DC Voltage Drop Calculator

DC power planning tool

Calculator controls and results

See how current, wire size, and cable length affect the voltage reaching your radio or equipment.

System voltage
Current draw (amperes)

Larger conductors have smaller AWG numbers.

Enter source-to-equipment distance. The return conductor is included automatically.

Advanced circuit details
Circuit length mode

Additional resistance can represent measured or specified connectors, fuse holders, switches, relays, or terminals. No generic connection value is assumed.

Wire size comparison (same voltage, current, and run)

i

Annealed-copper resistance at 20 °C from NIST Copper Wire Tables. Actual resistance changes with conductor construction and temperature.

View calculation method and source

Vdrop = I × Rloop; Ploss = I² × Rloop. Basic mode doubles the one-way run for positive and return conductors. NIST Bureau of Standards Circular 31.

Planning DC power wiring for radio equipment

Voltage drop is the difference between the voltage at the power source and the voltage that reaches equipment while current is flowing. A two-conductor DC circuit includes resistance in both the positive and return conductors, so the calculator turns the entered one-way distance into a complete conductor loop.

Why transmit current matters

Radio current is often much higher during transmit than receive. A radio that receives substantially less voltage during transmit may not operate under the same conditions it does at the source, although the exact response depends on the equipment.

Voltage drop is not an ampacity approval

The score describes voltage-drop performance only. Conductor ampacity also depends on insulation, construction, bundling, ambient conditions, installation method, temperature rating, and applicable standards. Proper overcurrent protection is still required.

Methodology

The default copper table uses International Annealed Copper Standard resistance at 20 °C. The calculator adds optional circuit resistance, calculates voltage drop with Ohm’s law, and calculates wiring heat loss with I²R. It does not apply undocumented connector or temperature assumptions.

Related RF planning tools

Convert RF power between dB, dBm, dBW, and watts, or calculate RF loss between the radio and antenna.