AC/DC Voltage Drop Calculator & Formula

How is the Voltage Drop Formula Calculated?

The voltage drop formula is calculated by multiplying the circuit’s current by the conductor’s total resistance. Our dc voltage drop calculator allows you to choose your conductive material (copper or aluminum), select the American wire gauge (AWG) size, enter the one-way circuit (foot length) and load amount (in amperes). This will calculate your voltage drop, voltage at load end of the circuit, the percent voltage drop and CMA of the conductor.

Our dc voltage drop calculator uses K = 12.9 circular mil ohms per foot for copper or K = 21.2 circular mil ohms per foot for aluminum. These values assume a conductor operating temperature of 75 degrees C. For other values of K based on conductor temperature use the advanced dc voltage drop calculator.

DC Voltage Drop Calculator

Select Material Copper Aluminum	Select Size 18 AWG 16 AWG 14 AWG 12 AWG 10 AWG 8 AWG 6 AWG 4 AWG 3 AWG 2 AWG 1 AWG 1/0 AWG 2/0 AWG 3/0 AWG 4/0 AWG 250 kcmil 300 kcmil 350 kcmil 400 kcmil 500 kcmil 600 kcmil 700 kcmil 750 kcmil 800 kcmil 900 kcmil 1000 kcmil 1250 kcmil 1500 kcmil 1750 kcmil 2000 kcmil
Select Voltage and Phase 120 Volts 1-phase 240 Volts 1-phase 208 Volts 3-phase 3-wire 120/208 Volts 3-phase 4-wire 277 Volts 1-phase 480 Volts 3-phase 277/480 3-phase 4-wire 600 Volts 3-phase 24 DC or 1-phase AC 48 DC or 1-phase AC 124 DC or 1-phase AC
Enter 1-way circuit (length in feet)	Enter Load (in amperes)
Voltage drop	Voltage at load end of circuit
Per Cent voltage drop	cma of conductor

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What is Voltage Drop?

Voltage drop is the amount of voltage loss that occurs in either part or all of a circuit due to impedance. Voltage drops that are too low can result in poor performance of a product and can even damage electrical equipment if severe enough. While the National Electric Code (NEC) does not recognize voltage drop to be a safety issue, they do recommend limiting the voltage drop from the breaker box to the farthest outlet for lighting, heating and power to 3% of the circuit’s voltage. This is made possible by choosing the correct wire size. Using a voltage drop formula or voltage drop calculator can help you avoid the hassle and headache caused by choosing the wrong wiring material and sizing for your power needs.

How Much Voltage Drop is Acceptable?

The National Electrical Code says that a voltage drop of 5% at the furthest receptacle in a branch wiring circuit is passable for normal efficiency. For a 120-volt 15 ampere circuit, this means that there should be no greater than a 6 volt drop at the furthest outlet when the circuit is fully loaded.  Use our dc voltage drop calculator above to make sure you are within an acceptable range.

Voltage Drop Fundamentals

There are four fundamental causes of voltage drop, including the material used, the wire size, wire length, and current being carried. Copper is known as being a better conductor than aluminum. Larger diameter wires will have less voltage drop than smaller diameter wires that run the same length. Wire length matters since shorter wires will have less voltage drop than longer ones. Lastly, a voltage drop increases with an increase in the current flowing through the wire.

To decrease or eliminate voltage drop you can increase the size of the conductor being used to carry power to your electrical load. The increased conductor size reduces the amount of resistance on the conductor and the overall resistance on the entire circuit.

In order to choose the right wire gauge size, you’ll need to use a DC voltage drop calculator, or know the voltage drop formula.