Voltage Drop Calculator
Enter current, wire length, wire resistance and supply voltage to estimate two-wire voltage drop, drop % and end voltage.
Input Data
Results
10.4
8.67
109.6
At a glance:Two-wire drop V = 2 × I × L × R ÷ 1000 (I in A, L in m, R in ohm/km). Drop % = V ÷ supply × 100. End voltage = supply − V.
Formula
vDrop = 2 × currentA × lengthM × resistanceOhkm ÷ 1000.
vDropPercent = vDrop ÷ voltageSource × 100.
voltageAtEnd = voltageSource − vDrop.
How to Use
- Enter current, wire length, resistance and supply voltage.
- Get voltage drop, drop % and end voltage instantly.
FAQ
Why multiply by 2?
Current flows out and back on two conductors, so the total loop length is about twice the one-way length.
What drop is acceptable?
Keep line drop under about 3–5% of supply; larger means the wire is too thin and should be upsized.
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References
Content reviewed by the Calculatorism editorial team. Results are for reference only; please refer to the relevant authorities for the official figures.