Voltage Drop Calculator
Calculate voltage drop in DC or single-phase AC circuits using conductor material, wire gauge, length, and current. Educational tool with step-by-step solution.
Result
Please check your inputs.
How to Use This Tool
Select the conductor material (copper or aluminum) from the dropdown menu.
Choose the wire gauge (AWG) and circuit type (DC or single-phase AC) to match your installation.
Enter the one-way conductor length (in feet or meters) and the load current (in amperes).
Click 'Calculate' to see the voltage drop result and a detailed step-by-step solution showing resistance, total drop, and percentage.
What Is Voltage Drop Calculator?
Voltage drop is the reduction in electrical potential that occurs as current flows through a conductor. In any circuit, excessive voltage drop can cause equipment to underperform, overheat, or fail. The Voltage Drop Calculator helps electricians, engineers, and students quickly determine whether a given wire size and length will keep voltage loss within safe limits (typically under 3% for branch circuits or 5% for feeders). By adjusting material, gauge, length, and current, you can design efficient and code-compliant installations without guesswork.
Formula
For DC circuits: Vd = 2 × I × L × R, where I = current in amperes, L = one-way length in feet, and R = resistance per foot for the chosen wire. For single-phase AC circuits the same formula applies, assuming the power factor is 1.0. The tool calculates R from the conductor material (copper or aluminum) and AWG gauge using standard resistivity tables, then multiplies by the round-trip distance (2 × L) to find total voltage drop.
Tips for Best Results
🔌 Always account for the round-trip distance—current must travel out and back, so double the one-way length in your calculation.
📏 Use the largest wire gauge that fits your budget and conduit—thicker wire reduces resistance and voltage drop significantly.
🌡️ Remember that resistance increases with temperature; for high-amp or long runs, consider an extra safety margin of 10–15%.
🔍 Verify your load current is accurate—using a clamp meter on the actual circuit gives better results than nameplate ratings.
Frequently Asked Questions
What is an acceptable voltage drop percentage?
For most branch circuits, the National Electrical Code recommends no more than 3% drop at the farthest outlet. For feeder circuits, 5% total drop from the service panel to the load is common. Exceeding these limits may cause lights to dim and motors to overheat.
Does the tool work for both copper and aluminum wire?
Yes. Select copper or aluminum from the material list. Aluminum has higher resistivity than copper, so for the same gauge and length, aluminum will produce a larger voltage drop. The tool uses standard resistivity values for each material.
Can I use this calculator for three-phase circuits?
This tool is designed for DC and single-phase AC circuits only. For three-phase, the voltage drop formula changes because current travels on three conductors. You would need a dedicated three-phase calculator for accurate results.