Siding Calculator
Net wall area to squares, boards and trim.
With the default inputs: Net wall area 1200 ft² · Exposure per board 7 in · Board length 12 ft etc.Siding squares 13.2 sq
Use your own dimensions ↓Inputs
Result
| Area with waste | 1320ft² |
| Coverage per board | 7.00ft² |
| Boards | 189boards |
| Total board length | 2,268ft |
| Trim (est.) | 55ft |
| Furring at 16 in o.c. | 83ft |
How this is worked out
One square is 100 ft², the same unit roofing uses. Boards = area with waste ÷ coverage per board, where coverage is board length x exposure ÷ 12. Exposure is the trap: the nominal width of lap siding is not the exposure - a nominal 8 in board exposes only 7 in because the course above laps over it by an inch. Calculating on nominal width under-orders by about 14%, which is the most common siding estimate error. Deduct openings from the net area: one 3 x 5 ft window is 15 ft², or about 1.5 boards. Trim is roughly 40% of perimeter as a guide; count corners and openings on the elevations for the real figure.
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Enter a target result; the other inputs stay fixed and this one is worked out.
Formula
| 1 square = 100 ft² | same as roofing |
| Coverage = length × exposure/12 | exposure, not nominal width |
| Boards = area × (1+waste) ÷ coverage | round up |
| Squares = area × (1+waste) ÷ 100 |
How to work it out
- Work out net wall area: perimeter x average height, less openings (about 15 ft² per window, 20 per door).
- Use exposure to get coverage per board, not nominal width - nominal 8 in exposes 7 in.
- Boards = area x (1 + waste) ÷ (length x exposure/12).
- Squares = area ÷ 100, which is what the supplier works in.
- Waste: 10% simple elevation, 15% with many openings and corners, 20% on busy elevations with gables.
Where it goes wrong
- Calculating on nominal width - that under-orders by 14-20%, you run short mid-job, and the top-up lot will not match.
- Not deducting openings - one window is 15 ft², and a whole house is two or three squares out.
- Nailing tight with no play - boards move thermally and buckle; the most common siding deformation.
Material and cost
Vinyl siding is about USD 3-6 per ft² in material, fibre cement 4-8 and composite 5-9. Installation labour runs USD 4-8 per ft². A full exterior re-clad including strip, furring, boards and trim commonly lands at 9-16 per ft², so 1200 ft² of wall is roughly 11000-19000.
On site
- Get the house wrap on first and lapped correctly (upper over lower). That is the real weather barrier, not the siding.
- Leave 1/8 in under every board so water can escape rather than sitting on the course below.
- Keep 6 in clear of grade and 1 in clear of roofs - a hard requirement against wicking, especially for fibre cement.
Basis
- ASTM C1186 Standard Specification for Flat Fiber-Cement Sheets
- IRC International Residential Code, Chapter R703 (exterior covering)
- ASTM E330 Standard Test Method for Structural Performance of Exterior Windows, Doors, Skylights and Curtain Walls by Uniform Static Air Pressure Difference
FAQ
What is the difference between exposure and nominal width?
Can I go over the old siding?
What about nailing and gaps?
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Siding Calculator. 2026-10-25. https://jianzhujisuan.com/en/siding-squares