Siding Calculator
Estimate the wall area and number of siding squares you need from your wall perimeter, height, door and window openings, and a waste allowance. Works for vinyl, fiber cement and lap siding.
Updated 2026-06-09 · Free · No sign-up · Runs privately in your browser
What is a siding calculator?
A siding calculator estimates how much exterior siding you need by turning your wall measurements into net wall area and then into siding squares — the 100-square-foot unit that vinyl, fiber cement and lap siding are all sold and priced in. Instead of guessing at boxes, you enter the wall perimeter, height, and the area of doors and windows, and the tool returns the exact coverage to order plus a waste cushion for cuts and offcuts.
It is a planning and budgeting estimate. Final quantities should always be confirmed against the manufacturer’s coverage per box and a contractor’s on-site take-off.
How is siding quantity calculated?
The siding area is the wall surface minus the openings, scaled up by a waste factor and divided into squares. The calculator uses this exact method:
- Gross wall area = perimeter × height
- Net wall area = gross − doors and windows area (never below zero)
- Area with waste = net × (1 + waste% ÷ 100)
- Siding squares = area with waste ÷ 100
A square equals 100 sq ft, so dividing by 100 converts square feet directly into the unit on the price sheet. The net and waste areas are shown rounded to the nearest square foot; squares are shown to two decimals so you can round up to whole boxes yourself.
Worked examples you can reproduce
These match the calculator’s output exactly.
Example 1 — single-story ranch (default values). Perimeter 140 ft, height 9 ft, openings 120 sq ft, waste 10%.
- Gross = 140 × 9 = 1,260 sq ft
- Net = 1,260 − 120 = 1,140 sq ft
- With waste = 1,140 × 1.10 = 1,254 sq ft
- Squares = 1,254 ÷ 100 = 12.54 squares
Example 2 — taller two-section home. Perimeter 120 ft, height 10 ft, openings 180 sq ft, waste 10%.
- Gross = 120 × 10 = 1,200 sq ft
- Net = 1,200 − 180 = 1,020 sq ft
- With waste = 1,020 × 1.10 = 1,122 sq ft
- Squares = 1,122 ÷ 100 = 11.22 squares
In both cases you would round up — to 13 and 12 squares respectively, or to whole boxes based on each box’s coverage.
How much siding for common house sizes?
The table below shows rough estimates using a 9 ft wall height, typical openings, and 10% waste. Your perimeter and openings will differ, so use the calculator for your own numbers.
| Wall perimeter | Wall height | Openings | Net area | With 10% waste | Squares |
|---|---|---|---|---|---|
| 100 ft | 9 ft | 100 sq ft | 800 sq ft | 880 sq ft | 8.80 |
| 140 ft | 9 ft | 120 sq ft | 1,140 sq ft | 1,254 sq ft | 12.54 |
| 160 ft | 9 ft | 150 sq ft | 1,290 sq ft | 1,419 sq ft | 14.19 |
| 180 ft | 18 ft (2 story) | 250 sq ft | 2,990 sq ft | 3,289 sq ft | 32.89 |
Which siding type are you estimating?
The area math is the same for every product sold by the square; only waste and price change. This guide helps you set realistic inputs.
| Siding type | Typical waste | Notes |
|---|---|---|
| Vinyl | 8-12% | Lightweight, sold in boxes that usually cover 2 squares; most forgiving for DIY. |
| Fiber cement (lap) | 10-15% | Heavier and brittle (e.g. Hardie board); plan extra for breakage and dust control. |
| Wood / engineered lap | 12-15% | More cuts and overlap; diagonal or staggered patterns waste more. |
| Board and batten | 10-15% | Vertical panels plus battens; measure battens separately. |
Real-world use cases
- Budgeting a re-side: multiply squares by price per square to estimate material cost before calling contractors.
- DIY ordering: convert squares to boxes using the coverage on the label, then add a spare box for future repairs.
- Comparing quotes: check a contractor’s material count against your own take-off to spot padding or under-ordering.
- Insurance and resale prep: document wall area for claims or listing details.
Tips and common mistakes
- Don’t confuse floor area with wall area. A “2,000 sq ft house” refers to floor space; siding covers the vertical walls, which is a different number.
- Include gable triangles. For a gable end, area ≈ ½ × base × height. Add gables into your perimeter-times-height total or as extra openings adjustment.
- Measure openings generously. Use the full rough opening (width × height) for each door and window, then sum them.
- Round up, never down. Dye-lot and color matching make it hard to buy one matching box later, so order a little extra in the same batch.
- Account for accessories separately. J-channel, corner posts, starter strip and soffit are not part of the field-siding square count.
For related exterior projects, see our fence calculator or browse more construction calculators.
Limitations and accuracy notes
This tool assumes uniform wall height and treats the building as a simple shape, so steep gables, turrets, wraparound porches and multi-pitch walls need to be added manually. It does not account for siding-specific course math, overlap loss on lap profiles beyond the waste factor, or trim and accessory pieces. A 10% waste figure is a planning default, not a guarantee — complex elevations routinely run 12-15%.
Disclaimer: This is an estimating aid for planning and budgeting only, not a substitute for a professional on-site measurement. Always confirm quantities against the manufacturer’s stated coverage per box and a qualified installer’s take-off before purchasing.
Frequently asked questions
How much siding do I need?+
Multiply the wall perimeter by the wall height for gross area, subtract door and window openings, add a waste allowance, then divide by 100 to get siding squares. For a 140 ft perimeter, 9 ft walls and 120 sq ft of openings at 10% waste, that is 12.54 squares.
What is a siding square?+
A square is the standard unit siding is sold and quoted in: it covers exactly 100 square feet of wall. So 1,254 sq ft of siding area (after waste) equals 12.54 squares.
How much waste should I add for siding?+
About 10% for simple, boxy walls. Add 12-15% for many corners, gables, dormers, or diagonal lap siding cuts, where offcuts pile up faster.
How do I measure wall perimeter for siding?+
Measure the length of each exterior wall at ground level and add them together. For an L-shaped or multi-section home, sum every wall segment, including the recesses.
Do I subtract doors and windows from siding area?+
Yes. Add up the area of every door and window opening (width times height in feet) and subtract that total from the gross wall area before applying waste.
How many squares of siding cover a 2,000 sq ft house?+
Wall area is not the same as floor area. A two-story 2,000 sq ft home typically has roughly 1,800-2,200 sq ft of wall, or about 18-22 squares after openings and waste.
Does this calculator work for vinyl, fiber cement and lap siding?+
Yes. The area math is identical for vinyl, fiber cement (such as Hardie board) and wood or engineered lap siding, since all are sold by the square. Only the waste factor and price per square change.
How do I convert squares to boxes of siding?+
Check the coverage printed on the box: most vinyl siding boxes cover 2 squares (200 sq ft). Divide your total squares by the box coverage and round up to whole boxes.