Carpentry Calculators

Siding calculator

Enter the walls, the gable ends and the openings. This works out the squares of siding, the lap boards or panels that covers at your exposure, and the starter strip, J-channel and outside corners that go with it.

Siding
ft

All the walls, end to end

ft

Bottom course to the soffit

ft
ft

Base to peak

in
in
in
in
in

The face left showing, not the board width

ft
ft
ft

The length it is sold in

%

10% is a common allowance; more for many openings

Squares of siding

10.38squares

Boards

149

Each board covers

7.00 sq ft

Net wall

944 sq ft

Name this job

Saved jobs stay in this browser. Nothing is sent anywhere, and a save is not a backup — a link is how you move one to another device.

Materials

Siding boards1038 sq ft with waste, 7.00 sq ft each
149
Starter strip120 ft along the bottom of the walls, plus waste
11 pieces
J-channel172.7 ft around the openings, plus waste — windows on four sides, doors on three
16 pieces
Outside corners32 ft — each corner its own full height, never spliced
4 pieces

Where the area comes from

Walls
960 sq ft
GablesWidth × rise ÷ 2 for each
144 sq ft
Less windows
120 sq ft
Less doors
40 sq ft
Net wall to side
944 sq ft

Inside corners, soffit, fascia, window trim and house wrap are not counted here. Buy siding for a whole job from one run where you can — a later batch can differ in colour.

Where to buy this

This searches the material, not a size or colour worked out for you — match the profile and colour of the siding you chose.

Plain search links, nothing sponsored. Prices and stock are the shop's, and a local lumberyard will usually beat both on solid stock.

About siding

What is a square of siding?
100 square feet of wall — the same square roofing is sold in. A 24' × 36' single-storey house with 8 ft walls, two 6 ft gables, ten windows and two doors comes to 944 sq ft of net wall, or 10.38 squares once 10% waste is on.
How much does one piece of lap siding cover?
Its length times its exposure — the part left showing — not its full width, because the rest is lapped under the course above. A 12' board at 7" exposure covers 7 sq ft, so the example house above takes 149 of them. A narrower exposure looks finer and buys more boards for the same wall.
How do I work out the area of a gable end?
It is a triangle: the width across its base times its rise from the base to the peak, divided by two. A gable 24 ft wide on a 6/12 roof rises 6 ft, so it is 24 × 6 ÷ 2 = 72 sq ft. Measure the rise rather than guessing it from the pitch if the roof overhangs or the gable sits above a band board.
How much J-channel do I need?
The perimeter of every opening: all four sides of a window, and both jambs and the head of a door, whose bottom is the threshold. Ten 36" × 48" windows and two 36" × 80" doors come to 173 ft, which is 16 twelve-foot lengths once 10% waste is on.

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