Estimate voltage loss for AC and DC circuits over long distances. Find the right copper or aluminum wire size to maintain steady power and meet common safety recommendations.
Voltage drop is a common issue that causes equipment failure, poor performance, and wasted energy in electrical systems. We built this calculator so professionals and DIYers can quickly check their wire sizes against standard safety guidelines without doing complex manual math involving conductor resistivity and circular mils.
The tool takes your input values and applies standard electrical formulas based on Ohm's Law. It uses the specific resistance properties of copper and aluminum to figure out how much power is lost over your required distance. Once it calculates the exact voltage dropped, it compares the result to the commonly accepted National Electrical Code limits of 3% for branch circuits and 5% for total systems, changing color to warn you if your setup is inefficient.
This tool provides estimates based on standard ambient temperatures and ideal conditions using National Electrical Code Chapter 9, Table 8 values. Actual voltage drop in the real world can vary based on conduit material, the quality of your terminal connections, and extreme temperature fluctuations. Always consult a licensed electrician or engineer to finalize your project plans.
Select whether your system is AC or DC, and choose Single Phase or Three Phase. Most residential home circuits are Single Phase AC, while large industrial motors use Three Phase AC.
Choose your conductor material. Copper is standard for inside wiring, while aluminum is often used for long exterior service runs. Select the wire gauge you intend to use.
Enter the one-way length of the wire run from the power source to the device. Enter the total load current in Amps, and the starting source voltage.
Adjust the Power Factor or Temperature if you are calculating for specific environmental conditions or inductive loads.
Click "Calculate Voltage Drop". If the result shows a warning for exceeding 3% or 5%, try selecting a thicker wire size.
Voltage drop is the loss of electrical pressure as current flows through a wire. Every wire has some internal resistance that opposes the flow of current. You can visualize this like water in a long hose. The water pressure at the spigot is high, but friction against the hose walls reduces the pressure by the time it reaches the end. In electrical systems, that lost pressure is converted into heat along the wire.
The National Electrical Code provides recommendations to keep electrical systems efficient. For branch circuits, the recommendation is a maximum drop of 3%. This ensures devices receive at least 97% of their rated voltage. For feeder circuits, the limit is also 3%. The combined total drop of the feeder plus the branch circuit should not exceed 5%.
If your calculation shows a high percentage drop, you have a few practical options. The most common fix is to upsize the wire. While a thicker wire costs more upfront, it saves energy and protects your equipment in the long run. You can also try shortening the physical distance of the wire run or switching from aluminum to copper wire for better conductivity.
Yes, but usually only slightly. In AC systems, running wires through steel conduit can increase voltage drop because of magnetic effects known as inductive reactance. PVC or aluminum conduit does not cause this issue. For typical home circuits, the difference is very small, but it matters for large commercial feeders.
LEDs and incandescent bulbs are sensitive to voltage changes. When a heavy load like a refrigerator or air conditioner starts up, it draws a massive spike of current. This sudden current draw causes a temporary voltage drop across the shared circuit, resulting in a brief dimming or flickering of the lights.
In standard residential or commercial settings, you cannot safely increase the source voltage beyond the utility provider's standard levels. The safest and most reliable way to fix a voltage drop issue is to reduce the resistance by installing thicker wires or shortening the wire run.
Running a system with a drop over 5% means your equipment is constantly fighting low voltage. Motors will run hotter and wear out faster, lights will perform poorly, and energy is actively wasted as heat within your wiring infrastructure.
Copper is a more efficient conductor, so you can use a smaller wire size compared to aluminum for the same distance. However, aluminum is much lighter and less expensive. Electricians often use aluminum for very long, heavy feeder runs to save money, compensating for the higher resistance by using a thicker gauge.