How it works
Calculate voltage drop in a wire run (Single Phase).
Input query strings and outputs
Use an input name in this page’s URL as ?name=value, and join additional inputs with &. Portable shared links may instead use the compact ?ac= state parameter.
Input query strings
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?voltage=Source Voltage (V)Number · Optional · Default: 120
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?current=Load Current (Amps)Number · Optional · Default: 10
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?distance=One-way Distance (Feet)Number · Optional · Default: 50
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?wireSize=Wire SizeText · Optional · Default: 14
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?material=MaterialText · Optional · Default: copper
Outputs
1-
resultResultText · Primary output
result contains the calculator’s complete rendered result area, including its visible result cards, tables, charts, and messages.
Calculate electrical energy loss over a long wire run
Description
The Voltage Drop Calculator is a critical engineering and safety tool for electricians and DIYers. When electricity travels through a wire, some of the energy is lost as heat due to the wire’s natural resistance. If the wire is too thin or the distance is too long, the voltage at the end of the run might be too low to safely power your devices. This tool calculates the Voltage Drop, the Final Voltage, and the Percentage Loss for single-phase circuits.
Inputs
- Source Voltage (V): The voltage at the breaker or power source (e.g., 120V or 240V).
- Load Current (Amps): The amount of electricity the device draws.
- One-way Distance (Feet): The length of the wire from the source to the device.
- Wire Size (AWG): The thickness of the wire (American Wire Gauge).
- Material: Select Copper (standard) or Aluminum.
Outputs
- Voltage Drop: The amount of voltage lost during transmission.
- Voltage at Load: The actual voltage available to the device.
- Percent Drop: The percentage of the source voltage that was lost.
Chart
- N/A: This tool provides precision numeric electrical results.
“Good to Know”
- The 3% Rule: The National Electrical Code (NEC) recommends a maximum voltage drop of 3% for branch circuits to ensure optimal performance and safety. If your result is in the red, consider using a larger (thicker) wire.
- Resistance: Thicker wires (lower AWG numbers) have less resistance and therefore less voltage drop.
- Distance: Voltage drop increases linearly with distance. Doubling the length of the wire doubles the voltage lost.
- Single Phase: This calculator assumes a standard 2-wire (plus ground) single-phase circuit.
Examples
Example 1: Outdoor Shed Light
- Input: 120V, 5 Amps, 100 ft, 14 AWG, Copper
- Output: 2.53 V Drop (2.10%) - Safe
Example 2: Long Run Power Tool
- Input: 120V, 15 Amps, 200 ft, 12 AWG, Copper
- Output: 9.53 V Drop (7.94%) - Warning: Too High!
Example 3: Subpanel Feed
- Input: 240V, 50 Amps, 150 ft, 4 AWG, Aluminum
- Output: 6.15 V Drop (2.56%) - Safe