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Voltage drop calculator

Check voltage drop for a wire run and load from figures you type.

Jump to the result
Wire run

One run, one load.

Supply (required)

Single-phase includes a round trip. Three-phase uses 1.732.

Metal (required)

Copper fills 0.017241. Choose Custom to type another resistivity.

m

The distance from the source to the load, not the round trip.

A

The load current. Type 0 for no load.

mm²

Cross-section of one conductor. Greater than 0.

V

The supply voltage. Greater than 0. Used for the percent.

Ω·mm²/m

Ohm millimetres squared per metre. Copper at 20 °C is 0.017241. Up to 6 decimal places.

Result

Voltage drop calculator

Supply (required)
Single-phase or DC
Metal (required)
Copper
Resistivity (required)
0.017241

Enter a length, a current, a wire area and a voltage to see the drop.

Single-phase and DC: drop = 2 × current × one-way length × resistivity ÷ area. Three-phase: replace 2 with 1.732. Resistivity is ohm·mm²/m, length is metres, area is mm², current is amperes.

Copper starts at 0.017241 ohm·mm²/m, which is 1/58 at 20 °C from IEC 60028 (International Annealed Copper Standard). Three-phase uses 1.732 (1732/1000). Verify with a licensed electrician and the Canadian Electrical Code.

Estimate for planning only. This is not tax, legal, accounting or financial advice. Results depend on the figures you enter. Check all numbers, rates and rules with the official source or a qualified professional before relying on them.

How this works and common questions

About this tool

This uses the resistivity formula below. Verify with a licensed electrician and the Canadian Electrical Code. Nothing is stored.

How it works

The drop is 2 × current × one-way length × resistivity ÷ area for single-phase and DC. Three-phase uses 1.732 instead of 2. Percent drop is the rounded drop divided by the voltage you type. One-way resistance is resistivity × length ÷ area.

Rules

Copper starts at 0.017241 ohm·mm²/m from IEC 60028 at 20 °C. Other metals, including aluminum, are a resistivity you type. This is not a Canadian Electrical Code wire-size table. Verify with a licensed electrician and the Canadian Electrical Code. Nothing is stored.

Single-phase and DC: drop = 2 × current × one-way length × resistivity ÷ area. Three-phase: replace 2 with 1.732. Resistivity is ohm·mm²/m, length is metres, area is mm², current is amperes.

Questions

What formula does it use?

Single-phase and DC use 2 × I × L × ρ ÷ A. Three-phase uses 1.732 × I × L × ρ ÷ A. ρ is the resistivity you see in the field.

Where does the copper number come from?

0.017241 ohm·mm²/m is 1/58 at 20 °C, from IEC 60028, the International Annealed Copper Standard. You can type over it.

Does it pick a wire size from the Code?

No. You type the area. Verify with a licensed electrician and the Canadian Electrical Code.

Do I need an account?

No. The tools work without one. You only need to sign in to save your work.

Is what I type saved?

Not saved. Copy or print before you leave this page.

Do you show ads or sell my information?

No. We show no ads and we do not sell your information.

Is this tax or legal advice?

No. Results are estimates for planning. Check rates and rules with the official source or a qualified professional.

Not saved. Copy or print before you leave this page.

Estimate for planning only. This is not tax, legal, accounting or financial advice. Results depend on the figures you enter. Check all numbers, rates and rules with the official source or a qualified professional before relying on them.