Voltage Drop Calculator
Calculate voltage drop across cables and wires for copper and aluminum conductors.
Component Values
Results
AWG Wire Size Reference
| AWG | mm² | Copper (Ω/km) | Aluminum (Ω/km) |
|---|---|---|---|
| 10 | 5.261 | 3.19 | 5.04 |
| 12 | 3.309 | 5.08 | 8.01 |
| 14 | 2.081 | 8.07 | 12.73 |
| 16 | 1.309 | 12.83 | 20.24 |
| 18 | 0.823 | 20.41 | 32.20 |
| 20 | 0.518 | 32.43 | 51.16 |
| 22 | 0.326 | 51.53 | 81.29 |
| 24 | 0.205 | 81.95 | 129.27 |
| 26 | 0.129 | 130.23 | 205.43 |
| 28 | 0.081 | 207.41 | 327.16 |
| 30 | 0.0509 | 330.06 | 520.63 |
Understanding voltage drop in cables
Voltage drop is the reduction in voltage across a conductor due to its resistance. Every wire has resistance proportional to its length and inversely proportional to its cross-sectional area. The total cable resistance for a round-trip circuit is R = p x 2L / A, where p is the material resistivity, L is the one-way length, and A is the cross-section.
The IEC 60364 standard recommends that voltage drop should not exceed 3% for lighting circuits and 5% for other loads. The NEC similarly recommends 3% for branch circuits and 5% total. Excessive voltage drop wastes energy as heat in the cable and can cause equipment to malfunction, especially motors and sensitive electronics.
Copper (p = 1.68e-8 ohm.m) is the most common conductor material due to its low resistivity. Aluminum (p = 2.65e-8 ohm.m) has about 60% higher resistivity but is lighter and cheaper, making it popular for overhead power lines and large installations. To compensate, aluminum cables use a larger cross-section than copper for the same current capacity.
For long cable runs -- solar panel arrays, industrial plants, EV charging stations -- voltage drop calculation is critical. Increasing wire gauge (larger cross-section) reduces resistance and voltage drop. The trade-off is cost and weight. Always verify that your cable sizing satisfies both current capacity (ampacity) and voltage drop requirements.
Cable Resistance
R_cable = ρ × 2L / AVoltage Drop
V_drop = I × R_cableDrop Percentage
Drop% = (V_drop / V_source) × 100Key Points
- Voltage drop is proportional to current and cable length
- IEC 60364: max 3% for lighting, 5% for other circuits
- Copper has ~40% less resistivity than aluminum
- Doubling the cross-section halves the voltage drop
- Round-trip length = 2 x one-way cable length
Applications
- Residential and commercial wiring design
- Solar panel array cable sizing
- EV charging station installation
- Industrial plant power distribution