How to use the siding calculator
Whether you are cladding a new house in fibre cement, re-siding in vinyl or specifying timber weatherboards, the take-off always starts the same way: gross wall area, minus openings, plus waste. This calculator does that in one place and then turns the area into what you actually order, from squares or boards to the trim pieces that are easy to forget.
- Choose units. US mode takes feet for walls and inches for the exposure and gives squares; metric mode takes metres and millimetres.
- Enter the walls. Add up the length of every wall you are cladding for the perimeter, then enter the height from the bottom of the siding to the eaves and the number of outside corners.
- Add gables. Enter how many there are, their width and the rise from eaves to ridge. Enter zero for a hip roof.
- Enter windows and doors using a typical size for each, or zero to skip.
- Pick the siding type. For lap boards, enter the exposure and board length; for vinyl or sheet products, the area and squares are what you need.
Siding formulas
Gross area = perimeter × wall height + gables × ½ × gable width × rise
Net area = gross area − windows × w × h − doors × w × h
Order area = net area × (1 + waste %)
Squares = order area ÷ 100 ft²
Lap siding length = net area ÷ exposure × (1 + waste %)
Boards = ⌈lap siding length ÷ board length⌉
Corner trim = outside corners × wall height
J-channel = windows × 2(w + h) + doors × (w + 2h)
Starter strip = perimeter − doors × door width
House wrap goes over the whole wall before the siding, so the calculator gives it from the gross area with 10% added for laps. A common US roll is 9 × 100 ft, which covers 900 ft².
| Siding | Typical board or panel | Typical exposure |
|---|---|---|
| Fibre cement lap plank | 8¼ in × 12 ft | 7 in |
| Fibre cement lap plank | 6¼ in × 12 ft | 5 in |
| Cedar bevel siding | 1 × 6 (5½ in actual) | about 4–4½ in |
| Cedar bevel siding | 1 × 8 (7¼ in actual) | about 6 in |
| Vinyl double 4 in | panel about 12 ft long | 8 in per panel |
| Timber shiplap cladding | 125–150 mm board | the cover width, about 110–135 mm |
These are common sizes; the manufacturer's literature sets the exposure for the product you choose.
Worked examples
Fibre cement on a 30 × 40 ft house
The walls are 140 ft around and 9 ft high, which is 1,260 ft², and two 30 ft gables rising 7.5 ft add 225 ft², for 1,485 ft² gross. Twelve 3 × 4 ft windows and two 3 × 6 ft 8 in doors take off 184 ft², leaving 1,301 ft² net. With 10% waste, that is 1,431 ft², or 15 squares. With 8¼ in planks at a 7 in exposure, you need 2,453 linear ft, or 205 boards 12 ft long. Four corners at 9 ft give 36 ft of corner trim, and the openings need about 201 ft of trim or J-channel.
Timber cladding on a metric extension
A 10 × 8 m house with 2.7 m walls and two 8 m gables rising 2 m has 97.2 + 16 = 113.2 m² gross. Eight 1.2 × 1.2 m windows and one 0.9 × 2.1 m door take off 13.41 m², leaving 99.79 m², or about 109.8 m² with 10% waste. Shiplap boards with a 125 mm cover need 878 m of board, which is 183 boards 4.8 m long.
Who this calculator helps
- Architects checking cladding quantities for a cost plan or comparing materials at concept stage.
- Siding and cladding contractors building a quick quote and materials list.
- Builders and quantity surveyors cross-checking a supplier's take-off.
- Homeowners pricing a re-side or comparing vinyl, fibre cement and timber.
Practical tips
- Measure each elevation separately and add the walls up, especially on L-shaped houses with inside corners.
- Order the full quantity of a colour at once, since factory finishes and stains can vary between batches.
- Leave the gaps at trim and butt joints that the manufacturer calls for, and keep the bottom course clear of the ground.
- Get the gable rise with the roof pitch calculator, the paint for timber cladding with the paint calculator, and the glazing proportion with the window-to-wall ratio calculator.
Comparing cladding colours and materials with a client? Try them on a photo of the house with Exterior Redesign.
