How this calculator works
The deck floor contributes its top area. Railing mode adds four long faces of each rectangular rail or post and, optionally, each square baluster; end grain and concealed intersections are omitted. Steps add one tread and one riser per step. Divide the exposed area times coat count by the label coverage and add loss allowance. Measured railing area can replace the geometric model. Whole cans determine purchase cost.
Formula
stain = (floor + railing + step area) x coats x (1 + loss) / coverage; rail surface = 2(section width + height) x length; square post or baluster surface = 4 x width x exposed height.
Worked example
A 20 m2 floor with two coats at 10 m2/L needs 4 L before loss, or 4.4 L with 10% allowance. A 10 m2 floor plus 4 m2 of railing needs 2 L at 7 m2/L for one coat.
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Frequently asked questions
Are board undersides included?
No. The floor uses its top area only. Add any other exposed wood to a measured custom railing area or calculate it separately.
Can I use a US-gallon coverage label?
Yes. Select ft2 per US gallon. US and imperial gallons are different; the stain volume selector offers both.
Do all stains need two coats?
No. Follow the exact product instructions for coats, drying and preparation. Coverage also varies with the condition of the wood.