Loft boarding calculator: boards, packs and loft legs
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check your supplier's or maker's figures before ordering.
Short answer
Worked example
| You enter | Value |
|---|---|
| Length to board, along the joists | 5 m |
| Width to board, across the joists | 2 m |
| Board length | 1,220 mm |
| Board width | 320 mm |
| Waste allowance | 10% |
| Joist centres | 400 mm |
You need 29 loft boards and 96 loft legs
| Result | Value |
|---|---|
| Boards | 29 |
| Loft legs (one per board row per joist) | 96 |
| Area boarded | 10 m² |
Show the working
- Area: 5 × 2 m = 10 m²
- Boards: 10 m² × 1.1 (10% waste) ÷ (1,220 × 320 mm = 0.39 m²) = 28.18, rounded up to 29
- Joist lines: 2 m ÷ 400 mm, rounded up, + 1 = 6; board rows: 5 m ÷ 320 mm, rounded up = 16
- Legs: 6 × 16 = 96
How it works
- Boards = length × width × (1 + waste) ÷ (board length × board width), rounded up; packs = boards ÷ boards per pack, rounded up
- Boards run across the joists, so each row of boards (one board width) crosses every joist once
- Joist lines = width across the joists ÷ joist centres, rounded up, + 1; board rows = length along the joists ÷ board width, rounded up
- Legs = joist lines × board rows (one leg at each crossing); screws = legs × screws per leg + boards × screws per board
Squashing loft insulation reduces how well it works, so the legs should lift the boards clear of it.
Ceiling joists aren't always designed to carry storage loads: if in doubt, ask a builder or structural engineer.
Our default (adjustable)
These are typical planning figures and our own allowances, not facts about your product. Change any of them in the calculator to match your bag, pack or tin.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Board length | 1.22 m | Common UK size Not yet checked against the source | From your product brief v2 LB1 (1.22 × 0.32 m boards). Researcher to confirm against merchant listings. |
| Board width | 0.32 m | Common UK size Not yet checked against the source | From your product brief v2 LB1 (1.22 × 0.32 m boards). Researcher to confirm against merchant listings. |
| Waste allowance | 10 % | Our assumption Not yet checked against the source | Our choice: change it to suit your job brief v2 LB1 (10%). |
| Boards per pack | Enter from the bag, pack or tin | Common UK size Not yet checked against the source | From your product From the pack. |
| Screws per leg | Enter from the bag, pack or tin | Typical value Not yet checked against the source | From your product From the leg maker's fixing instructions. |
| Screws per board | Enter from the bag, pack or tin | Typical value Not yet checked against the source | From your product From the board or leg maker's fixing instructions. |
Regulations and standards
- Energy Saving Trust and loft-leg makers: don't compress loft insulation
Our checks use the guidance for England unless a badge says otherwise. Wales, Scotland and Northern Ireland have their own rules: check the source for where you live.