Cable Section Calculator
Estimate the minimum cable cross-sectional area (mm²) based on voltage drop limits, conductor material, length, and load. This is a planning tool for quick checks.
Why a cable section calculator matters
Choosing cable size is not just about whether the wire “works.” It affects safety, efficiency, voltage quality at the load, and long-term operating cost. A cable that is too small may overheat, suffer higher losses, and produce poor equipment performance due to excessive voltage drop. A cable that is oversized may be unnecessarily expensive.
This cable section calculator helps you estimate the required conductor area quickly using voltage-drop based sizing logic. It is especially useful at the early design stage for feeders, branch circuits, pumps, EV charging runs, workshop circuits, and off-grid systems.
What this calculator uses
Primary inputs
- System type: DC, single-phase AC, or three-phase AC.
- Material: Copper or aluminum (different resistivity values).
- Voltage and load: Enter current directly, or enter kW and let the calculator estimate current.
- Length: One-way cable route length in meters.
- Allowed voltage drop: Typical design targets are 2–5% depending on local code and circuit type.
- Conductor temperature: Higher temperature means higher resistance.
- Design margin: Adds practical headroom and rounds up to the next standard size.
Calculation method
The calculator estimates conductor area with a resistance-based voltage drop approach:
- DC and single-phase: A = (2 × ρ × L × I) / ΔV
- Three-phase: A = (√3 × ρ × L × I) / ΔV
Where ρ is resistivity in Ω·mm²/m corrected for temperature, L is one-way length in meters, I is current in amperes, and ΔV is allowed voltage drop in volts.
Quick interpretation guide
After calculating, you’ll see:
- Design current used in the math.
- Allowed voltage drop in volts and percent.
- Minimum theoretical section.
- Section with design margin.
- Recommended next standard cable size.
- Estimated actual voltage drop with selected standard size.
In real projects, confirm with your local electrical standard (IEC, NEC, BS, etc.), especially for ampacity, installation method, grouping, insulation type, ambient temperature, and protective device coordination.
Common standard conductor sizes (mm²)
| Small circuits | General distribution | Heavy feeders |
|---|---|---|
| 1.5, 2.5, 4, 6 | 10, 16, 25, 35, 50, 70 | 95, 120, 150, 185, 240, 300+ |
Practical tips before finalizing cable size
1) Verify ampacity separately
Voltage drop alone does not guarantee thermal safety. A cable may meet drop limits but still fail ampacity requirements due to installation conditions.
2) Consider future load growth
Adding 15–25% design margin is common for practical engineering decisions, especially where expansion is expected.
3) Watch long runs carefully
Long cable routes often become voltage-drop limited. In these cases, the chosen section may be much larger than what current alone suggests.
4) Aluminum vs copper
Aluminum can reduce cost and weight but typically needs larger cross-section than copper for the same voltage drop target.
FAQ
Is this calculator suitable for both residential and industrial projects?
It is suitable for preliminary sizing in both settings. Final design should always be validated against applicable code requirements and manufacturer data.
Why does temperature matter?
As conductor temperature rises, resistance increases, resulting in greater voltage drop for the same load current.
Can I use this for motor circuits?
Yes for a first estimate, but motor starting current, duty cycle, and permissible starting voltage dip must be checked separately.
Does this include earth/ground conductor sizing?
No. Protective conductor sizing follows different rules and must be checked independently.
Disclaimer: This calculator provides engineering estimates, not certified design output. Always verify against local regulations and have final selections reviewed by a qualified electrician or electrical engineer.