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Voltage Drop Calculator
Voltage Drop Calculator
Calculate wire voltage loss β NEC compliance, wire sizing & efficiency
Vdrop = I × R | R = ρ × (2L / A) | NEC recommends ≤ 3% drop
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Voltage Drop
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Received Voltage
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Wire Resistance (R)
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Power Lost
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Drop %0%
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Step-by-Step
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About the Voltage Drop Calculator
Wires have resistance, so voltage falls along their length. Check that a cable run keeps the drop within acceptable limits.
How to use the Voltage Drop Calculator
- Choose the Wire Material and Wire Gauge (AWG).
- Enter the Source Voltage, the Current (Load) and the One-Way Wire Length.
- Press Calculate Voltage Drop.
Formula and method
Voltage drop = I Γ R, where the resistance is R = Ο Γ (2 Γ length) Γ· cross-section area. The length is doubled because current flows out and back. Copper resistivity is about 1.68 Γ 10β»βΈ Ω·m.
Worked example
15 A over 30 m (one way) of 12 AWG copper (3.31 mmΒ²) gives a resistance of 0.30 Ξ© and a drop of about 4.6 V, which is 3.8% of a 120 V supply.
Tips
- A common guideline is to keep the drop below 3% on a branch circuit.
- Use a thicker wire (lower gauge number) or shorter run to reduce the drop.
- Follow your local electrical code, and use a qualified electrician for installations.
Frequently Asked Questions
Copper conducts better, so a copper wire drops less voltage than an aluminium wire of the same size.