Voltage drop over a cable run, with a pass/fail against the 3% guideline.
How to use this calculator
Every field updates the result as you type — there is no submit step. The inputs below are pre-filled with a realistic example so you can see how the tool behaves before entering your own figures.
| Field | Unit | What it means |
|---|---|---|
| Source voltage | V | Enter a numeric value. |
| Load current | A | Enter a numeric value. |
| One-way cable length | m or ft | Enter a numeric value. |
| Conductor cross-section | mm² | Enter a numeric value. |
| Conductor | — | Select the mode that matches your situation. |
| System | — | Select the mode that matches your situation. |
| Length unit | — | Select the mode that matches your situation. |
Worked example
Using the default values loaded into the calculator above, the result is:
| Input | Value |
|---|---|
| Source voltage (V) | 240 |
| Load current (A) | 20 |
| One-way cable length (m or ft) | 50 |
| Conductor cross-section (mm²) | 4 |
| Conductor | Copper |
| System | Single phase |
| Length unit | Meters |
| Output | Value |
|---|---|
| Voltage drop | 8.6 V |
| Voltage at load | 231.4 V |
| Conductor resistance (one way) | 0.215 Ω |
| Power lost in cable | 172 W |
| Cable length used | 50 m |
| Minimum size for 3% drop | 4.778 mm² |
Reading the result
Conversion factors and physical constants used here are the standard published values. Where a result depends on a material property, local code or regional convention, that value is exposed as an input so you can match it to your situation.
For construction and electrical work, always verify against the codes that apply in your jurisdiction.
Sharing and saving a calculation
The "Copy link" button encodes every value you have entered into the page URL. Opening that link restores the calculation exactly, which makes it easy to bookmark a scenario, send it to someone else, or keep several variations side by side in separate tabs.
Frequently asked questions
What does the Voltage Drop Calculator do?
Voltage drop over a cable run, with a pass/fail against the 3% guideline.
What result do the default values produce?
With the values pre-loaded in the calculator, voltage drop comes to 8.6 V.
Is this calculator free to use?
Yes. It is free, requires no account, and runs entirely in your browser — nothing you enter is transmitted or stored on a server.
Can I save or share a calculation?
Yes. The "Copy link" button builds a URL containing all your entered values. Anyone opening that link sees the same calculation.
How accurate is the result?
The calculation itself is exact for the inputs given. Real-world accuracy depends on how well those inputs reflect your actual situation, so review the assumptions before relying on the figure.