Using the Voltage Drop Calculator
Cable length is the one-way distance; the formula doubles it to include the return conductor. Cross-section is in square millimeters, not diameter. Material selects an approximate resistivity at twenty degrees Celsius, and the current is treated as fixed.
Worked example
Use the example inputs below to reproduce this result. These are the form's starting values, not recommended targets. Changing your inputs updates your result above; this worked example stays fixed for comparison. Results are rounded for display.
Example inputs
- Supply voltage (V)
- 24
- Load current (A)
- 10
- One-way cable length (m)
- 20
- Conductor cross-section (mm²)
- 2.5
- Conductor
- Copper
Example result
- Voltage drop (V)
- 2.75856
- Voltage drop (%)
- 11.494
- Estimated load voltage (V)
- 21.24144
Method and assumptions
Vdrop = I × resistivity × round-trip length / area, using approximate resistivity at 20°C. Excludes AC reactance, temperature correction and installation-code sizing.
Distinguish a model from a circuit specification
Electrical calculations describe the assumptions entered in the form. Real components, cables and supplies also have ratings, tolerances and operating conditions. Confirm whether the model is for DC resistance, energy over time or another specific quantity. A mathematically consistent result is not by itself a complete design or installation check.
Common question
Should I enter the combined outgoing and return length?
No. Enter the one-way cable length because the model already doubles it. Entering the combined length would count the return path twice and overestimate the voltage drop for this two-wire model.
Guide updated .