Quick answer: siding needed = (wall area + gable area − windows and doors) × 1.10 for waste. Divide by 100 to get squares. Divide by (exposure in feet × piece length) to get the number of pieces.
How to measure a house for siding
Siding take-offs are simple geometry: rectangles for walls, triangles for gables, and holes for windows and doors. Walk around the house with a tape (or use the plans) and write down:
- Each wall: its width, and its height from the bottom of the siding to the soffit. Walls that are the same can share one row with “How many”.
- Each gable: the width at the base and the height from the base up to the peak.
- Windows and doors: width and height of each one. Use the quick buttons for common sizes.
- Corners: how many outside and inside corners the house has, for corner trim.
Don’t forget dormer cheeks, bay windows, chimney chases and the walls of attached garages. Add them as extra walls or gables.
The siding formulas
Net area = Σ(W × H) + Σ(½ × W × H gables) − Σ(openings)
Squares = net area × (1 + waste) ÷ 100 · Pieces = area ÷ (exposure ft × length ft)
The exposure (or reveal) is the part of each board you can see once it is installed. Lap siding overlaps the course below, so the exposure is smaller than the board width: an 8.25 in fiber cement plank shows 7 in.
Pieces per square by siding type
Use this to sanity-check a quote. Figures are for full-length pieces with no waste; check the manufacturer’s literature for your exact product.
| Siding | Exposure | Piece length | Pieces per square |
|---|---|---|---|
| Fiber cement lap, 8.25 in | 7 in | 12 ft | 14.3 |
| Fiber cement lap, 6.25 in | 5 in | 12 ft | 20 |
| Engineered wood lap, 8 in | ≈ 6.9 in | 16 ft | ≈ 10.9 |
| Vinyl, double 4.5 in | 9 in per panel | 12 ft 6 in | ≈ 10.7 |
| Vinyl, double 4 in | 8 in per panel | 12 ft 6 in | 12 |
| Wood bevel, 6 in | ≈ 4.5 in | 12 ft | ≈ 22 |
Whole-house example
A one-story house, 40 × 30 ft, with 9 ft walls, two gables at the 30 ft ends rising 7.5 ft, ten 3 × 5 ft windows and two 3 ft × 6 ft 9 in doors. These are the calculator’s starting numbers, so you can follow along.
- Walls: 2 × (40 × 9) + 2 × (30 × 9) = 1,260 sq ft.
- Gables: 2 × ½ × 30 × 7.5 = 225 sq ft.
- Openings: 10 × 15 + 2 × 20.25 = 190.5 sq ft.
- Net: 1,260 + 225 − 190.5 = 1,294.5 sq ft. With 10% waste: 1,424 sq ft = 14.24 squares.
- Pieces of 8.25 in fiber cement: 1,424 ÷ (7/12 × 12) = 204 planks. In 6.25 in planks it would be 285.
Trim and accessories
Siding is only half the order. The calculator estimates the trim from the same take-off:
- Corner trim: one run per corner, as tall as the wall.
- Window and door trim: the perimeter of every opening. In the example that is 199 lin ft before waste.
- Starter strip: along the bottom of every wall (140 lin ft in the example).
- Rake trim: up both slopes of each gable (67 lin ft in the example).
- Frieze or soffit trim along the top of the walls, plus flashing, house wrap, caulk and fasteners.
How much waste to allow
| House | Typical waste |
|---|---|
| Simple box, few openings | 10% |
| Average house with gables | 10–15% |
| Many corners, dormers, bays or angled walls | 15–20% |
Choosing a siding material
- Vinyl: lowest cost, light and fast to install, never needs paint. See the vinyl siding calculator for boxes and accessories.
- Fiber cement: heavy, durable and fire-resistant, usually painted. Cut with dust control.
- Engineered wood: lighter than fiber cement with long 16 ft pieces, so fewer joints.
- Wood: cedar bevel and clapboard look classic but need regular finishing.
- Board and batten: vertical look for farmhouse styles; use the board and batten calculator.
Measuring tricky areas
Real houses are rarely four rectangles. Here is how to handle the parts that trip people up:
- Dormers: the two triangular cheeks are gables (½ × depth × height each) and the front is a small wall. Add each one as its own row.
- Bay and bow windows: measure each face as a wall, then take off its window.
- Walls under a porch roof: measure from the porch floor to the porch ceiling, not to the main soffit.
- Chimney chases: add the three exposed faces as walls.
- Split levels and walk-outs: measure each section of wall to its own height. Uneven ground is easiest as an average height.
- Second stories: if you can’t reach, count siding courses on a photo and multiply by the exposure, or use the plans.
If you only have the house footprint, a rough estimate is the perimeter × wall height + gables, minus about 15% for openings. Use the full take-off before you order.
What drives siding cost
Enter your price per square or per piece to see the material cost. When comparing quotes, remember the other parts of the job:
| Item | How it is usually priced |
|---|---|
| Siding | Per square or per piece |
| Trim, corners, J-channel | Per piece or per linear foot |
| House wrap and flashing | Per roll |
| Tear-off and disposal of old siding | Per square |
| Installation labor | Per square, more for second stories and steep gables |
| Painting (fiber cement, wood) | Per square foot, unless pre-finished |
Common mistakes
- Using board width instead of exposure, which under-orders by 15% or more.
- Forgetting gables, especially on garages and dormers.
- Deducting every window and then running short on cut-heavy walls.
- Skipping trim, which can be a quarter of the material cost.
Notes for siding contractors
Openings rule. Many estimators only deduct openings over about 30–40 sq ft (garage and patio doors). Leave small windows out of the list if that is how you bid.
Gable math. Triangles waste more because every course is cut at an angle. Some pros add the full rectangle for gables instead of half.
Exposure tolerance. Changing exposure by ¼ in across a wall changes piece count by 3–5%. Use the manufacturer’s stated exposure.
WRB. House wrap goes on the gross wall area. Rolls are commonly 9 ft × 100 ft or 150 ft; plan laps of 6 in or more.
Tips
- Buy from one lot so colors match, and order everything at once.
- Keep a few spare pieces for future repairs.
- Check the roof pitch for gable heights with the roof pitch calculator: peak height = half the span × pitch ÷ 12.
- Send the list to your supplier with WhatsApp or Email under the result.
Frequently asked questions
How do I calculate how much siding I need?
Multiply each wall’s width by its height, add the gables (½ × base × height), subtract windows and doors, then add 10–15% for waste. Divide by 100 to get squares. A typical 40 × 30 ft one-story house with two gables needs about 1,295 sq ft net, or 14.2 squares with 10% waste.
What is a square of siding?
A square is 100 square feet of wall coverage. Siding, like roofing, is priced and sold by the square.
How many pieces of siding are in a square?
It depends on the exposure and length. For 8.25 in fiber cement lap with 7 in exposure in 12 ft planks, about 14.3 pieces cover a square. 6.25 in planks (5 in exposure) need 20 per square.
Should I subtract windows and doors?
Yes for big openings such as garage doors and patio doors. Many pros don’t subtract small windows, because the cut-offs are waste anyway. The calculator subtracts everything you list, so leave out openings you don’t want deducted.
How much waste should I add for siding?
About 10% for simple rectangular walls and 15% or more for houses with many gables, corners, dormers or angled cuts.
How do I measure a gable for siding?
Measure the width of the gable at its base and the height from the base to the peak. The area is half the width times the height. A 30 ft gable that rises 7.5 ft has 112.5 sq ft.
What trim do I need for siding?
Plan for corner trim at every outside and inside corner, trim or J-channel around windows and doors, a starter strip along the bottom, and trim along the gable rakes and under the soffits. The calculator estimates the linear feet.
Does this work for vinyl siding?
Yes, choose a vinyl profile, or use the vinyl siding calculator, which also counts boxes, J-channel, corner posts and starter strip in the lengths they are sold.