There and back
The formula uses twice the length you enter, because the current returns through the negative conductor.
Calculator
Voltage drop calculator for 12V and 24V
Enter current, length, cross-section and system voltage. You see what is left at the end of the cable, in volts and in percent.
- Free, no account needed
- 12V, 24V, 48V and 230V
- Result while you type
- Carries over into your diagram
System voltage
The result is guidance based on your input. Manufacturer instructions and local regulations always take precedence; you remain responsible for the installation.
Where the voltage goes
Every conductor has resistance. At high current over a long run you lose voltage that never reaches your load but heats the cable instead. At 12V that hurts: one volt of loss is over 8 % of your system voltage, so lights dim, an inverter alarms or a charger never fills the battery.
Size counts linearly
Twice as thick halves the loss. Doubling the length doubles the loss.
Limits per circuit
For charge currents and inverters 1 to 2 % is common, for lighting 3 %; the manufacturer decides.
From calculation to complete diagram
Designing a complete electrical system? In WireElectric the voltage drop is calculated for every connection in your diagram, including the links between battery, distributor and load.
You can start drawing without an account.
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Questions about voltage drop
- Which formula does this use?
- Loss is 2 × length × current × resistivity divided by the conductor size, using 0.0175 Ω·mm²/m for copper and 0.0282 for aluminium at 20 °C.
- Why does voltage drop matter so much at 12V?
- The loss in volts is the same for a given current and cable, but as a share of your system voltage it is nearly twenty times larger at 12V than at 230V.
- Should I calculate with a warm cable?
- Resistance rises with temperature, so the real loss is slightly higher. Keep margin for cables in an engine bay or roof duct.
- How do I see this in my own diagram?
- Fill in length and conductor size per connection in the editor; the check then works through every connection in your system at once.
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