When designing a vehicle’s electrical system, the correct AWG to mm² conversion saves time and prevents mistakes. This page brings together automotive wire sizes, battery cable recommendations, 12V wire sizing rules, and voltage drop formulas with practical examples.
AWG to mm² Conversion Table
| AWG | mm² | Recommended continuous (A) | Maximum short‑term (A) | Application (motorsport) |
|---|---|---|---|---|
| 18 | 0.82 | 9 | 16 | Sensors, dashboards, CAN bus, small control signals |
| 16 | 1.3 | 13 | 22 | Engine harness, sensors, data loggers, auxiliary lights |
| 12 | 3.3 | 23 | 41 | Fuel pumps, ECUs, cooling fans |
| 8 | 8.4 | 46 | 73 | Electric water pumps, large fans, auxiliary battery feeds |
| 4 | 21 | 85 | 135 | Main switch → fuse box, auxiliary battery links, winches |
| 1/0 | 53 | 150 | 245 | Main battery cable to starter motor, high‑current inverters |
Formulas for Voltage Drop
Power: P = V × I. Example: 12 V × 30 A = 360 W.
Resistance: R = ρ × (L / A), where ρ ≈ 0.0175 Ω·mm²/m for copper, L = total length (out + return), A = cross‑section in mm².
Voltage drop: ΔV = I × R. As a percentage: (ΔV / V) × 100 %.
Power loss: Ploss = I² × R.
Practical Example
Target: maximum 3 % drop in a 12 V system (0.36 V). Load 25 A, distance 5 m → total length 10 m.
- 16 AWG (1.3 mm²): ΔV ≈ 3.3 V → far too high.
- 8 AWG (8.4 mm²): ΔV ≈ 0.5 V (~4.3 %) → better, but still too high for critical loads.
- Conclusion: choose a thicker cable (e.g. 6 AWG), size primarily by voltage drop.
Quick Guidelines for Automotive Wiring
- Keep voltage drop ≤ 3 % for critical loads in 12 V systems.
- Engine bay heat and bundled wires require derating – use a thicker battery cable than the table alone suggests.
- Select insulation by location: XLPE or Teflon 105–125 °C for engine bay, PVC 85–90 °C for interior runs.
- Document each run: AWG ↔ mm², length, fuse, and target %ΔV. This simplifies troubleshooting and service.
- Always use quality terminals and provide mechanical protection – especially for the main battery cable and high‑current feeds.
Summary
When planning a vehicle’s electrical system, the AWG to mm² conversion table is a practical tool that connects American and European wire sizes. The correct automotive wire choice depends not only on ampacity but also on voltage drop. In practice this means that a battery cable should always be sized with some margin, so that a 12V system remains reliable under load. By considering cross‑section, length and operating conditions, you avoid unnecessary losses and ensure that power is delivered efficiently and safely.