DC Voltage Drop Calculator
Estimate voltage drop and cable power loss in a two-wire DC circuit from current, cable length, and conductor size.
Your result
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How to use this calculator
- Enter your values in the labeled fields, keeping the displayed units.
- Choose Calculate or press Enter in a single-line field.
- Review the result and the assumptions below before using it.
Formula and method
Loop resistance = 2 × one-way length × resistivity / cross-section. Drop = current × loop resistance.
Worked example
Using copper resistivity 0.01724 Ω·mm²/m, a 10 m one-way, 2.5 mm² cable at 5 A drops about 0.6896 V.
What the result assumes
Uses copper 0.01724 and aluminum 0.0282 Ω·mm²/m at 20°C. This is a DC estimate, not an ampacity or electrical-code compliance check.
Common question
Why is cable length multiplied by two?
Current travels to the load and returns, so a two-wire circuit has twice the one-way conductor length.