Calculator KB-46
Wire voltage drop calculator
Especially important in low-voltage circuits: at 12 V, a one-volt drop is already significant.
Result
In brief: Calculate cable voltage drop based on length, current and cross-sectional area for copper and aluminum: voltage and percentage loss, voltage at the load, and power loss. Example: Voltage drop: 1.4 V.
Calculation example
| Cable length | 10 м |
|---|---|
| Current | 10 A |
| Wire gauge | 2.5 mm² |
| Source voltage | 12 V |
| Material | Copper |
| Wires in the circuit | Two, out and back |
| Voltage drop | 1.4 V |
|---|---|
| As a percentage | 11.7 % |
| Voltage across the load | 10.6 V |
| Line resistance | 140 mΩ |
| Power loss | 14 W |
How it is calculated
ΔU = I · R
P = I · ΔU
Current flows both ways, so the line length is counted twice. Resistance increases with length and decreases with cross-sectional area. The resistivity of copper is 0.0175, and aluminum 0.0283 Ω·mm²/m.
What to look for
- In low-voltage systems, try to keep losses within 3–5%.
- If losses are high, increase the system voltage: at the same power, current drops, and losses drop with the square of the current.
Frequently asked questions
How do you calculate voltage drop in a cable?
ΔU = I · ρ · 2L / S. For 10 m of cable carrying 10 A, with a 2.5 mm² copper conductor, the drop is 1.4 V, or 11.7% at 12 V.
What voltage drop is acceptable?
For low-voltage circuits, 3–5% is a common guideline; for sensitive electronics, keep it lower. This matters most at 12 V and below.
How do you reduce cable losses?
Use a larger cross-section, shorten the cable, or increase the voltage. Going from 12 to 24 V at the same power halves the current and cuts wire losses by a factor of four.
