Wiring Voltage Drop
Estimate the voltage drop over a length of wire.
About Wiring Voltage Drop
Voltage drop grows with the round-trip wire length and current. Comparing it to the system voltage as a percentage shows whether it stays within a typical three percent limit. Excessive voltage drop wastes energy and can starve equipment, so it must be checked on long or high-current runs.
Formula
Wiring Voltage Drop
Voltage drop = 2 x length x current x resistance / 1000
- resistance
- Ohms per 1000 feet for the wire gauge
Worked example
With the default values below, Wiring Voltage Drop returns Voltage Drop of 2.97. Change any input above and every figure here is recalculated in your browser.
Inputs used
- One-way length
- 50 ft
- Current
- 15 A
- System voltageminimum 1 V
- 120 V
- Resistance per 1000 ftminimum 0 ohms
- 1.98 ohms
Results
- Voltage Drop
- 2.97 V
- Drop Percentage
- 2.48%
- Voltage Drop Check
- Within the common 3% limit
Step by step
- 1Values used
- 2Wiring Voltage Drop
- 3Voltage Drop= 2.97 V
- 4Drop Percentage= 2.48
- 5Voltage Drop Check= Within the common 3% limit
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Wiring Voltage Drop calculated?
Voltage drop = 2 x length x current x resistance / 1000 Voltage drop grows with the round-trip wire length and current. Comparing it to the system voltage as a percentage shows whether it stays within a typical three percent limit.
Why does Wiring Voltage Drop matter?
Excessive voltage drop wastes energy and can starve equipment, so it must be checked on long or high-current runs.
What values do I need to enter?
This calculator takes 4 inputs: One-way length, Current, System voltage, Resistance per 1000 ft. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.