Cable Cross-Section Calculator
Minimum conductor cross-section needed to keep voltage drop within a chosen limit.
Results
Conductor cross-section
3.551
mm²
Conductor cross-section
3.075
mm²
Voltage drop
6.90
V
What this tool does
This reverses the voltage drop calculation: you set the drop you are willing to accept and it returns the copper cross-section that achieves it. It covers the voltage-drop criterion only — current-carrying capacity, installation method, grouping and protection must be checked separately against your national wiring rules.
Formula
S = 2 × ρ × L × I ÷ ΔU
Variables
| Symbol | Meaning | Unit |
|---|---|---|
i | Current | A |
l | One-way cable length | m |
u | Voltage | V |
dp | Voltage drop | % |
ro | Resistivity | Ω·mm²/m |
S1 | Conductor cross-section | mm² |
S3 | Conductor cross-section | mm² |
dU | Voltage drop | V |
Worked example
- Current20 A
- One-way cable length35 m
- Voltage230 V
- Voltage drop3 %
- Resistivity0.0175 Ω·mm²/m
- Conductor cross-section3.551 mm²
- Conductor cross-section3.075 mm²
- Voltage drop6.90 V
Limitations
- Electrical installations are governed by national wiring rules. Cable sizing also depends on installation method, grouping, ambient temperature and protection devices, which this calculator does not evaluate.
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.