Deck stain calculator
Deck area is the easy part. The railing — two faces and a cap over its whole run — is usually a bigger surface than people expect, and the stairs add more. Put your product's own coverage figure in, because it is the number that actually decides how many cans you carry home.
Coverage on rough or weathered wood can be far below the label figure — the first coat on bare, thirsty timber drinks. Prices move weekly and by region. Enter the unit price your yard quoted you — the defaults are round placeholders, not a market average.
Why the railing is the surprise
A guard has an inside face, an outside face, a cap rail, and the balusters — which are all edges. Coating it properly is closer to four square feet per linear foot of run than to one, and on a deck with a guard round three sides that can rival the floor.
It is also the part that takes the longest, because it is all detail work with a brush. Budget the material and the day, and do the undersides while you are there — an unstained underside of a cap rail is a wet edge for twenty years.
Coverage is the number that moves
The label's coverage figure assumes smooth, prepared wood. Rough-sawn stock, weathered timber and bare thirsty boards can take substantially more, and the first coat on new wood is always the hungriest.
The practical rule: work out the first coat generously, then a second coat goes much further because the wood is already sealed. If you are staining one section as a maintenance coat rather than the whole deck, the second-coat figure is the right one.
Buy it all at once
Two cans of the same colour from different production batches are not identical, and the join shows across a deck floor in daylight. Buy the whole quantity in one purchase and box the cans — pour them together into a larger container and stir — before you start.
Round up. Running out three boards from the end forces a stop mid-run, and a lap mark on a deck floor does not sand out. A spare part-can is also what you want for touching up the cut ends and the odd board you replace later.
Then read the stain guide before opening anything — on new pressure-treated wood the water test decides whether today is the day at all.
Sources
Nothing here is asserted as a current figure. The tool is arithmetic on what you type, and every default is a round placeholder for your yard's quote.