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

These are typical per-coat estimates; real coverage varies roughly two-fold with timber porosity, so check your product's data sheet.

• Wood Stain: 10 m²/L per coat: Sadolin Classic Wood Protection quotes up to 10 m²/L (more on smooth planed, less on sawn)
• Varnish: 15 m²/L per coat: a conservative figure; thinner application gives higher coverage
• Decking Oil: 6 m²/L per coat: deliberately conservative versus the 6.4-9.6 m²/L Cuprinol UV Guard and Ronseal Ultimate quote; grooved boards need roughly double
• Fence Treatment: 4 m²/L per coat: low end of Ronseal Fence Life Plus's 4-6 m²/L range, suited to absorbent rough-sawn timber

These rates are based on manufacturer data from Ronseal, Cuprinol, and Sadolin and are chosen conservatively so you do not under-order. Actual coverage depends heavily on the porosity and condition of the wood: new, untreated timber absorbs more product than previously treated wood, and rough-sawn timber absorbs significantly more than planed timber. Ronseal Fence Life Plus also specifies two coats on rough-sawn wood and three on smooth planed wood. Because the deck calculator uses the plan area (length × width), allow extra product for grooved or profiled deck boards.