Total linear feet of railing. Enter 0 if there is none.
Each step is counted as tread plus riser.
An estimate. Coverage varies with wood species, age, how dry the boards are and how you apply it. Always buy slightly more than the calculation, and mix multiple cans together so the colour is consistent across the deck.
Calculated entirely in your browser. Nothing you enter is sent anywhere.
How to use it
Measure the floor
Length times width in feet. This is the easy part.
Add the railing
Total linear feet. The calculator allows 4.5 sq ft per foot, covering both faces and balusters.
Match coverage to the wood
New smooth decking covers near the label rate. Weathered boards soak up far more.
How the calculation works
Deck floor area is straightforward. Railing is where most calculators fail: they ignore it or treat it as flat. In reality a railing has two faces, a top rail and a run of balusters, which works out to roughly 4.5 square feet per linear foot. On a deck with 40 feet of railing that is 180 square feet, more than a small deck floor.
Steps are counted as tread plus riser, which is why four steps on a wide deck adds meaningfully to the total.
Total surface is multiplied by coats and divided by the coverage rate. The second coat always uses less than the first because the wood is no longer absorbing at the same rate.
What this calculator does not do
It cannot know how thirsty your wood is. The rate on the can assumes smooth, prepared timber. A deck weathering for five years can take twice as much on the first coat.
It does not account for the underside, fascia boards or the posts below the frame.
It does not cover preparation. Cleaning, sanding and letting boards dry matters more to how the finish lasts than which brand you buy.
Questions
How much for a 16 by 12 deck?
Around 1.5 to 2 gallons for two coats of the floor alone. With railing and steps, roughly 3 gallons.
Do I need two coats?
Usually yes for semi-transparent and solid stains. Clear sealers are often one. Over-applying some products causes peeling.
Should I buy extra?
Yes, and mix the cans together first. Batch colour varies, and running out halfway leaves a visible line.
How long should wood dry?
At least 48 hours after cleaning, longer in humid weather. Staining damp wood traps moisture and the finish fails early.
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