How do you calculate the square footage of a deck?

Multiply the deck's length by its width in feet. A 16-foot by 12-foot deck is 192 square feet. For an L-shaped deck, split it into separate rectangles, work out each one, and add them together. Then add about 10% for board waste when ordering decking material.

How many deck boards do I need?

Convert square footage to linear feet. A 5.5-inch board with a 1/8-inch gap covers about 0.47 sq ft per linear foot, so linear feet needed ≈ area ÷ 0.47. A 192 sq ft deck needs roughly 409 linear feet, or about 449 after adding 10% waste. Divide by your board length to get the board count.

How much stain do I need for my deck?

Deck stain and sealer cover about 150 to 200 square feet per gallon, so divide your deck's square footage by that range. A 192 sq ft deck takes roughly one to two gallons for a single coat. Rough, weathered, or bare wood absorbs more, so round up and buy extra for a second coat.

Do you count stairs and railings in deck square footage?

No. Deck square footage is just the flat walking surface — length times width. Stairs, railings, and fascia are measured and ordered separately because they use different amounts of material. Calculate them on their own and add the results to your total board and stain estimates so nothing is left short.

Deck Square Footage Calculator

Formel & Anleitung

So wird gerechnet

A deck's area is length times width, just like a room. Odd shapes are handled by breaking the deck into rectangles at each corner and summing the pieces, then adding waste for the boards.

1Measure the length and width of the deck surface in feet.
2Multiply length × width to get the area of each rectangular section.
3For an L-shaped or multi-level deck, split it into rectangles, calculate each, and add them together.
4Add a 10% waste factor for board cuts (use 15% for diagonal or picture-frame patterns).

Deck surface (16 ft × 12 ft)	192 sq ft
+ 10% board waste	≈ 211 sq ft
Decking boards (211 ÷ 0.47)	≈ 449 linear ft
Stain (192 ÷ ~150–200 sq ft)	≈ 1–2 gallons

Genauigkeit & Annahmen

L-shaped and multi-level decks are split into separate rectangles so no area is double-counted.
A 10% waste factor is added to board totals for end cuts and off-cuts.
Diagonal, herringbone, and picture-frame layouts need about 15% waste instead of 10%.
Railings, stairs, and fascia are estimated separately — they aren't part of the deck surface area.

Wichtige Tipps & Regeln

A standard 5.5 in board with a ~1/8 in gap covers about 0.47 sq ft per linear foot, so linear feet needed ≈ area ÷ 0.47.
You can also estimate board count as total area ÷ the coverage of one full board (length × 0.47 ft).
Add 10% waste for straight decking and 15% for diagonal or picture-frame patterns.
Deck stain and sealer cover roughly 150–200 sq ft per gallon, so divide your deck area by that range.

How to calculate the square footage of a deck

A deck's square footage is simply its surface area — length times width, measured in feet. For a straightforward rectangular deck, measure the two sides, multiply them, and you're done: a 16-foot by 12-foot deck is 192 square feet. This single number drives everything downstream, from how much decking to order to how much stain you'll need to seal it, so it's worth measuring the actual deck rather than working from a plan that may have changed during the build.

Most decks aren't perfect rectangles, though. If your deck wraps around a corner of the house or steps down to a lower level, break it into separate rectangles at each corner, calculate the area of each one, and add them together. This is the same approach you'd use to measure flooring in an irregular room — clean rectangles are easy to measure accurately, while trying to eyeball an L-shape as a whole leads to mistakes. The calculator above handles the multiplication and waste factor once you enter each section.

From square footage to decking boards

Deck boards are sold by the linear foot, not the square foot, so you need to convert. A common 5.5-inch-wide board with a standard 1/8-inch gap between boards covers about 0.47 square feet for every linear foot of board. That means the linear feet of decking you need is roughly your total area divided by 0.47. For a 192-square-foot deck, that's about 409 linear feet before waste, or around 449 linear feet once you add 10%.

Always buy extra. A 10% waste factor covers the off-cuts at board ends and the pieces you'll inevitably ruin. If you're running boards diagonally or framing the perimeter with a picture-frame border, bump that to 15%, because angled cuts waste more material. Order boards in lengths that minimize seams across your joist spacing to keep waste down.

Estimating stain, sealer, and the rest of the project

Once you know the deck's square footage, estimating finish is easy: most deck stains and sealers cover 150 to 200 square feet per gallon on a smooth surface, though rough or weathered wood soaks up more. A 192-square-foot deck therefore takes roughly one to two gallons for a single coat — round up if the boards are older or you're applying two coats.

Remember that railings and stairs aren't included in the deck surface area, but they still need finishing and material of their own. Measure the stairs and railing separately and add them to your stain estimate so you don't come up short partway through the job.

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