12 Volt Wiring Reference Guide


The size of the wire you're using must be large enough to carry the maximum current expected without undue voltage losses. All wire has a certain amount of resistance to the flow of current. This resistance causes a drop in the voltage from the source to the load. Voltage drops cause inefficiencies, especially in low voltage systems (12V or less). 

The wire sizing guide below provides the minimum wire size needed to limit voltage drops to 5% at a given distance in a 12V system. If you want to limit your losses to 2% simply divide the distance by 2.5. 

AWG gauge Diameter Inches Diameter mm Ohms per 1000 ft Ohms per km Maximum amps for chassis wiring Maximum amps for power transmission
OOOO 0.46 11.684 0.049 0.16072 380 302
OOO 0.4096 10.40384 0.0618 0.202704 328 239
OO 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 0.197 0.64616 158 75
4 0.2043 5.18922 0.2485 0.81508 135 60
5 0.1819 4.62026 0.3133 1.027624 118 47
6 0.162 4.1148 0.3951 1.295928 101 37
7 0.1443 3.66522 0.4982 1.634096 89 30
8 0.1285 3.2639 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 1.26 4.1328 47 12
12 0.0808 2.05232 1.588 5.20864 41 9.3
13 0.072 1.8288 2.003 6.56984 35 7.4
14 0.0641 1.62814 2.525 8.282 32 5.9
15 0.0571 1.45034 3.184 10.44352 28 4.7
16 0.0508 1.29032 4.016 13.17248 22 3.7
17 0.0453 1.15062 5.064 16.60992 19 2.9
18 0.0403 1.02362 6.385 20.9428 16 2.3
19 0.0359 0.91186 8.051 26.40728 14 1.8
20 0.032 0.8128 10.15 33.292 11 1.5
21 0.0285 0.7239 12.8 41.984 9 1.2
22 0.0254 0.64516 16.14 52.9392 7 0.92
23 0.0226 0.57404 20.36 66.7808 4.7 0.729
24 0.0201 0.51054 25.67 84.1976 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 64.9 212.872 1.4 0.226
29 0.0113 0.28702 81.83 268.4024 1.2 0.182
30 0.01 0.254 103.2 338.496 0.86 0.142
31 0.0089 0.22606 130.1 426.728 0.7 0.113
32 0.008 0.2032 164.1 538.248 0.53 0.091
Metric 2.0 0.00787 0.200 169.39 555.61 0.51 0.088
33 0.0071 0.18034 206.9 678.632 0.43 0.072
Metric 1.8 0.00709 0.180 207.5 680.55 0.43 0.072
34 0.0063 0.16002 260.9 855.752 0.33 0.056
Metric 1.6 0.0063 0.16002 260.9 855.752 0.33 0.056
35 0.0056 0.14224 329 1079.12 0.27 0.044
Metric 1.4 .00551 .140 339 1114 0.26 0.043
36 0.005 0.127 414.8 1360 0.21 0.035
Metric 1.25 .00492 0.125 428.2 1404 0.20 0.034
37 0.0045 0.1143 523.1 1715 0.17 0.0289
Metric 1.12 .00441 0.112 533.8 1750 0.163 0.0277
38 0.004 0.1016 659.6 2163 0.13 0.0228
Metric 1 .00394 0.1000 670.2 2198 0.126 0.0225
39 0.0035 0.0889 831.8 2728 0.11 0.0175
40 0.0031 0.07874 1049 3440 0.09 0.0137
             

Voltage Drop Calculator 
by electrician.com


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.

Select Copper or Aluminum

Select American Wire Gauge (AWG) Size

Select Voltage

Enter 1-way circuit
length in feet

Enter Load
in amps

Voltage drop

Voltage at load end of circuit

Per Cent voltage drop

Wire cross section in circular mils