What is it?
The Voltage Drop Calculator shows how much voltage is lost along a cable. It shows the drop in volts and as a percent, the voltage at the far end, and the power wasted in the cable.
Who is it for?
Electricians, solar installers, borewell pump owners and engineers planning long cable runs.
How to use it
Choose the Supply (Single-phase AC or DC (2 wires) or Three-phase AC) and Wire metal (Copper or Aluminium). Enter the Supply voltage, Current, Cable length (one way) and Wire size in mm². The answer appears as you type; there is no Calculate button. Tap Copy result to copy it, or Share on WhatsApp to send it.
How it is worked out
Drop = factor × resistivity × length × current ÷ wire size (copper 0.0172, aluminium 0.0282 Ω·mm²/m at 20 °C). Factor is 2 for single phase, √3 for three phase. Enter the one-way length; the calculator accounts for the return path.
How much drop is acceptable?
- A common rule is no more than 3% for lighting and 5% for other loads from the meter to the furthest point. Your local wiring code sets the exact limit.
- Too much drop makes motors and pumps run hot, lights dim and inverters cut out.
Fixing a high drop
Use a thicker cable (the Wire Size Calculator finds the smallest that works), shorten the run, or use a higher voltage. Hot cables have more resistance, so long runs in hot conduits drop a bit more.
Electrical work can kill. Use these numbers for planning and learning; have a licensed electrician do and check any wiring, following your local wiring rules.
Errors and how to fix them
- “Enter the wire size (more than 0)” or “Enter the voltage (more than 0)”: one of these boxes is empty or 0.
- The drop is very large: check that Cable length (one way) is the distance from the supply to the load, not there and back, and that Wire size is in mm² (the size printed on the cable), not its diameter.
Open the tool: Voltage Drop Calculator
Still stuck?
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Questions, or an error not listed here?
Tell us in the comments: what you were doing, the exact message you saw, and your device and browser. We read every comment and add new fixes to this article.