How to use this calculator
- 1Measure the width of every wall you will side and add them up, and measure the wall height from the bottom of the siding to the eaves. Or enter the total wall area.
- 2Add up the area of the windows and doors and enter it to take them off.
- 3If the house has gable ends — the triangles of wall under the roof — enter how many there are, their width and their height.
- 4Choose your product: a box of vinyl siding, a fiber cement plank, a metric cladding board or your own coverage. Keep 10 % extra unless you have a reason to change it.
The formula
- 01Wall area = total wall width × wall height
- 02Gable area = number of gables × width × height ÷ 2
- 03Area to cover = wall area + gable area − windows and doors
- 04Area to buy = area to cover × (1 + extra %)
- 05Squares = area to buy ÷ 100 ft²; boxes or boards = area to buy ÷ coverage, rounded up
A gable end is a triangle, so its area is half of width × height. In North America siding is sold by the square, which is 100 ft². Most horizontal vinyl siding comes in cartons of 2 squares, and a fiber cement plank covers its length times its exposure — a 12 ft HardiePlank fitted at 7 in exposure covers 7 ft². In Europe cladding boards are usually sold per piece or per m²; Cedral Lap boards need about 1.75 boards per m².
Windows and doors are taken off in full here. Many installers only subtract large openings, because the pieces cut out around small windows are rarely usable — the extra percentage covers that. CertainTeed suggests a 10 % waste allowance on large projects, and adding about a foot to the gable height to allow for waste.
Worked example
120 ft of wall, 8 ft high, plus 2 gables 24 ft wide and 6 ft high, minus 150 ft² of windows and doors, leaves 954 ft² to cover.
With 10% extra that is 1,049.4 ft²: 10.5 squares, or 6 boxes of vinyl siding.
Tips before you buy
- Check that every box of coloured siding has the same production or lot code; shades can vary slightly between runs.
- Vinyl siding moves with temperature. Nail it loosely in the centre of the slots and leave the gaps at trim that the instructions ask for.
- Cutting fiber cement makes silica dust. Cut outdoors with shears or a dust-reducing saw and follow the manufacturer's safety instructions.
- Measure each wall on its own and write it down — it's easy to miss a bay window, porch wall or chimney.
- Order trim at the same time: starter strip for the base, corner posts, J-channel around windows and doors, and soffit if you are replacing it.
Frequently asked questions
How do I calculate how much siding I need?
Multiply each wall's width by its height and add them up, add the gable triangles (width × height ÷ 2), take off windows and doors, then add about 10 % for waste. Divide by 100 ft² for squares, or by the coverage of one box or board.
How many square feet are in a box of vinyl siding?
Most horizontal vinyl siding comes in cartons of 2 squares, which is 200 ft². Some thicker or insulated profiles are packed 1 square per carton, so check the label before you order.
What is a square of siding?
100 square feet of wall. Like roofing, siding is priced and packed by the square in the US and Canada.
How many Hardie boards are in a square?
About 14–15 planks of 8¼ in lap siding at 7 in exposure, because each 12 ft plank covers 7 ft². James Hardie's coverage chart lists 14 planks for one square and 29 for two, before waste.
Should I subtract windows and doors?
Subtract large openings such as garage and patio doors. For small windows many installers subtract little or nothing, because the cut-out pieces are usually scrap. The calculator takes off whatever area you enter, and the extra percentage covers the rest.
How much extra siding should I buy?
About 10 % for a simple house, and more for one with lots of gables, dormers and corners. CertainTeed suggests a 10 % allowance for large projects.
Also searched as: vinyl siding calculatorcladding calculatorhow much siding do I needsiding squares calculatorhardie board calculatorweatherboard calculator
Sources
- CertainTeed: estimating vinyl siding (10 % waste allowance, measuring gables)
- CertainTeed 2024 Siding Collection catalog (Monogram vinyl siding: 2 squares per carton)
- James Hardie: HardiePlank lap siding product data and coverage chart
- Cedral: fibre cement facades fixing guide (Cedral Lap, 1.75 planks per m²)
Formulas last reviewed: September 30, 2026 ·How we check our formulas