What is the Cable Size Calculator?
The cable size calculator is a free online tool that helps you work out cable size quickly and accurately. It uses the standard formula Pick the smallest copper cross-section keeping voltage drop within about 3% (simplified) and shows the result instantly as you type, along with a full breakdown so you can see exactly how the answer was reached.
How to use this calculator
- Enter the load current.
- Enter the cable run length.
- See a suggested cable size.
Formula used
Pick the smallest copper cross-section keeping voltage drop within about 3% (simplified)Explanation of each input
- Load current (A) โ the load current used in the calculation.
- Cable length (m) โ the cable length used in the calculation.
- Voltage (V) โ the voltage used in the calculation.
Understanding your result
- Suggested copper size โ the calculated suggested copper size in mm2.
- Estimated drop โ the calculated estimated drop in %.
Step-by-step calculation
For the example values 20A, 30m, 230V:
- Apply the formula:
Pick the smallest copper cross-section keeping voltage drop within about 3% (simplified) - Substitute the values: drop-based sizing
- Result: about 4 mm2
Worked example
| Inputs | 20A, 30m, 230V |
|---|---|
| Working | drop-based sizing |
| Result | about 4 mm2 |
Benefits and practical uses
This calculator saves you time and reduces errors when you need cable size. It is useful for students, professionals and anyone who wants a fast, reliable answer without manual calculation. Results update instantly, work in your browser and can be copied or shared in one click.
Assumptions and limitations
- Copper conductor; about 3% target drop; simplified - not a code calculation.
Frequently asked questions
Is this a substitute for an electrician?
No. This is a rough guide; always follow local wiring regulations and consult a licensed electrician.