🧵 Wire Size Calculator
Find the minimum wire size needed for a circuit run based on current, distance, and acceptable voltage drop.
What this calculator does
Choosing an adequately sized wire for a circuit run isn’t just about the current it carries — over long distances, wire resistance itself can cause a noticeable voltage drop. This calculator estimates the minimum conductor cross-section needed to keep that drop within an acceptable limit.
The formula
The required cross-sectional area is found from A = (k × ρ × L × I) / Vdrop, where k is 2 for a single-phase or DC circuit (accounting for the round trip through both conductors) or √3 for a balanced three-phase circuit, ρ is the conductor’s resistivity (in Ω·mm²/m), L is the one-way run length, I is the load current, and Vdrop is the maximum allowable voltage drop in volts (supply voltage × allowed drop percentage).
This is a general planning estimate. Always round up to the next standard commercially available wire size, and verify the result against local electrical codes and the wire’s current-carrying (ampacity) rating, not just its voltage-drop performance.