What is the Voltage Drop Calculator?
The voltage drop calculator is a free online tool that helps you work out voltage drop quickly and accurately. It uses the standard formula Vdrop = 2 x I x (resistivity x length / area) 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 current and cable length.
- Enter conductor resistivity and area.
- See the voltage drop.
Formula used
Vdrop = 2 x I x (resistivity x length / area)Explanation of each input
- Current (A) โ the current used in the calculation.
- Cable length (one way) (m) โ the cable length (one way) used in the calculation.
- Resistivity (ohm mm2/m) โ the resistivity (ohm mm2/m) used in the calculation.
- Conductor area (mm2) โ the conductor area used in the calculation.
- Supply voltage (V) โ the supply voltage used in the calculation.
Understanding your result
- Voltage drop โ the calculated voltage drop in V.
- Drop โ the calculated drop in %.
Step-by-step calculation
For the example values 10A, 30m, 2.5mm2 Cu:
- Apply the formula:
Vdrop = 2 x I x (resistivity x length / area) - Substitute the values: 2x10x(0.0175x30/2.5)
- Result: about 4.2 V
Worked example
| Inputs | 10A, 30m, 2.5mm2 Cu |
|---|---|
| Working | 2x10x(0.0175x30/2.5) |
| Result | about 4.2 V |
Benefits and practical uses
This calculator saves you time and reduces errors when you need voltage drop. 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 resistivity by default; single-phase two-wire.
Frequently asked questions
What voltage drop is acceptable?
Many codes recommend keeping total drop under 3-5% of supply voltage.
Disclaimer: Results are provided for general information. Please verify important figures independently.