100 Amp Wire Size Calculator

Created by Arturo Barrantes
Reviewed by Wojciech Sas, PhD
Last updated: Oct 11, 2022

The 100 amp wire size calculator will help you determine the appropriate electrical wire for your next whole-house or three-phase equipment installation. Keep reading to find out how to size your cables.

How to calculate the size of a 100 amp wire?

The following information is required before we start:

  • Wire size material since it affects the electrical resistivity.
  • Distance between your energy source and the equipment you want to energize.
  • The voltage at which your system will run.
  • System configuration: Single-phase / Three-phase

Once we have it all, we will use the following formula:

A=2×IϱL×ϕV×%drop,\quad A = \frac{2\times I \varrho L \times \phi}{V \times \%\text{drop}},


  • %drop\%\text{drop} — Allowable voltage drop, in %. For a 100 amps system, keeping a maximum 3% of voltage drop is strongly recommended.
  • VV — Source voltage, measured in volts.
  • II — System current, measured in amperes.
  • ϱ\varrho — Resistivity of the conductor material, measured in ohmmeters;
  • LL — Length of the wire, measured in meters; and
  • ϕ\phi — Phase factor, 1 for AC single phase and 3/2\sqrt{3}/2 for AC three-phase.
  • AA — Cross-sectional wire area measured in square meters.

The result will be expressed in mm² (if using the metric system).

It is common for wires to indicate their size in AWG (American Wire Gauge) units. Our wire gauge calculator relates circular cross area in mm² to AWG, but do not worry; our 100 amp wire size calculator also provides results in AWG.

How do you use this 100 amp wire size calculator?

To find the wire size suitable for your application, follow these steps:

  1. Verify your connection will be a 100 amp alternate current.
  2. Choose the electrical system configuration: single or three-phase. Then, specify the voltage source.
  3. Define the wire material you will use, the operating temperature, and the voltage drop.
  4. Finally, input the length of your cable (remember, it's a one-way distance).

As a result, the 100 amp wire size calculator will indicate the cross area of the cable you need to install.

Other useful tools like the 100 amp wire size calculator

Since you already know how to size a 100 amp wire, you can take a look at other calculators:


What size wire do I need for 100 amps?

It will depend on the system voltage and the distance between the feeder and equipment. Our Omnicalculator 100 amps wire size tool indicates that for 100 feet, 110 volts (three-phase), you should consider a 2 AWG cable.

How many watts is 100 amps?

8,800 watts to 18,400 watts in a single-phase system (110 volts to 230 volts) with a power factor of 0.8. We used the formula:

Power = Phase current × Phase voltage × Power factor

Try the Omnicalculator 100 amps wire size tool to get the proper wire you should install.

Arturo Barrantes
Electrical system
AC Single-phase
Source voltage
Allowable voltage drop (V)
Conductor material
One-way distance (D)
Maximum wire temperature
Recommended wire size per cable
Wire gauge
Wire cross-sectional area (A)
Wire diameter (d)
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