or furniture measurements.

The formula

Litres needed = (Total area × Number of coats) ÷ Coverage rate per litre × Wastage factor

For fence panels: Area = Number of panels × 1.83m × 1.83m × Number of sides

For example, 10 fence panels (one side) with fence treatment at 4 m²/L, 2 coats: Area = 10 × 3.35 = 33.5 m². Litres = 33.5 × 2 ÷ 4 = 16.75 L, plus 10% wastage = 18.4 L. You'd need 4 × 5L tins.

Coverage rates by product type

• Wood Stain: 10 m²/L — based on Ronseal and Sadolin product ranges
• Varnish: 15 m²/L — thin application gives higher coverage
• Decking Oil: 6 m²/L — grooved decking boards absorb heavily
• Fence Treatment: 4 m²/L — rough-sawn timber absorbs the most product

These rates are based on manufacturer data from Ronseal, Cuprinol, and Sadolin. Actual coverage depends heavily on the porosity and condition of the wood. New, untreated timber absorbs more product than previously treated wood. Rough-sawn timber absorbs significantly more than planed timber.