Deck Cost Calculator: Price Per Sq Ft & Install 2026

How deck cost is worked out

A deck has two costs, not one: the decking and the permit. The area is the length times the width. The billable area is the area plus 10% extra for cuts and waste: boards are cut to fit the edges, and the offcuts are waste. The decking cost is the billable area times the decking rate, and the total adds the permit: $15,400.00 + $250.00 = $15,650.00.

At the defaults — 20 by 20 ft, decking $35.00/sq ft, permit $250.00, 10% extra — the area is 20 × 20 = 400.00 sq ft, the billable area is 400 × 1.10 = 440.00 sq ft, the decking is 440.00 × $35.00 = $15,400.00, and the total is $15,650.00 — which is $15,650.00 ÷ 400 = $39.13/sq ft all-in.

The worked example, line by line

Setup: 20 by 20 ft, decking $35.00/sq ft, permit $250.00, 10% extra.

Line 1 — the area. 20 × 20 = 400.00 sq ft.

Line 2 — the billable area. 400 × 1.10 = 440.00 sq ft to order.

Line 3 — the decking cost. 440.00 × $35.00 = $15,400.00.

Line 4 — the total. $15,400.00 + $250.00 permit = $15,650.00.

Line 5 — the cost per square foot. $15,650.00 ÷ 400 = $39.13/sq ft all-in.

Line 6 — the budget. A $10,000 budget minus the $250 permit is $9,750, and $9,750 ÷ 38.5 = 253.25 sq ft of deck. A $20,000 budget buys 512.99 sq ft.

Every branch, checked

15 by 20 ft: the area is 15 × 20 = 300.00 sq ft, the billable area is 300 × 1.10 = 330.00 sq ft, the decking is $11,550.00 and the total is $11,800.00, or $39.33/sq ft all-in. A smaller deck costs less in total, but a little more per foot, because the $250 permit is spread over fewer feet.

Decking $25.00/sq ft: the billable area is the same, but the decking falls to 440.00 × $25.00 = $11,000.00, so the total is $11,250.00, or $28.13/sq ft all-in. Cheap decking is the boards and the yard, not the laying: pressure-treated pine is the same boards to lay as composite.

Extra 0%: with no extra for cuts and waste, the billable area is the area itself: 400.00 sq ft, so the decking is $14,000.00 and the total is $14,250.00, or $35.63/sq ft all-in. Ordering no extra saves $1,400.00 on paper, but the last board comes up short.

No permit: with no permit charge, the total is the decking alone: $15,400.00, or $38.50/sq ft all-in. Some towns charge nothing for a low deck, but a deck over 30 in high almost always needs one — check before you build.

10 by 12 ft: the area is 10 × 12 = 120.00 sq ft, the billable area is 120 × 1.10 = 132.00 sq ft, the decking is $4,620.00 and the total is $4,870.00, or $40.58/sq ft all-in. A small deck costs the most per foot, because the $250 permit is spread over only 120 feet.

Reverse — the $10,000 budget: the permit takes $250 of the budget, leaving $9,750, and $9,750 ÷ 38.5 = 253.25 sq ft of deck. A $20,000 budget buys 512.99 sq ft, which is 259.74 sq ft more than the $10,000 budget. The per-foot cost of 38.5 is 1.10 × $35.00 of decking.

What the defaults assume

The model assumes a flat deck on level ground: a deck on a slope, a deck with a diagonal pattern, or a deck with stairs changes the cuts, because the boards are cut to fit and the offcuts are waste. It assumes the decking rate includes the boards, the joists and the labour, which is right for a builder quote but not for boards bought alone. It assumes the permit is one flat fee: a town that charges by the square foot will charge more for a bigger deck. It assumes the deck is 30 in high or less for the permit note; a taller deck needs railings, which this model does not count. It leaves out the railings, the stairs, the footings, the sealing, and tax — ask the builder whether the quote includes those. Rounding convention: money is rounded to cents, areas to 2 decimals, and all figures are computed from unrounded values, rounded only for display.

Output · formula · meaning

Who uses this

• The homeowner replacing a rotting deck: they learn a 20 by 20 ft deck costs $15,650.00 — $15,400.00 of decking and $250.00 for the permit — so they know the exact number before they call the builder, and they know it is 440.00 sq ft of boards, not a guess.
• The landlord decking a rental yard: they learn a 15 by 20 ft deck costs $11,800.00 — and they learn the permit is $250 of $11,800, so building the deck in one go is cheaper than two small decks.
• The couple choosing between a deck and a patio: a deck costs $15,650.00 for this yard, and the same yard in pavers is cheaper to build — so they check the deck vs patio comparison before they decide, because a deck is dearer to build and dearer to keep.
• The renovator on a $10,000 budget: they learn $10,000 covers 253.25 sq ft — so they know the 400 sq ft deck is out of reach, and the 300 sq ft deck fits with room to spare.

Accuracy & limitations

The math is exact for the numbers you enter: the area is the length times the width, the billable area is the area plus the extra, the decking is the billable area times the rate, and the total adds the permit. What the model cannot do is measure your deck for you: measure along the deck, and for a deck that follows a slope or a diagonal, measure the deck, not the straight-line distance. It leaves out the railings, the stairs, the footings, the sealing, and tax — ask the builder whether the quote includes those. It assumes the decking rate includes the boards, the joists and the labour, and that the permit is one flat fee. It assumes the deck is built the season the boards arrive: boards left in a pile warp, and the extra you ordered does not cover boards that warped. For the deck against a patio, see deck vs patio cost; for the patio itself, see paver patio cost calculator.