# Siding Calculator

Net wall area to squares, boards and trim.

- Page: https://jianzhujisuan.com/en/siding-squares
- Category: Finishes (https://jianzhujisuan.com/en/c/finishes)
- Chinese version: https://jianzhujisuan.com/zh/siding-squares.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Net wall area 1200 ft², Exposure per board 7 in, Board length 12 ft, Waste Simple elevation (+10%)): **Siding squares 13.2 sq**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Net wall area | number | 1200 | ft² |  |
| Exposure per board | number | 7 | in |  |
| Board length | number | 12 | ft |  |
| Waste | select | Simple elevation (+10%) | — |  |

## 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**: 

## Worked example

1200 ft² of wall at 7 in exposure, 12 ft boards and 10% waste: 1320 ft² = 13.2 squares, 7 ft² per board, so 189 boards (2268 linear feet).

## Questions

### What is the difference between exposure and nominal width?

Each lap siding course is covered by the one above, and only the exposed part counts. Common pairs: nominal 6 in exposes 5 in, nominal 8 in exposes 7 in, and nominal 10 in exposes 8-9 in. Always calculate on exposure - using nominal width under-orders by 14-20%. The coverage figure printed on the bundle is the safest source.

### Can I go over the old siding?

Yes, provided the sheathing can carry it, the old boards are sound and you add furring to bring it flat. It saves tear-off and disposal, but the wall moves out, so windows and doors need deeper trim and the detail work can cost more than stripping. Fibre cement is much heavier than vinyl - check the structure before layering it on.

### What about nailing and gaps?

Nail on the centreline at the manufacturer's spacing, commonly 16 in, and leave about 1/32 in of play so the board can move thermally - nailed tight it buckles. Butt joints need a 1/8 in gap and corners want trim rather than a tight butt. Fibre cement also needs 6 in clear of grade and 1 in clear of a roof to stop it wicking moisture.

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