12 Volt & Plywood
Numbers you can
actually cut to
Reference material for wiring and cabinetry in vans, RVs, boats and off‑grid spaces. Everything in both unit systems, and where the two systems describe genuinely different products, we say so instead of converting.
Tools
The two-unit problem
Most sites that publish build numbers pick one unit system and convert. That works for a length and fails badly for a material, because a sheet of plywood and a length of cable are sold to different standards in different countries. These are not the same object with two labels.
| Sheet | Metric | Imperial | Where |
|---|---|---|---|
| us-4x8 | 1220 × 2440 mm | 4 ft × 8 ft | US, CA, UK |
| eu-2500x1250 | 1250 × 2500 mm | metric only | EU |
| au-2400x1200 | 1200 × 2400 mm | metric only | AU, NZ |
| baltic-birch-5x5 | 1525 × 1525 mm | 5 ft × 5 ft | US, CA, UK, EU, AU |
The European sheet is 60 mm longer and 30 mm wider than the British one. Baltic birch is square. A cut list nested for a 4 × 8 sheet can be physically unbuildable on Australian stock, because the long side is 40 mm short.
| Called | Actually | Never swap with |
|---|---|---|
| 3/4 in | 18.26 mm | 18 mm |
| 18 mm | 18 mm | 3/4 in |
| 1/2 in | 11.91 mm | 12 mm |
| 12 mm | 12 mm | 1/2 in |
| 3/8 in | 9.13 mm | 9 mm |
| 9 mm | 9 mm | 3/8 in |
| 15 mm | 15 mm | — |
A US sheet sold as three quarters of an inch measures 18.26 mm. A metric 18 mm sheet measures 18 mm. Cut a groove for one and fit the other, and the joint rattles.