Voltage Drop Calculator
Calculate voltage drop in electrical circuits.
Circuit Parameters
Volts
Amperes
feet
Ohms per foot
Typical: 12 AWG copper ≈ 0.00193 Ω/ft, 14 AWG copper ≈ 0.00307 Ω/ft
Voltage Drop Results
Voltage Drop
0.200 V
0.17% of source
Voltage at Load
119.800 V
99.83% of source
Power Loss
2.00 W
✓ Acceptable Voltage Drop (<3%)
Within recommended range for branch circuits
About This Calculator
The Voltage Drop Calculator calculates the voltage drop in an electrical circuit based on current, wire length, and resistance. Voltage drop occurs when electrical current flows through a conductor, causing a reduction in voltage from the source to the load.
This calculator is useful for electricians, engineers, and DIY enthusiasts to ensure adequate voltage at the load and to determine if wire size needs to be increased. Excessive voltage drop can cause equipment to malfunction or operate inefficiently.
Note: This calculator assumes single-phase AC or DC circuits. For three-phase circuits, use the appropriate formula. Always consult electrical codes and standards for compliance.
Formula & Calculation Method
Voltage Drop Calculation:
Single-Phase Voltage Drop:
Voltage Drop = 2 × I × R × L
where:
I = Current (amperes)
R = Resistance per unit length (ohms/ft or ohms/m)
L = Length (feet or meters)
Factor of 2 accounts for round trip (hot and neutral)
Voltage at Load:
Voltage at Load = Source Voltage - Voltage Drop
Power Loss:
Power Loss = Current × Voltage Drop
Voltage drop is calculated using Ohm's Law (V = I × R), multiplied by the length of the conductor and a factor of 2 for single-phase circuits (to account for the round trip through both conductors). The resistance depends on wire material, size, and temperature.
How to Use This Calculator
- Enter Source Voltage: Input the supply voltage (e.g., 120V, 240V).
- Enter Current: Input the load current in amperes.
- Enter Wire Length: Input the length of the wire run.
- Enter Resistance: Input the wire resistance per unit length (ohms per foot or meter).
- View Results: See voltage drop, voltage at load, and power loss.
Frequently Asked Questions
What is voltage drop?
Voltage drop is the reduction in voltage that occurs when electrical current flows through a conductor. It happens due to the resistance of the wire, causing a voltage difference between the source and the load.
Why is voltage drop important?
Excessive voltage drop can cause equipment to malfunction, operate inefficiently, or not work at all. Most electrical codes limit voltage drop to 3-5% for branch circuits and 5% for feeders.
How do I reduce voltage drop?
You can reduce voltage drop by: using larger wire (lower resistance), reducing wire length, reducing current load, or using higher voltage. Larger wire has less resistance per unit length.
What is acceptable voltage drop?
Most electrical codes recommend voltage drop not exceed 3% for branch circuits and 5% for feeders. This ensures equipment operates properly and efficiently. Consult local electrical codes for specific requirements.
Calculator by
NumCalculators Editorial Team
Multi-disciplinary Expert Team