Voltage drop calculator


The following calculator calculates the voltage drop, and voltage at the end of the wire for American Wire Gauge from 4/0 AWG to 30 AWG, aluminum or copper wire. (Note: It just calculates the voltage drop, consult the above table for rules-of-thumb, or your local or national electrical code or your electrician to decide what is legal!) Note that the voltage drop does not depend on the input voltage, just on the resistance of the wire and the load in amps.

Select Copper or Aluminum

Select American Wire Gauge (AWG) Size

Select Voltage

Enter 1-way circuit
length in feet (the calculation is for the round trip distance)

Enter Load
in amps


Voltage drop

Voltage at load end of circuit

Per Cent voltage drop

Wire cross section in circular mils

 

AWG: In the American Wire Gauge (AWG),also known as the Brown & Sharpe wire gauge, is a standardized wire gauge system used since 1857 predominantly in North America for the diameters of round, solid, nonferrous, electrically conducting wire. Dimensions of the wires are given in ASTM standard B 258. The cross-sectional area of each gauge is an important factor for determining its current-carrying capacity. Diameters can be calculated by applying the formula D(AWG)=.005·92((36-AWG)/39) inch. For the 00, 000, 0000 etc. gauges you use -1, -2, -3, which makes more sense mathematically than "double nought." This means that in American wire gage every 6 gauge decrease gives a doubling of the wire diameter, and every 3 gauge decrease doubles the wire cross sectional area. Similar to dB in signal and power levels. An approximate but accurate enough form of this formula contributed by Mario Rodriguez is D = .460 * (57/64)(awg +3) or D = .460 * (0.890625)(awg +3).

American wire gauge.jpg

Metric Wire Gauges (see table below)

Metric Gauge: In the Metric Gauge scale, the gauge is 10 times the diameter in millimeters, so a 50 gauge metric wire would be 5 mm in diameter. Note that in AWG the diameter goes up as the gauge goes down, but for metric gauges it is the opposite. Probably because of this confusion, most of the time metric sized wire is specified in millimeters rather than metric gauges.

Load Carrying Capacities (see table below)

Definition: ampacity is the current carrying capability of a wire. In other words, how many amps can it transmit? The following chart is a guideline of ampacity or copper wire current carrying capacity following the Handbook of Electronic Tables and Formulas for American Wire Gauge. As you might guess, the rated ampacities are just a rule of thumb. In careful engineering the voltage drop, insulation temperature limit, thickness, thermal conductivity, and air convection and temperature should all be taken into account. The Maximum Amps for Power Transmission uses the 700 circular mils per amp rule, which is very very conservative. The Maximum Amps for Chassis Wiring is also a conservative rating, but is meant for wiring in air, and not in a bundle. For short lengths of wire, such as is used in battery packs you should trade off the resistance and load with size, weight, and flexibility. NOTE: For installations that need to conform to the National Electrical Code, you must use their guidelines. Contact your local electrician to find out what is legal!

 

AWG Gauge

Diameter

(Inches)

Diameter

(mm)

Ohms per 1000

(@ T=20oC)

Ohms per km

(@ T=20oC)

Max amps for chassis wiring

Max amps for power X-mission

0000

0.4600

11.6840

0.0490

0.160720

380

302

000

0.4096

10.40384

0.0618

0.202704

328

239

00

0.3648

9.26592

0.0779

0.255512

283

190

0

0.3249

8.25246

0.0983

0.322424

245

150

1

0.2893

7.34822

0.1239

0.406392

211

119

2

0.2576

6.54304

0.1563

0.512664

181

94

3

0.2294

5.82676

0.1970

0.646160

158

75

4

0.2043

5.18922

0.2485

0.815080

135

60

5

0.1819

4.62026

0.3133

1.027624

118

47

6

0.1620

4.11480

0.3951

1.295928

101

37

7

0.1443

3.66522

0.4982

1.634096

89

30

8

0.1285

3.26390

0.6282

2.060496

73

24

9

0.1144

2.90576

0.7921

2.598088

64

19

10

0.1019

2.58826

0.9989

3.276392

55

15

11

0.0907

2.30378

1.2600

4.132800

47

12

12

0.0808

2.05232

1.5880

5.208640

41

9.3

13

0.0720

1.82880

2.0030

6.569840

35

7.4

14

0.0641

1.62814

2.5250

8.282000

32

5.9

15

0.0571

1.45034

3.1840

10.44352

28

4.7

16

0.0508

1.29032

4.0160

13.17248

22

3.7

17

0.0453

1.15062

5.0640

16.60992

19

2.9

18

0.0403

1.02362

6.3850

20.94280

16

2.3

19

0.0359

0.91186

8.0510

26.40728

14

1.8

20

0.0320

0.81280

10.150

33.29200

11

1.5

21

0.0285

0.72390

12.800

41.98400

9

1.2

22

0.0254

0.64516

16.140

52.93920

7

0.92

23

0.0226

0.57404

20.36

66.78080

4.7

0.729

24

0.0201

0.51054

25.67

84.19760

3.5

0.577

25

0.0179

0.45466

32.37

106.1736

2.7

0.457

26

0.0159

0.40386

40.81

133.8568

2.2

0.361

27

0.0142

0.36068

51.47

168.8216

1.7

0.288

28

0.0126

0.32004

64.9

212.8720

1.4

0.226

29

0.0113

0.28702

81.83

268.4024

1.2

0.182

30

0.0100

0.254

103.2

338.4960

0.86

0.142

31

0.0089

0.22606

130.1

426.7280

0.700

0.1130

32

0.0080

0.2032

164.1

538.2480

0.530

0.0910

Metric 2.0

0.00787

0.200

169.4

555.6100

0.510

0.0880

33

0.00710

0.18034

206.9

678.6320

0.430

0.0720

Metric 1.8

0.00709

0.18000

207.5

680.5500

0.430

0.0720

34

0.00630

0.16002

260.9

855.7520

0.330

0.0560

Metric 1.6

0.00630

0.16002

260.9

855.7520

0.330

0.0560

35

0.00560

0.14224

329.0

1079.120

0.270

0.0440

Metric 1.4

0.00551

0.14000

339.0

1114

0.260

0.0430

36

0.00500

0.12700

414.8

1360

0.210

0.0350

Metric 1.25

0.00492

0.12500

428.2

1404

0.200

0.0340

37

0.00450

0.11430

523.1

1715

0.170

0.0289

Metric 1.12

0.00441

0.11200

533.8

1750

0.163

0.0277

38

0.00400

0.10160

659.6

2163

0.130

0.0228

Metric 1

0.00394

0.10000

670.2

2198

0.126

0.0225

39

0.00350

0.08890

831.8

2728

0.110

0.0175

40

0.00310

0.07874

1049

3442

0.090

0.0137

 

This chart of American Wire Gauge (AWG) wire sizes and rated ampacities is data intended for the pleasure of our readers only. Typographical errors, etc. are probable. Please point out errors. The data listed are incomplete and should be used as a guideline only. Please contact manufacturers for the latest data.