Skip to content
CalcBelt

Siding calculator

Measure the walls and gables of a house and get the siding to buy in squares, vinyl cartons or fiber cement planks, with waste and a typical installed cost.

Units
Walls

Ground or foundation line to the eaves. Add the floors of a two-story house.

Gables

The triangles under a gable roof: usually 2, or 0 for a hip roof.

Eave line to the peak. On a 6/12 roof it's a quarter of the gable width.

Openings

20 sq ft each

15 sq ft each

sq ft

A garage door, a large window: width × height.

Siding
%

CertainTeed suggests 10%. Low-pitch gables waste more.

CertainTeed measures walls with the doors and windows in, which leaves you extra; James Hardie's chart takes them out. Untick the box to follow CertainTeed. Soffit, trim and corner posts are not included.

Siding needed

14.2 squares

1,425 sq ft with 10% extra. A square is 100 sq ft.

Cartons
8200 sq ft (2 squares) per carton
Walls
1,260 sq ft
Gables
225 sq ft
Doors and windows
−190 sq ft
Siding area
1,295 sq ftBefore waste

Cost estimate

per sq ft

Installed: $10,360 for 1,295 sq ft (range $3,885 to $15,540)

Typical US price $3 to $12 per sq ft (HomeGuide, Fixr, October 2026). Vinyl siding, materials and labor. Removing old siding is extra.

How it's calculated
  1. Walls: 2 × (40 ft + 30 ft) × 9 ft = 1,260 sq ft
  2. Gables: 2 × 30 ft × 7.5 ft ÷ 2 = 225 sq ft
  3. Openings: 2 doors × 20 sq ft + 10 windows × 15 sq ft = −190 sq ft
  4. Net: 1,295 sq ft; add 10% = 1,425 sq ft = 14.25 squares
  5. 1,425 sq ft ÷ 200 sq ft per carton = 7.12, rounded up to 8

Estimates use manufacturer data sheets and industry guides (sources). Check local codes and your supplier's figures before you order.

How to use the siding calculator

  1. Enter the house's length and width and the wall height from the bottom of the siding to the eaves.
  2. Enter the gable ends: how many, and the width and peak height of each triangle.
  3. Count the doors and windows, and add any large openings such as a garage door in square feet.
  4. Pick the siding and check the waste, then read the squares and the cartons or planks to buy.

How to calculate siding

Walls = 2 × (length + width) × wall height
Gables = number × width × height ÷ 2
Siding = (walls + gables − openings) × (1 + waste)
Squares = siding ÷ 100

Example: a 40 × 30 ft house with 9 ft walls, two gables 30 ft wide and 7.5 ft high, 2 doors and 10 windows.

  • Walls: 2 × (40 + 30) × 9 = 1,260 sq ft
  • Gables: 2 × 30 × 7.5 ÷ 2 = 225 sq ft
  • Openings: 2 × 20 + 10 × 15 = 190 sq ft
  • Siding area: 1,260 + 225 − 190 = 1,295 sq ft
  • With 10% waste: 1,424.5 sq ft, or 14.2 squares

That’s 8 cartons of vinyl siding at 200 sq ft a carton, or 204 planks of 8 1/4 in fiber cement lap at 7 sq ft a plank.

Gable height

A gable’s height comes from the roof pitch: half its width times the pitch, divided by 12. The 30 ft gable above, under a 6/12 roof, is 15 × 6 ÷ 12 = 7.5 ft. The roof pitch calculator finds the pitch if you don’t know it. CertainTeed suggests adding 1 ft to the measured gable height to allow for waste, and notes that low-pitch roofs make more waste.

Planks per square

James Hardie’s 12 ft lap planks cover their exposure in inches as square feet, so the planks per square (100 sq ft) are 100 ÷ exposure, before waste:

Plank width Exposure Planks per square
5 1/4 in 4 in 25
6 1/4 in 5 in 20
7 1/4 in 6 in 16.7
8 1/4 in 7 in 14.3
9 1/4 in 8 in 12.5
12 in 10 3/4 in 9.3

What’s not included

The calculator counts the siding itself, not soffit, corner posts, trim or house wrap. CertainTeed’s estimating page measures soffit as the eave width times its length. For a house that isn’t a simple rectangle, run the calculator for each section and add the results.

Questions and answers

How do I calculate how much siding I need?

Add the walls (perimeter × wall height) and the gables (width × height ÷ 2 for each), subtract the doors and windows, then add about 10% for waste. A 40 × 30 ft house with 9 ft walls and two 30 ft gables 7.5 ft high needs 1,295 sq ft, or 14.2 squares with 10% extra.

What is a square of siding?

100 square feet of wall, the same square used for roofing: NIST lists the building square as 100 sq ft. James Hardie's coverage chart counts in squares too, and Owens Corning packs its vinyl siding 2 squares to a carton.

How many boxes of vinyl siding do I need?

Divide the siding area, waste included, by the coverage on the carton. Owens Corning packs its vinyl siding 2 squares (200 sq ft) to a carton, so 1,424.5 sq ft needs 7.1, rounded up to 8 cartons.

How many Hardie planks are in a square?

It depends on the exposure. James Hardie's coverage chart lists about 14 planks of 8 1/4 in HardiePlank (7 in exposure) per square, 17 of the 7 1/4 in and 13 of the 9 1/4 in, rounded and before waste. Each 12 ft plank covers its exposure in inches as square feet, so the exact figure is 100 ÷ 7 = 14.3.

Should I subtract windows and doors?

James Hardie's chart starts from the area less openings, so the calculator subtracts them, at 20 sq ft per door and 15 sq ft per window. CertainTeed's method measures walls with the openings in, which counts their area as extra. Untick the box to follow CertainTeed.

How much does new siding cost?

Vinyl siding costs $4 to $12 per square foot installed according to HomeGuide, and $3 to $12 according to Fixr. Fiber cement runs $6 to $15 (HomeGuide) or $5 to $14 (Fixr). Removing old siding adds $0.70 to $2 per square foot, HomeGuide says.

What's the difference between 4 in and 5 in vinyl siding?

The number is the exposure of each course on a double panel. Owens Corning's Double 4 in panels show 8 in per panel and are 12 ft 6 in long; its Double 5 in panels show 10 in and are 12 ft long. Both come 2 squares to a carton, so the carton count stays the same.

How much siding do I need for a 2,200 sq ft house?

It depends on the walls, not the floor area: a 2,200 sq ft house could have one story or two, and the wall height, shape, gables and windows all change the total. Measure the walls and gables and enter them in the calculator.

Sources

Figures checked October 2026.