Cable Sizing / Maximum Distance Calculator

Excessive voltage drop makes it difficult to push current through a circuit. This can lead to an increase in energy consumption, overheating, and even the shortening of equipment life. Under voltage may also cause computers, printers, and sensitive electric equipment to shutdown.

The NEC Code Book recommends that the maximum combined voltage drop for both the feeder and branch circuit shouldn’t exceed 5%, and the maximum on the feeder or branch circuit shouldn’t exceed 3% . This calculator allows for the selection of voltage drop of up to 3% on a circuit run. Minimum cable size can be calculated based on cable length, voltage, amperage, and acceptable loss. For additional reference, purchase an Ugly’s Reference Book.

Solving for

Matched Cable Size Required
EU Size (mm2)
AWG Size
(1) All cable sizes given on this page refer to single core HO7RNF rubber insulated cable, at an ambient temperature of 30 deg C, and a conductor temperature of 85 deg C max.
(2) Cable sizes should only be used as a guideline and if not using HO7RNF cable, all figures should be checked against the manufacturers data sheet. Also, all cables should be fused / current protected to their max rating or less.
(3) All information is provided in good faith. Punchlist Zero accepts no liability for damages of any kind, directly or indirectly caused by the use of this calculator.
Maximum Circuit Distance
Length (ft)
Voltage Drop
Voltage at Load
(1) Note: The results of this calculator are based on conductor temperatures of 75°C.
(2) Source: NFPA 70, National Electrical Code, Chapter 9, Table 8.