Cable Size & Thickness Calculator
Use this tool to estimate the required cable cross-sectional area (mm²) and equivalent conductor thickness for copper or aluminum conductors.
Default: Copper 6 A/mm², Aluminum 4 A/mm²
What this calculator does
Electrical cable thickness is usually expressed as cross-sectional area in mm², not insulation diameter. Choosing the right cable size helps prevent overheating, excessive voltage drop, and energy waste. This calculator estimates a practical cable size by checking two core limits:
- Ampacity limit: the cable must carry current safely.
- Voltage drop limit: the cable must keep voltage loss within your target percentage.
The result shows the larger of these two requirements, then rounds up to a common standard cable size.
How the calculation works
1) Design current
Real-world installations usually include margin. We apply:
Design Current = Load Current × Safety Factor
2) Area from voltage drop
For copper/aluminum conductors using resistive drop approximation:
- Single-phase / DC: A = (2 × I × ρ × L) / ΔV
- Three-phase: A = (√3 × I × ρ × L) / ΔV
Where:
- A = conductor area (mm²)
- I = design current (A)
- ρ = resistivity (Copper ≈ 0.0175, Aluminum ≈ 0.0282 Ω·mm²/m)
- L = one-way cable length (m)
- ΔV = allowed voltage drop in volts
3) Area from current density
A simple thermal estimate:
A = I / J
Where J is current density in A/mm². Typical planning values are 6 A/mm² for copper and 4 A/mm² for aluminum.
4) Recommended size
The calculator selects:
Required Area = max(Area from voltage drop, Area from ampacity)
Then it rounds up to the next standard cable size (1.5, 2.5, 4, 6, 10, 16, 25 mm², etc.).
Quick reference: common low-voltage cable sizes
| Nominal Area (mm²) | Typical Use Case | Approx. Solid Conductor Diameter |
|---|---|---|
| 1.5 | Lighting circuits | 1.38 mm |
| 2.5 | Socket circuits (light loads) | 1.78 mm |
| 4 | Heavier socket/radial loads | 2.26 mm |
| 6 | Small submain / cookers | 2.76 mm |
| 10 | EV chargers / submains | 3.57 mm |
| 16+ | Larger feeders and distribution | 4.51 mm and above |
Important design factors not fully modeled
This calculator is designed for fast estimating. Final cable sizing should also account for:
- Installation method (in conduit, buried, tray, free air)
- Ambient temperature and grouping derating
- Insulation type and conductor temperature rating
- Harmonics and nonlinear loads
- Short-circuit withstand and fault loop impedance
- Local code requirements (NEC, IEC, BS 7671, etc.)
Example scenario
Suppose you have a 32 A single-phase load, 25 m one-way run, 230 V supply, 3% voltage drop limit, copper conductor, and safety factor 1.25. The tool calculates design current, checks voltage drop and thermal area, and recommends the next standard size above the controlling result.
In many practical cases, voltage drop controls long runs, while ampacity controls short but high-current runs.
Final note
Use this page as a planning tool for electrical cable thickness calculation. Always verify with the applicable electrical code and a licensed electrician or electrical engineer before installation.