Cable Sizing / Maximum Distance Calculator

Excessive voltage drop makes it difficult to push current through power cables. 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 a 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. This cable sizing tool suggests THHN, which is appropriate for standard industrial applications. Wire selection must be in compliance with NEC Code Article 300.

Solving for

Matched Cable Size Required
EU Size (mm2)
AWG Size
(1) All cable sizes given on this page refer to single core THHN PVC insulated cable, at an ambient temperature of 30 deg C, and a conductor temperature of 83 deg C max.
(2) This cable size calculator should be used as a guideline only. Punchlist Zero accepts no liability for compliance to local and national building codes.

(3) Product selection recommendations include a 20% upsizing from calculated length. Always ensure physical realities are taken into account when performing a cable run.
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.