Voltage Drop Calculator
Calculate DC voltage drop and percent loss for 12 V / 13.8 V ham radio power runs.
HT: ~2–3 A TX · 100 W transceiver: ~20 A TX
Total wire path = 50 ft (both conductors)
Excessive drop — use heavier wire
Voltage Drop
0.794 V
Percent Loss
5.75%
Source voltage13.8 V
Wire resistance (total)0.0794 Ω
Voltage at radio13.006 V
Rule of Thumb
- < 3% — Acceptable for most ham equipment
- 3–5% — Marginal; radio may under-perform on TX peaks
- > 5% — Excessive; risk of under-voltage protection trips
Resistance values from ANSI/NEMA standard copper wire at 20 °C.