Voltage Drop Calculator for Building Circuits
Calculate approximate resistive voltage drop for copper or aluminium conductors and compare it with an editable design percentage.
Estimate building-circuit voltage drop
Calculate approximate resistive voltage drop for copper or aluminium conductors and compare it with an editable design percentage.
How the voltage drop calculator for building circuits works
The tool estimates conductor resistance from resistivity, length and cross-sectional area, with a simple temperature adjustment. A two-wire/single-phase circuit uses twice the one-way resistance; a balanced three-phase circuit uses √3 times the one-way resistance. Voltage drop percentage is drop divided by nominal voltage.
Where this construction calculation helps
Use it as an early conductor-sizing cross-check before detailed electrical design.
Measurements and assumptions
This model focuses on conductor resistance. Real AC circuits may require impedance, reactance and power-factor treatment. Ampacity, fault protection, grounding, derating, harmonics and installation methods must be checked separately against the applicable electrical code. The comparison percentage is editable rather than presented as a universal legal limit.
Worked example
For a 230 V single-phase circuit, longer cable runs or smaller conductor area increase resistance and therefore voltage drop for the same current.
Use voltage drop as one part of conductor selection
A building-circuit voltage drop calculator estimates the reduction in voltage caused by conductor resistance over a specified run. It is useful for comparing conductor sizes and identifying long circuits that may need closer review, but voltage drop is only one design constraint. Ampacity, insulation rating, installation method, ambient temperature, grouping, fault protection, earthing and local electrical code can govern the final cable size. Treat the entered voltage-drop limit as a design target and have regulated electrical work checked by a qualified professional.