How To Find The Cable Size Formula _best_ Jun 2026

The fundamental formula for voltage drop ($V_d$) is derived from Ohm's Law ($V = IR$), adjusted for the wire's "go and return" path.

Let’s walk through a real example: You need to run a load, 50 meters from the source, using copper cable, and you want to keep the voltage drop under 5V . how to find the cable size formula

Your minimum cable area is 10.5 mm² . Since standard sizes are 10mm² or 16mm², you must round up to 16mm² . The fundamental formula for voltage drop ($V_d$) is

I=PV×PFcap I equals the fraction with numerator cap P and denominator cap V cross cap P cap F end-fraction 50 meters from the source

formula. If the drop is too high, move up to the next cable size. Adjust for heat and bundling.