Home / Tech / Voltage Drop Calculator
Voltage Drop Calculator
Calculate the voltage drop in a DC circuit to ensure your wire gauge is sufficient for the distance and load.
Circuit Details
Results
Understanding Voltage Drop
What is Voltage Drop?
Voltage drop is the reduction in voltage as electrical current flows through a conductor (wire). It's caused by the wire's resistance, which converts electrical energy into heat. The longer or thinner the wire, the greater the resistance and voltage drop.
Voltage Drop (V) = Current (A) × Resistance (Ω)
Resistance (Ω) = Wire Resistance per km × (Total Length in km)
For example: A 12V circuit with 10A current through 10m of 14 AWG copper wire (round-trip resistance ~0.17Ω) has a voltage drop of 1.7V, leaving only 10.3V at the load.
Why Does It Matter?
Excessive voltage drop causes:
- LED lights: Flickering, dimming, or color shift
- Motors: Overheating, reduced torque, premature failure
- Electronics: Malfunction, unexpected shutdowns
- Heaters: Reduced heat output, inefficiency
- Charging: Incomplete battery charging
💡 Expert Tip: Sizing for Solar & RV Systems
For 12V/24V solar and RV systems, aim for under 2% voltage drop for critical loads. Battery charging is voltage-sensitive—a few tenths of a volt can mean the difference between full charge and 80% charge. For long runs (10m+), consider stepping up to 24V or 48V to reduce current and improve efficiency. Use 2 AWG or larger for high-current inverter connections.
⚠️ Common Mistake: Forgetting Round-Trip Distance!
Many people calculate voltage drop for one-way distance only. In DC circuits, current travels OUT through the positive wire and BACK through the negative wire—so you must count the total wire length (distance × 2). A 5-meter cable run is actually 10 meters of wire.
Acceptable Limits
For most low-voltage DC circuits, a voltage drop of 3% or less is recommended. For critical circuits (electronics, LEDs), aim for under 2%. The NEC recommends:
- Branch circuits: 3% maximum (AC systems)
- Feeders: 2% maximum (AC systems)
- Low voltage DC: 2-3% for best performance
AWG Wire Gauge Quick Reference
Lower AWG number = thicker wire = less resistance
- 18 AWG: Low current (<2A), short distances (LED strips, signals)
- 14 AWG: 5-10A, medium distances (12V lighting, small motors)
- 10 AWG: 10-20A, longer runs (12V high-power LED, pumps)
- 6 AWG: 20-40A (solar charge controllers, inverters)
- 2 AWG: 40-80A (battery banks, high-power inverters)
Reviewed by: Michael Torres, Licensed Electrician
Last updated: November 27, 2025
Frequently Asked Questions
What is voltage drop?
Voltage drop is the reduction in voltage as electrical current flows through a wire. It's caused by the resistance of the conductor. Longer or thinner wires cause more voltage drop.
What is an acceptable voltage drop?
For most low-voltage DC circuits, 3% or less is recommended. For example, on a 12V circuit, the maximum drop should be 0.36V. For critical loads, aim for under 2%.
What wire gauge should I use?
Wire gauge depends on current, distance, and acceptable voltage drop. Lower AWG = thicker wire = less resistance. Always calculate for your specific application.
Why does wire length matter?
Voltage drop is proportional to wire length. In DC circuits, remember to count round-trip distance (positive + negative wire). A 5-meter run = 10 meters total wire length.