Voltage Drop Calculator

Calculate voltage drop in an AC or DC circuit given wire gauge, voltage, current, and length. You can also determine the correct conductor size and length for a circuit given an allowable voltage drop.

• Calculate Voltage Drop
• Calculate Minimum Conductor Size
• Calculate Max Conductor Length

Conductor Type:

CopperAluminumGoldSilverNickelSteel

Wire Gauge:

2000 kcmil1750 kcmil1500 kcmil1250 kcmil1000 kcmil900 kcmil800 kcmil750 kcmil700 kcmil600 kcmil500 kcmil400 kcmil350 kcmil300 kcmil250 kcmil0000 (4/0) AWG000 (3/0) AWG00 (2/0) AWG0 (1/0) AWG1 AWG2 AWG3 AWG4 AWG5 AWG6 AWG7 AWG8 AWG9 AWG10 AWG11 AWG12 AWG13 AWG14 AWG15 AWG16 AWG17 AWG18 AWG19 AWG20 AWG21 AWG22 AWG23 AWG24 AWG25 AWG26 AWG27 AWG28 AWG29 AWG30 AWG31 AWG32 AWG33 AWG34 AWG35 AWG36 AWG37 AWG38 AWG39 AWG40 AWG

Wire Length:

inftcmm

Phase:

AC single phaseAC 3-phaseDC

Supply Voltage:

voltskilovolts

Load Rating:

ampsmilliampswattskVA

Conductor Type:

CopperAluminumGoldSilverNickelSteel

Wire Length:

inftcmm

Phase:

AC single phaseAC 3-phaseDC

Supply Voltage:

voltskilovolts

Load Rating:

ampsmilliampswattskVA

Allowable Voltage Drop:

%

Conductor Type:

CopperAluminumGoldSilverNickelSteel

Wire Gauge:

2000 kcmil1750 kcmil1500 kcmil1250 kcmil1000 kcmil900 kcmil800 kcmil750 kcmil700 kcmil600 kcmil500 kcmil400 kcmil350 kcmil300 kcmil250 kcmil0000 (4/0) AWG000 (3/0) AWG00 (2/0) AWG0 (1/0) AWG1 AWG2 AWG3 AWG4 AWG5 AWG6 AWG7 AWG8 AWG9 AWG10 AWG11 AWG12 AWG13 AWG14 AWG15 AWG16 AWG17 AWG18 AWG19 AWG20 AWG21 AWG22 AWG23 AWG24 AWG25 AWG26 AWG27 AWG28 AWG29 AWG30 AWG31 AWG32 AWG33 AWG34 AWG35 AWG36 AWG37 AWG38 AWG39 AWG40 AWG

Phase:

AC single phaseAC 3-phaseDC

Supply Voltage:

voltskilovolts

Load Rating:

ampsmilliampswattskVA

Allowable Voltage Drop:

%

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Voltage Drop:

Voltage Drop:

In Volts:	0 volts
As a Percentage:	0%
End of Circuit Voltage:	0 volts

Conductor Diameter

inches:	0 in
millimeters:	0 mm

Conductor Cross-sectional Area

kcmil:	0 kcmil
square inches:	0 in2
square millimeters:	0 mm2

Minimum Conductor Size:

AWG

Expected Voltage Drop

 %

Maximum Conductor Length:

	feet
	meters

Learn how we calculated this below

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On this page:

• Voltage Drop Calculator
• How to Calculate Voltage Drop
• Voltage Drop Formula
• Alternate Voltage Drop Formula
• Voltage Drop Formula for Three-Phase Systems
• How to Calculate the Minimum Conductor Size
• How to Calculate the Maximum Conductor Length
• Conductor Size and Resistance Table
• References

[ see all ]

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By

Joe Sexton

Joe is the creator of Inch Calculator and has over 20 years of experience in engineering and construction. He holds several degrees and certifications.

Full bio

Reviewed by

Aditya Dua, PhD

Aditya holds a PhD in electrical engineering from Stanford University and specializes in signal processing, algorithms, and machine learning.

Full bio

and

Ahmed Sheikh, MS

Ahmed holds a Master’s degree in electrical engineering and currently works as an electrical engineer with Energy Systems Research Laboratory.

Full bio

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Cite As:

Sexton, J. (n.d.). Voltage Drop Calculator. Inch Calculator. Retrieved November 17, 2024, from https://www.inchcalculator.com/voltage-drop-calculator/

How to Calculate Voltage Drop

Voltage drop is the amount of voltage lost in a circuit due to the resistance of the conductor. Voltage drop is an important consideration when planning a circuit to allow equipment using the circuit to run as designed.

Voltage drop in a circuit means less voltage is delivered to connected devices. Electrical devices consume power, and when they get reduced voltages, the current flow increases to meet their power needs. This current increase can overheat the circuit, causing damage to the equipment and devices.

Using Ohm’s Law, the voltage can be calculated by multiplying the current by the resistance.

V_(V) = I_(A) × R_(Ω)

Ohm’s Law states that the voltage is equal to the product of the current and the resistance. You can find the resistance for various conductor sizes in the chart below, or use one of the following voltage drop formulas.

Voltage Drop Formula

Thus, you can calculate voltage drop for single-phase AC and DC circuits using the following formula derived from Ohm’s Law:^[1]

V_{drop (V)} = 2 × I_(A) × ρ_(Ω·m) × L_(m) / A_m²

Where:
V = allowable voltage drop in volts
I = current in amps
ρ = conductor resistivity in ohm-meters (Ω·m)
L = conductor length in meters
A = conductor cross-sectional area in square meters

So, the voltage drop V in volts is equal to twice the product of the current I in amps, the conductor resistivity ρ in ohm-meters, and the conductor length L in meters, divided by the cross-sectional area of the conductor A in square meters.

The resistivity of copper conductors is 1.7241 × 10^-8 Ω·m and the resistivity of aluminum conductors is 2.6548 × 10^-8 Ω·m. Since copper has lower resistivity than aluminum, the voltage drop across a copper wire would be lower than an aluminum wire, for a given length and cross-sectional area.

Alternate Voltage Drop Formula

You may also see voltage drop calculated using an alternate formula, which calculates the conductor resistance in a slightly different way:^[2]

V_{drop (V)} = I_(A) × 2 × K × L_(m) / A_mm²

Where:
V = allowable voltage drop in volts
K = direct current constant – use 12.9 for copper conductors and 21.2 for aluminum conductors. This is equal to the resistance of a conductor that is one thousand circular mils in area and one thousand feet in length.
I = current in amps
L = conductor length in meters
A = conductor cross-sectional area in square millimeters

Voltage Drop Formula for Three-Phase Systems

The formula to calculate voltage drop in three-phase systems is

V_{drop (V)} = √3 × I_(A) × ρ_(Ω·m) × L_(m) / A_m²

In a three-phase system, the voltage drop V in volts is equal to the square root of 3 times the product of the current I in amps, the conductor resistivity ρ in ohm-meters, and the conductor length L in meters, divided by the cross-sectional area of the conductor A in square meters.

How to Calculate the Minimum Conductor Size

Depending on the application, it is important to use conductors of the proper cross-sectional area for economical and reliable power delivery. A large conductor would be a waste of money, and an undersized conductor might not be able to handle the required current flows.

Using the equation for voltage drop and rearranging the variables, the minimum conductor size in square meters for a circuit can be found using the following:

A_(m²) = 2 × ρ_(Ω·m) × L_(m) × I_(A) / V_{drop (V)}

Where:
A = cross-sectional area in square meters
ρ = conductor resistivity in ohm-meters (Ω·m)
L = length in meters
I = current in amps
V_drop = allowable voltage drop in volts

The minimum cross-sectional area A for a conductor in square meters is equal to twice the product of the conductor resistivity ρ in ohm-meters, the conductor length L in meters, and the current I in amps, divided by the maximum allowable voltage drop V in volts.

You can multiply the resulting cross-sectional area by 1,000,000 to calculate the area in square millimeters. Then, use our wire size calculator to find the wire gauge with the correct cross-sectional area.

You’ll also need to consider the current rating when determining the minimum conductor size. The National Electric Code has several tables to determine the maximum allowable current for a conductor. You can also use our wire ampacity calculator to calculate the maximum current rating for a conductor.

You should always consult with an electrician or electrical professional when choosing your wire to ensure it meets the code requirements and will work safely for your application.

How to Calculate the Maximum Conductor Length

It is essential to use conductors of proper lengths to ensure minimal voltage drop in the conductive element. A longer conductor means the current must travel a longer distance through the conductive material and against more resistance.

This increase in resistance produces more voltage drops across the length of the circuit and causes it to overheat.

The maximum length of a conductor in a circuit can be determined by re-writing the formula for voltage drop like this:

L_(m) = V_{drop (V)} × A_m² / 2 × ρ_(Ω·m) × I_(A)

Where:
V_drop = allowable voltage drop in volts
I = current in amps
ρ = conductor resistivity in ohm-meters (Ω·m)
L = conductor length in meters
A = conductor cross-sectional area in square meters

The maximum conductor length is equal to the product of the maximum allowable voltage drop V_drop in volts and the cross-sectional area of the conductor in square meters, divided by twice the product of the conductor resistivity ρ in ohm-meters and the current I in amps.

Conductor Size and Resistance Table

Also check out our electricity cost calculator to see how much it will cost to power a device.