Voltage Drop Calculator
Calculate voltage drop, remaining voltage and power loss for DC and single-phase AC circuits.
Calculate Voltage Drop
How the Calculation Works
Voltage drop is calculated from the conductor resistance at the selected temperature:
- V_drop = 2 × L × I × R (round-trip conductor length)
- R is the resistance per meter at the selected conductor temperature (copper or aluminum)
- Percentage drop = V_drop ÷ source voltage × 100%
- Power loss = V_drop × I
Supports both DC and single-phase AC circuits.
Frequently Asked Questions
How much voltage drop is acceptable?
Most 12 V / 24 V automotive and low-voltage systems keep voltage drop below 3-5%. Sensitive loads such as LEDs and sensors may require 2% on long runs.
Why is the length multiplied by 2?
Current travels out to the load and back to the source through two conductors. Voltage drop occurs on both, so the total conductor length is twice the one-way distance.
Does temperature affect voltage drop?
Yes. Copper resistance increases by about 0.39% per °C, so a harness running at 80°C has roughly 20% more resistance than at 20°C.
Can I use this for three-phase AC circuits?
This calculator covers DC and single-phase AC. Three-phase systems use a √3 factor and different formulas; contact our engineers for support.
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