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Voltage Drop Calculator

Estimate voltage drop from conductor material, one-way run length, current, cross-sectional area and supply voltage. AC modes can include a power factor.

Resistive-only estimate using nominal material resistivity at 20°C. It omits conductor heating, AC reactance, harmonics, connections, installation conditions and code requirements; actual drop can be higher. Three-phase mode assumes balanced load; AC power factor scales only the resistive term. Not cable sizing, ampacity, protection, compliance or electrical safety advice. Have a qualified electrician verify the design against local rules and manufacturer data.

How do I estimate voltage drop in a wire?

Choose the circuit and conductor material, then enter the one-way route length, current, conductor area and supply voltage. For a resistive single-phase copper example at 20°C, 20 A over 30 m with 2.5 mm² at 230 V is about 8.27 V or 3.60%.

Frequently asked questions

How do I estimate voltage drop in a wire?

Choose the circuit and conductor material, then enter the one-way route length, current, conductor area and supply voltage. For a resistive single-phase copper example at 20°C, 20 A over 30 m with 2.5 mm² at 230 V is about 8.27 V or 3.60%.

Are my electrical inputs uploaded?

No. The estimate runs in your browser; entered values are not sent to a server by this tool.

Does this calculate the correct wire size?

No. It estimates resistive voltage drop for entered values. Safe conductor sizing also depends on ampacity, insulation, installation method, ambient temperature, grouping, fault protection, terminals and local electrical codes.

Why might the real voltage drop be higher?

Conductor resistance rises as it heats. This estimate uses a reference material resistivity at 20°C and omits AC reactance, harmonics, connectors and installation details.

What does one-way length mean?

Enter the distance from the supply to the load once. The DC and single-phase formulas account for the outgoing and return conductors; balanced three-phase uses its standard square-root-of-three resistive approximation.