acalculator

How much siding do I need?

Type the total length and height of the walls, the gables, and the doors and windows. The siding calculator finds the area in squares and how many pieces of siding to buy.

Your numbers

Units
Pieces to buy
179

1,350 ft² of wall takes 179 pieces of siding (14.85 squares with waste).

Cartons
8
Area to side
1,350 ft²
Squares
13.5
Squares with waste
14.85
Covered by one piece
8.333 ft²

Pieces to buy: 179. 1,350 ft² of wall takes 179 pieces of siding (14.85 squares with waste).

How to calculate

Computes the siding a house needs: the wall and gable area less doors and windows, in squares, and the vinyl panels and cartons or fiber cement planks to buy, with waste.

Example with the default inputs (Total wall length 140 ft, Wall height 9 ft, Gables 2, Gable width 30 ft, Gable height 8 ft, Doors and windows 150 ft², Siding Vinyl, double 4 in (8 in exposure, 12 ft 6 in), Extra for waste 10%): 1,350 ft² of wall takes 179 pieces of siding (14.85 squares with waste).

Method: Area = wall length × wall height + gables × width × height ÷ 2 − doors and windows; squares = area ÷ 100 ft²; pieces = ⌈area × (1 + waste ÷ 100) ÷ (exposure × piece length)⌉; vinyl cartons = ⌈pieces ÷ 24⌉.

  • Walls are rectangles of one height; each gable is a triangle.
  • Vinyl double 4 in panels show 8 in and are 12 ft 6 in long, 24 to a carton (2 squares); fiber cement 8.25 in planks show 7 in and are 12 ft long. Other products: type the exposure and length.
  • Waste is 10% by default. Trim, corners, starter strip, J-channel and soffit are not counted.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Total wall length 140 ft, Wall height 9 ft, Gables 2, Gable width 30 ft, Gable height 8 ft, Doors and windows 150 ft², Siding Vinyl, double 4 in (8 in exposure, 12 ft 6 in), Extra for waste 10% gives Pieces to buy 179, Cartons 8, Squares 13.5, Squares with waste 14.85.Source: CertainTeed Monogram vinyl siding, double 4 in (https://www.certainteed.com/products/siding-products/monogram, retrieved 2026-10-01), sold 24 panels of 12 ft 6 in to a carton (https://builderswarehouse.com/certainteed-monogram-double-4-siding-126-24-carton.html): 24 × 8 in × 12.5 ft = 200 ft², 2 squares
  2. Total wall length 140 ft, Wall height 9 ft, Gables 2, Gable width 30 ft, Gable height 8 ft, Doors and windows 150 ft², Siding Fiber cement plank 8.25 in (7 in exposure, 12 ft), Extra for waste 10% gives Pieces to buy 213.Source: James Hardie HardiePlank lap siding (https://www.jameshardie.com/product-catalog/exterior-siding-products/hardie-plank-lap-siding/, retrieved 2026-10-01), 8.25 in × 144 in planks (https://www.lowes.com/pd/James-Hardie-8-25-in-x-144-in-HZ5-HardiePlank-Cedarmill-Lap-Siding/999968871) with a 7 in exposure
  3. Total wall length 100 ft, Wall height 8 ft, Gables 0, Doors and windows 0 ft², Siding Fiber cement plank 8.25 in (7 in exposure, 12 ft), Extra for waste 0% gives Pieces to buy 115, Squares 8.Source: James Hardie HardiePlank lap siding, 8.25 in plank with a 7 in exposure, listed at 14.3 pieces per square (https://www.lowes.com/pd/James-Hardie-8-25-in-x-144-in-HZ5-HardiePlank-Cedarmill-Lap-Siding/999968871)

How it works

With P the total wall length, H the wall height, G the number of gables of width w and height h, and O the area of doors and windows:

  • Area to side = P × H + G × w × h ÷ 2 − O.
  • Squares = area ÷ 100 ft²; squares with waste = area × (1 + waste ÷ 100) ÷ 100 ft².
  • Covered by one piece = exposure × piece length.
  • Pieces to buy = ⌈area × (1 + waste ÷ 100) ÷ covered by one piece⌉.
  • Cartons (vinyl only) = ⌈pieces ÷ 24⌉.

⌈x⌉ means x rounded up to a whole number. The area shows to 1 decimal in ft² (m² in Metric), squares to 2 decimals, and the area of one piece to 3 decimals, all rounded half up.

Products. The coverage comes from each maker's sizes, as named assumptions:

  • Vinyl, double 4 in: 8 in exposure, 12 ft 6 in panels, 24 panels a carton (200 ft², 2 squares).
  • Fiber cement plank 8.25 in: 7 in exposure, 12 ft planks (7 ft² each, 14.3 a square).
  • Other: type the exposure and the piece length.

Exact arithmetic. Each size is read as the exact decimal you typed, in the unit you typed it in (a feet-and-inches pair counts by its value in inches), and the product sizes are exact (8 in = 0.2032 m, 12 ft 6 in = 3.81 m). Every step is exact, so 800 ft² of 7 ft² planks is 114.29, rounded up to 115, and a whole number of pieces is never rounded up by mistake.

Assumptions

  • Walls are rectangles of one height; each gable is a triangle.
  • Waste is 10% by default, for cuts at corners, openings and gables.
  • Trim, corners, starter strip, J-channel and soffit are not counted.

Rules

  • Wall length 1 cm to 1,000 m; wall and gable height 1 cm to 100 m; gable width 1 cm to 1,000 m; gables 0 to 50.
  • Doors and windows 0 to 100,000 m²; exposure 1 mm to 2 m; piece length 1 cm to 20 m; waste 0% to 100%.
  • When the doors and windows add up to the whole area or more, there is no answer: "The doors and windows add up to at least the whole wall and gable area."

Worked examples by hand

A 40 × 30 ft house, vinyl. Walls 140 × 9 = 1,260 ft²; gables 2 × 30 × 8 ÷ 2 = 240 ft²; less 150 ft² of openings = 1,350 ft² = 13.5 squares. With 10% waste, 1,485 ft² = 14.85 squares. One panel covers 8 ÷ 12 × 12.5 = 8.333 ft², so 1,485 ÷ 8.333 = 178.2, or 179 panels; 179 ÷ 24 = 7.46, so 8 cartons.

The same house in fiber cement planks. 1,485 ÷ 7 = 212.1, so 213 planks.

800 ft² of planks, no waste. 100 × 8 = 800 ft² = 8 squares; 800 ÷ 7 = 114.29, so 115 planks.

Other questions people ask

How do I calculate how much siding I need?

Add up the wall area (total wall length × height), add each gable (width × height ÷ 2), and subtract the doors and windows. Add about 10% for waste, then divide by the area one piece covers. A 40 × 30 ft house with 9 ft walls, two 30 × 8 ft gables and 150 ft² of openings has 1,350 ft² to side.

What is a square of siding?

100 square feet of wall. 1,350 ft² is 13.5 squares, or 14.85 squares with 10% waste.

How many square feet does a box of vinyl siding cover?

A carton of double 4 in vinyl panels holds 24 panels of 12 ft 6 in with an 8 in exposure: 24 × 8 ÷ 12 × 12.5 = 200 ft², or 2 squares. Check the label: thick or specialty profiles may hold less.

How many fiber cement planks are in a square?

An 8.25 in plank laps to a 7 in exposure, so a 12 ft plank covers 7 ÷ 12 × 12 = 7 ft². A square takes 100 ÷ 7 = 14.3 planks.

What is exposure?

The height of a lap siding piece that shows once the next course overlaps it. It is less than the board width: an 8.25 in plank shows 7 in. Pick Other to type your own exposure and length.

Does the calculator include trim?

No. Starter strip, J-channel, corner posts, soffit and fascia are bought by the length of edges and corners, not by area.