How to Use the Voltage Drop Calculator
Enter the circuit values to estimate voltage drop, voltage drop percentage, received voltage, and effective circuit resistance. The result also shows the formula, calculation steps, and assumptions used.
- Enter Current, One-way length, and Supply voltage (V).
- Choose Length unit: Feet, Meters, or Centimeters.
- Choose Conductor material and Wire gauge (AWG). Set Conductor temperature (°C).
- Choose Circuit type: DC / single-phase or Three-phase.
- Click Calculate to show the result.
- Click Copy result or Download result (.txt) to save the plain-text output.
Click Reset to clear text inputs, hide the result and errors, restore the default material, gauge, temperature, and circuit type, and set Length unit to Meters.
What the Result Shows
The result includes Voltage drop, Voltage drop %, Received voltage, and Circuit resistance. Circuit resistance is an effective calculated value based on your inputs and circuit type; it is not a measured resistance.
It also includes Formula & steps and Assumptions. A warning appears when voltage drop exceeds 5%. You can copy or download the result as plain text.
Formula and Length Handling
The core formula is:
V_drop = I × R: voltage drop equals current times total circuit resistance.R = ρ(T) / A × L_circuit: resistance uses temperature-adjusted resistivity, conductor area, and circuit length.L_circuit = 2 × L_one-wayfor DC / single-phase, orL_circuit = √3 × L_one-wayfor Three-phase.
Enter the one-way distance from the source to the load. The calculator applies the circuit-specific factor automatically, so do not double the length yourself. Conductor area comes from the standard AWG geometric formula, d(n) = 0.127 × 92^((36−n)/39) mm. Resistivity is adjusted for the selected temperature.
Supported Options
- Length unit: Feet, Meters, or Centimeters
- Conductor material: Copper or Aluminum
- Wire gauge (AWG): 18 AWG through 4/0 AWG
- Conductor temperature (°C): −40°C through 250°C
- Circuit type: DC / single-phase or Three-phase
Validation and Modeling Limits
Current, One-way length, and Supply voltage (V) must be positive numbers. Numeric input must be valid and finite. Conductor temperature (°C) must be between −40°C and 250°C. The calculator also checks that the result is finite.
- It does not check conductor ampacity or apply an electrical code.
- It does not certify wiring or replace review by a qualified, licensed electrician.
- The model uses bulk resistivity, the AWG geometric formula, constant conductor temperature, unity power factor, and no reactance, skin effect, connector, terminal, or splice resistance.
Privacy and Page Data Handling
The voltage-drop calculation runs locally in your browser. This page also loads normal site analytics and includes a subscription form that submits to /assets/subscribe.php.
Frequently Asked Questions
What formula does this voltage drop calculator use?
It uses V_drop = I × R, where R is the total circuit resistance. R uses temperature-adjusted conductor resistivity divided by cross-sectional area from the standard AWG diameter formula, multiplied by 2 × the one-way length for DC / single-phase circuits or √3 × the one-way length for Three-phase circuits.
Do I enter one-way or round-trip wire length?
Enter the one-way length of the run - the distance from the source to the load. The calculator automatically applies the round-trip factor for DC and single-phase circuits, or the square-root-of-3 factor for three-phase circuits, so you should not double the length yourself.
What is an acceptable voltage drop percentage?
Many design guidelines target 3% or less for a branch circuit and 5% or less total from source to load, but the acceptable value depends on the equipment and the electrical code that applies in your jurisdiction. This calculator flags drops above 5% as high but does not apply any specific code.