A deck is more than its floor — railings, stairs, posts, and the underside all add up
The floor is only the start. A spindled railing coats every side of every baluster (~1.8× its face), stairs add a tread plus a riser per step, posts get all four sides, and staining the underside + joists roughly doubles the floor. Measure only the floor and you under-buy.
What this diagram shows
A deck drawn in elevation showing the surfaces a stain estimate must include beyond the floor. The floor itself is length times width. A spindled railing must be coated on every side of every baluster plus the top and bottom rails, so it adds about 1.8 times its face-band area. Stairs add a tread plus a riser for every step. Support posts are coated on all four sides. Staining the underside and the joists roughly doubles the floor area because the rough lumber has twice the surface. A numbered key ties each part of the deck to the breakdown. Measuring only the floor badly under-buys stain.
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