100 Amp Wire Size Calculator
Preset to 100 A. Adjust run length, supply voltage, drop %, and material.
How to Use This Calculator
This tool is preset for 100 A loads. Adjust one-way cable length, supply voltage (e.g., 120/240 V), allowable voltage drop percentage, and conductor material. Click Calculate to find the minimum cross-sectional area.
- Enter the one-way length (the calculator accounts for the return path).
- Typical allowable drop: 3% for feeders/branch circuits.
- Verify thermal ampacity separately per code (NEC/IEC).
Formula
Vdrop = I · R = I · (ρ · 2L / A)
A ≥ ρ · 2L · I / Vdrop,allow
This approximation sizes conductors by voltage drop. It does not replace ampacity selection based on insulation, ambient temperature, bundling, or installation method.
Frequently Asked Questions
Does this guarantee code compliance for 100 A circuits?
No. This calculator only addresses voltage drop. Always check temperature rating, conduit fill, environment, and local code tables for ampacity.
Should I enter round-trip or one-way length?
Enter the one-way length. The computation internally uses 2L to account for the return path.
Can I use aluminum for 100 A?
Yes, but aluminum requires larger cross-section than copper for the same drop and must meet connection and termination requirements.