How to estimate and apply deck stain
Measuring a deck for stain, why coverage rates vary so much, how many coats to plan, and the prep that makes the finish last.
Measuring the real surface area
Start with the floor: length times width gives the square footage of the boards you will walk on. Then account for the railing, which is easy to underestimate because its top rail, both faces, and every baluster all need coating. Allowing about 3 square feet of surface per linear foot of railing rolls all of that into one number. If your deck has stairs, a skirt, or built-in benches, measure those separately and add them so nothing is missed at the store.
Why coverage rates swing so widely
The same can of stain can cover 150 square feet on one deck and 350 on another. The difference is the wood. Rough-sawn, new, or sun-bleached boards are porous and drink the first coat, while smooth, dense, or previously sealed decking lets more sit on the surface. Semi-transparent and solid stains also spread differently from thin penetrating oils. Reading the coverage range on your specific can and entering the low end keeps you from running short.
Planning coats and timing
Two coats is the usual recommendation for even color and lasting protection, and the second coat should go on before the first fully cures so the two bond. Penetrating oils are the exception and are often a single flood coat wiped back to avoid a sticky film. Work in the shade with mild temperatures and no rain in the forecast for a day or two, staining a few boards end to end at a time to keep a wet edge and avoid lap marks.
Prep is what makes it last
Stain is only as durable as the surface under it. Clean the deck to strip dirt, mildew, and any failing old finish, then let the wood dry for a couple of dry days so it can actually absorb the new coat. Sand or brighten gray, weathered boards, and set or replace popped fasteners before you start. Good prep is the difference between a finish that sheds water for a few seasons and one that peels within a year.