Calculator KB-08
Wire Gauge Calculator
Choose a cable cross-section for a battery, inverter, or power supply based on current and allowable voltage drop.
Result
| Wire gauge | Voltage drop | Losses |
|---|
In brief: Calculate wire gauge based on current and allowable voltage drop for copper and aluminum: standard size, losses, diameter, and AWG. Example: Recommended wire gauge: 6 mm².
Calculation example
| Current | 20 A |
|---|---|
| Voltage | 12 V |
| Allowable voltage drop | 3 % |
| Cable length one way | 3 м |
| Material | Copper |
| Installation | Open air |
| Recommended wire gauge | 6 mm² |
|---|---|
| Minimum based on voltage drop | 5.83 mm² |
| Minimum based on current | 1.5 mm² (23 A) |
| Voltage drop at this gauge | 0.35 V (2.9 %) |
| Cable losses | 7 W |
| Conductor diameter | 2.76 mm |
| Approx. AWG | 9 |
How it is calculated
The wire gauge is selected based on two criteria, using whichever requires the larger size: the wire must not overheat (PUE tables 1.3.4 and 1.3.5) and must not lose too much voltage. Resistivity is taken as 0.0175 for copper and 0.0283 Ω·mm²/m for aluminum.
What to look for
- In low-voltage circuits, voltage drop is almost always the deciding factor: a 0.5 V drop on 12 V is noticeable, while on 230 V it can be ignored.
- Cheap wires may have a smaller actual cross-section than specified, and many use copper-clad aluminum conductors. If in doubt, go one size up.
- This calculator helps estimate cable sizes for batteries, inverters, and power supplies. Fixed 230 V wiring must be designed to current standards, taking circuit breakers and installation method into account.
Frequently asked questions
What wire gauge do I need for 20 A at 12 V?
For a 3 m one-way run and a 3% voltage drop, you need 5.83 mm², or the standard 6 mm². Based on heating alone, 1.5 mm² would be enough: in low-voltage circuits, voltage drop is the deciding factor.
Why is cable length counted twice?
Current flows to the load and back, so calculate the line resistance using twice the cable length: 3 m of cable means 6 m of wire.
How does aluminum differ from copper in calculations?
Its resistivity is about 1.6 times higher: 0.0283 versus 0.0175 Ω·mm²/m. So use a larger cross-section for aluminum wire, and pay special attention to the connections.
