Voltage drop
Estimates resistive volts lost across the circuit.
Enter supply voltage, load current, one-way length, conductor resistance, and system type to estimate resistance-only voltage drop.
Single-phase drop = 2 x length x amps x resistance per 1,000 ft / 1,000. Three-phase drop = square root of 3 x length x amps x resistance per 1,000 ft / 1,000.
Estimates resistive volts lost across the circuit.
Shows estimated drop as a share of supply voltage.
Subtracts estimated drop from supplied voltage.
This calculator estimates resistive voltage drop from one-way conductor length, current, and conductor resistance stated in ohms per 1,000 feet. It applies a round-trip factor of two for a single-phase circuit and the square root of three for a simplified three-phase line-to-line estimate.
Use conductor resistance that matches the material, wire size, temperature basis, and unit system of your scenario. The result is only as useful as that input. This tool does not look up wire tables, infer conductor size, or determine whether a selected voltage-drop percentage is acceptable for a particular installation.
Real designs can require reactance, ambient and conductor temperature, terminal conditions, parallel conductors, load type, fault-current constraints, grounding, overcurrent protection, equipment instructions, and local code. A qualified electrician must verify any electrical design before work is performed.
| Input | What it means | Planning note |
|---|---|---|
| Supply voltage | Nominal system voltage | Use the relevant line or line-to-line value. |
| Load current | Current used in the scenario | Starting and harmonic current may differ. |
| One-way length | Source-to-load conductor path in feet | Do not enter round-trip length for the single-phase formula. |
| Resistance | Conductor ohms per 1,000 ft | Match material, size, and temperature assumptions. |
Compare a proposed conductor path length.
See how current or conductor resistance changes the estimate.
Understand the relationship between resistance, length, current, and voltage loss.
Enter the one-way source-to-load length in feet. The single-phase formula applies the return-path factor.
No. You must provide resistance; this page does not perform a code-compliant conductor selection.
The simplified three-phase relationship uses the square root of three rather than the single-phase round-trip factor.
No. A qualified electrician must verify the complete installation and applicable requirements.
Last reviewed: October 4, 2026. Electrical estimates are educational planning tools, not installation instructions. A qualified electrician must verify conductor, protection, voltage drop, grounding, equipment, and local code requirements.
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