Voltage Drop Calculator
Fill in the values and the answer updates as you type.
How the Voltage Drop Calculator works
Voltage drop = k × resistivity × length × current ÷ cross-section, with k = 2 for single-phase (out and back) and √3 for three-phase. Resistivity is 0.0175 Ω·mm²/m for copper and 0.0282 for aluminium at about 20 °C. Many codes recommend keeping total drop under 3–5%. For three-phase, enter the line-to-line voltage. Example: with the default values, voltage drop comes to 5.25 V.
Inputs and results
The Voltage Drop Calculator takes 6 inputs and gives 4 results.
What you enter
- Supply voltage (V) — starts at 230.
- Load current (A) — starts at 20.
- One-way cable length (m) — starts at 30.
- Conductor cross-section (mm²) — starts at 4.
- Conductor material — starts at Copper. Choose from: Copper and Aluminium.
- Supply type — starts at Single-phase. Choose from: Single-phase and Three-phase.
What you get
- Voltage drop (V)
- Voltage drop
- Voltage at the load (V)
- Cable power loss (W)
Example: Voltage Drop Calculator with the starting values
With supply voltage 230 V, load current 20 A, one-way cable length 30 m, conductor cross-section 4 mm² and conductor material Copper, the calculator returns:
| Voltage drop (V) | 5.25 |
|---|---|
| Voltage drop | 2.28% |
| Voltage at the load (V) | 224.8 |
| Cable power loss (W) | 105 |
Change any value above and the results update straight away.
Voltage Drop Calculator FAQ
How do I use the Voltage Drop Calculator?
Enter supply voltage, load current, one-way cable length and conductor cross-section in the fields, then read voltage drop (v), voltage drop, voltage at the load (v) and cable power loss (w) in the result panel. The answer updates as you type, and you can press Calculate or Enter to refresh it. Use “Copy link” to share your exact numbers with someone else.
What does the Voltage Drop Calculator calculate?
Voltage drop and power loss along a cable. It returns voltage drop (v), voltage drop, voltage at the load (v) and cable power loss (w) from the 6 values you provide.
What values does the Voltage Drop Calculator start with?
It opens with supply voltage 230 V, load current 20 A, one-way cable length 30 m and conductor cross-section 4 mm² so you can see a working result straight away. Replace them with your own numbers, or press Reset to return to these starting values.
Is the Voltage Drop Calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so nothing you type is sent to or stored on our servers. See the Privacy Policy for details.
Can I rely on the Voltage Drop Calculator for important decisions?
Treat the result as a well-rounded estimate. Real situations often have details a general calculator cannot know, so confirm important decisions with a qualified professional. See the Disclaimer for more.