Siding Calculator

How it works

gross area = perimeter × wall height (or Σ wall length × height) + Σ gable base × height ÷ 2 · net = gross − doors and windows · order = net × (1 + waste%) · squares = order ÷ 100 · vinyl boxes = order ÷ box coverage (usually 200 sq ft) · lap boards = order ÷ (exposure ÷ 12 × board length) · courses = wall height ÷ exposure, rounded up · corner posts = corners × ⌈height ÷ 10 ft⌉ · J-channel = opening edges + gable rakes

Siding is estimated in squares of 100 square feet, the same unit as roofing. Start from the wall area: the perimeter times the wall height, or each wall's length times its height, plus every gable triangle at half its base times its height. Subtract the doors, windows and garage doors you will not side over, either as one total area or by counting them with their sizes. A waste allowance covers the offcuts around openings and corners. Vinyl comes in boxes that usually cover two squares. Lap siding and fiber cement planks are counted from the board's exposure (the visible face) times its length, and panel siding by the sheet. Trim follows the edges: a corner post for every outside and inside corner, starter strip along the base, J-channel around openings and up the gable rakes, and undersill trim below the windows. Labor, when you add it, is priced per square of wall.

Worked example

A house with 140 ft of perimeter and 9 ft walls has 1,260 sq ft of wall. Taking off 180 sq ft of doors and windows leaves 1,080 sq ft, and 10% waste brings it to 1,188 sq ft, or 11.88 squares. That is 6 boxes of vinyl at 2 squares per box, and at $300 a square the siding costs $3,564. Four outside corners need 4 corner posts, the 140 ft base takes 13 pieces of starter strip, and the openings take about 17 pieces of J-channel and 4 of undersill trim.

Sources: Inch Calculator — siding squares, vinyl trim and lap-board exposure rules · Omni Calculator — siding area with doors, windows and waste

Frequently asked questions