copper wire 1With various standards around, it is important to know how to convert proper cable sizes from one standard to another. Also, voltage drop and power losses depend on the cable length, thickness and current flowing through the cable.

Warning: no math in this article, seriously :)

AWG to mm2 Conversion Calculator

Note: Calculator DON'T accept comas ',' - instead, when needed, use dots '.'.

Enter wire size or diameter: Default value is AWG 10. Choose between AWG, inches and millimeters.
Select wire material: Select Default value is 'Wire Copper' - mostly used in cables and wires and that is usually pure electrolytic copper, but heat treated. Aluminum is not commonly found on boats and ships.
Resistivity coefficient at 20°C/68°F: Ωm Resistivity coefficient of chosen material.
Resistivity Temperature Coefficient: K-1 Resistivity coefficient depends on temperature - increase in temperature leads to increase in resistance. Even 'Resistivity Temperature Coefficient' depends on a temperature, but it is constant in this calculation.
Temperature: There is NO lower limit in calculator logic, but don't go below -20°C (253 K, -4°F), it will produce unreliable results. Above 120°C (393 K, 248F), insulation starts to melt down. If you can hold a cable with bare hand for about 5-6 seconds, then temperature of that cable is around 55-60°C (130 - 140°F).
Enter wire length: This is WIRE length - if you have two wire cable, you have to double the value of cable length. 10m wire (default value) is actually a 5m, two-wires cable.
Enter DC voltage: V DC voltage of used battery. Calculator assumes 'ideal' battery - no changes in nominal voltage with temperature and discharge current and internal resistance of the battery is assumed zero!
Enter Current: A Default value is 10A. Most of trolling motors have circuit breakers in 55-60A range.
Maximum Allowed Voltage Drop %: % Default value is 5%. This is calculated voltage drop on the cable - calculator doesn't take into account losses due to battery resistance and resistance in connectors.
   
Diameter in inches: in Diameter in inches of given wire.
Diameter in millimeters: mm Diameter in mm of given wire.
Cross sectional area in square inches: in2  
Cross sectional area in square millimeters: mm2  
Actual Resistivity Coefficient: K-1 If temperature is not 20°C/68°F, value of resistivity coefficient is corrected.
Wire resistance at 20°C/68°F: Ω Resistance of a given wire, that would be at 20°C/68°F.
Actual wire resistance: Ω If a given temperature IS 20°C/68°F, then 'Wire resistance at 20°C/68°F' and 'Actual wire resistance' are equal. If temperature is HIGHER than 20°C/68°F, then resistance increases.
Maximum Allowed Voltage Drop: V This is 5% of nominal DC voltage.
Voltage Drop at 20°C/68°F: V This is the value of voltage drop at 20°C/68°F for given wire and given current. If this value is larger than maximum allowed voltage drop, then use thicker wire.
Actuall Voltage Drop: V This is the value of voltage drop for given wire and current at given temperature. If this value is larger than maximum allowed voltage drop, then use thicker wire.
Power Loss: W Lost power in a wire - this is heat loss and leads to further increase in wire temperature and thus, increased resistance.
Power Transfered: W Power transferred from battery to the electric motor (or any other electric load).
Maximum Allowed Current at 20°C/68°F: A This is maximum current that can flow through the wire that will cause voltage drop of 5% at 20°C/68°F. If this value is lower than your desired current, then use thicker wire.
Maximum Actual Allowed Current: A This is maximum current that can flow through the wire that will cause voltage drop of 5% at given temperature. If this value is lower than your desired current, then use thicker wire.

AWG to mm2 Conversion Table

Resistivity of copper is 1.68 Ωm at 20°C. Other materials can be used as well, but most of the time, wires are made out of copper. Keep in mind that metal resistance increases with temperature, not by much, but if you can't hold your trolling motor cables in your hands due to the heat, decrease the power and get thicker cables as soon as possible.

Table columns:

- AWG #: American Wire Gauge cable thickness

- Diameter mm: diameter of cable, given in millimeters. So, if you need, for example, AWG 5 cable, but you are offered cables in millimeters only, you should buy cable 4.62mm in diameter (with 16.77 mm2 cross section area), or next thicker cable.

- Diameter inches: diameter of cable, given in inches.

- Area mm2: cross section area of the cable, given in mm2.

- Area in2: cross section area of the cable, given in inch2.

- Resistance Ω per m, Copper, t=20°C/68°F: this is resistance of ideal copper cable (of corresponding thickness), 1m in length, at 20°C/68°F. Pure copper cable has resistivity coefficient of 1.68x10-8 Ωm at 20°C/68°F and temperature coefficient of 0.003862 K-1, but copper in wires/cables is not always 100% copper. In fact, to be more manageable, even copper is annealed (kind of heat treatment) and that change resistivity coefficient at 20°C/68°F to 1.72x10-8 Ωm and temperature coefficient to 0.00393 K-1. In this table, data are provided for pure copper wire at 20°C/68°F - 1.68x10-8 Ωm and 0.003862 K-1.

Long story short - don't go cheap on wires and cables.

- Max. Current @U 5% Drop, 10m (2x5m) Wire: This is calculated maximum current trough 10m wire (2x5m cable) at given voltage, with allowed 5% drop (loss) of voltage. Keep in mind that trolling motors usually have shorter cables and they usually tolerate 5% voltage drop on cables. Even so, such cables can get very warm, even hot, if trolling motor is pushed to the limit and cable is NOT dimensioned accordingly.Bow and stern thrusters usually tolerate larger voltage drops (although, these losses should be avoided, if possible), but they usually operate for shorter period of time, when compared with electric trolling motors. Engine starters operate for few seconds only, but draw huge currents, and their cables are much thicker.

- Power Loss @U 5% Drop, 10m (2x5m) Wire: this is power loss in the cable when there is 5% voltage drop. Very thick cables are used for engine starters and they draw several hundred Amperes. Not a problem for a really thick cables. On the other hand, electric boats - having electric main motor(s) - use complex DC/AC converters/controllers and have high-voltage, multiphase motor(s), thus decreasing the currents and hence, losses in cables. Again, these are calculated values for 10m (33 feet) wire - 2x5m (2x16 feet) cable. Trolling motors usually have shorter cables. If you double the length of the cable, you should use cable that has half the resistance to keep voltage and power losses at the same level. Keep in mind that longer cable, at the same power loss, will generate less heat per meter of the cable.

- Power Transfered @U 5% Drop, 10m (2x5) Wire: this is calculated transferred power to the motor (or to anything else that is electrically powered on the boat), tolerating 5% voltage drop at given voltage.

Note: all these values are calculated having in mind ideal battery - with NO internal resistance. Internal resistance of the batteries changes with many factors and it would complicate calculations even further :)

- Voltage and Power Loss, I=60A, 10m (2x5) Wire: electric trolling motors usually have maximum current in 50-55A range and have 60A circuit breaker recommended for protection. If there is need for more power, current is kept below 60A and voltage is increased from 12V to 24, 36 or even more volts. That is why we have I=60A limit in this example. Remember, this is 10m wire or 5m cable with two wires.

I promised no formulas, so, here is the table :)

AWG
#
Diameter mm  Diameter inches Area mm2 Area in2 Resistanse
Ω per m, Copper, t=20°C/68°F
Max. Current @U 5% Drop, 10m (2x5m) Wire
Power Loss @U 5% Drop, 10m (2x5m) Wire
Power Transfered @U 5% Drop, 10m (2x5m) Wire
Voltage and Power Loss, I=60A, 10m (2x5m) Wire
6/0 14.7333 0.5800 170.4854 0.2643 98.5x10-6 @72V, 3654A @72V, 13.1kW 249kW 0.059V, 3.6W
5/0 13.1203 0.5165 135.2010 0.2096 124.3x10-6 @72V, 2896A @72V, 10.4kW 198kW 0.074V, 4.5W
4/0 11.6840 0.4600 107.2193 0.1662 156.7x10-6 @72V, 2297A @72V, 8.27kW 157kW 0.094V, 5.6W
3/0 10.4049 0.4096 85.0288 0.1318 197.6x10-6 @72A, 1821A @72V, 6.55kW 124kW 0.118V, 7.1W
2/0 9.2658 0.3648 67.4309 0.1045 249.1x10-6 @72V, 1455A @72V, 5.23kW 99.5kW 0.149V, 8.9W
0 8.2515 0.3249 53.4751 0.0829 314.2x10-6 @48V, 763A @48V, 1.83kW 34.7kW 0.188V, 11.3W
1 7.3481 0.2893 42.4077 0.0657 396.2x10-6 @48V, 605A @48V, 1.45kW 27.5kW 0.237V, 14.2W
2 6.5437 0.2576 33.6308 0.0521 499.5x10-6 @48V, 480A @48V, 1.15kW 21.8kW 0.299V, 17.9W
3 5.8273 0.2294 26.6705 0.0413  629.9x10-6 @72V, 571A
@48V, 381A
@36V, 285A
@72V, 2.05kW
@48V, 914W
@36V, 514W
@72V, 39.0kW
@48V, 17.3kW
@36V, 9.74kW
0.377V, 22.6W
4 5.1894 0.2043 21.1506 0.0328 794.3x10-6 @72V, 453A
@48V, 302A
@36V, 226A
@72V, 1.61kW
@48V, 725W
@36V, 410W
@72V, 30.9kW
@48V, 13.7kW
@36V, 7.72kW
0.476V, 28.5W
5 4.6213 0.1819 16.7732 0.0260 1.0016x10-3 @72V, 359A
@48V, 239A
@36V, 179A
@72V, 1.29kW
@48V, 575W
@36V, 323W
@72V, 24.5kW
@48V, 10.8kW
@36V, 6.12kW
0.600V, 36.0W
6 4.1154 0.1620 13.3018 0.0206 1.2630x10-3 @48V, 190A
@36V, 142A
@24V, 95A
@48V, 456W
@36V, 256W
@24V, 114W
@48V, 8.66kW
@36V, 4.85kW
@24V, 2.16kW
0.757V, 45.4W
7 3.6649 0.1443 10.5488 0.0164 1.5926x10-3 @36V, 113A
@24V, 75A
@12V, 37A
@36V, 204W
@24V, 91W
@12V, 22W
@36V, 3.86kW
@24V, 1.71kW
@12V, 421W
0.955V, 57.3W
8 3.2636 0.1285 8.3656 0.0130 2.0082x10-3 @36V, 89A
@24V, 59A
@12V, 29A
@36V, 161W
@24V, 72W
@12V, 18W
@36V, 3.04kW
@24V, 1.34kW
@12V, 330W
1.20V, 73W
9 2.9064 0.1144 6.6342 0.0103 2.5323x10-3 @36V, 71A
@24V, 47A
@12V, 23A
@36V, 128W
@24V, 57W
@12V, 14W
@36V, 2.42kW
@24V, 1.07kW
@12V, 262W
 1.51V, 91W
10 2.5882 0.1019 5.2612 0.0082 3.1932x10-3 @36V, 56A
@24V, 37A
@12V, 18A
@36V, 102W
@24V, 45W
@12V, 11W
@36V, 1.91kW
@24V, 843W
@12V, 205W
 1.91V, 115W
11 2.3048 0.0907 4.1723 0.0065 4.0266x10-3 @36V, 44A
@24V, 29A
@12V, 14A
@36V, 81W
@24V, 36W
@12V, 9W
@36V, 1.50kW
@24V, 661W
@12V, 159W
2.41V, 144W
12 2.0525 0.0808 3.3088 0.0051 5.0774x10-3 @36V, 35A
@24V, 23A
@12V, 11A
@36V, 64W
@24V, 29W
@12V, 7W
@36V, 1.19kW
@24V, 524W
@12V, 125W
3.04V, 182W
13 1.8278 0.0720 2.6240 0.0041 6.4025x10-3 @12V, 9A @12V, 6W  102W -
14 1.6277 0.0641 2.0809 0.0032 8.0734x10-3 @12V, 7A @12V, 5W  79W -
15 1.4495 0.0571 1.6502 0.0026 10.1804x10-3 @12V, 5A @12V, 4W  57W -
16 1.2908 0.0508 1.3087 0.0020 12.8372x10-3 @12V, 4A @12V, 3W  45W -
17 1.1495 0.0453 1.0378 0.0016 16.1874x10-3 @12V, 3.7A @12V, 2.2W  42W -
18 1.0237 0.0403 0.8230 0.0013 20.4120x10-3 @12V, 2.9A @12V, 1.7W  33W -
19 0.9116 0.0359 0.6527 0.0010 25.7390x10-3 - - - -
20 0.8118 0.0320 0.5176 0.0008 32.4563x10-3 - - - -
21 0.7229 0.0285 0.4105 0.0006 40.9266x10-3 - - - -
22 0.6438 0.0253 0.3255 0.0005 51.6075x10-3 - - - -
23 0.5733 0.0226 0.2582 0.0004 65.0759x10-3 - - - -
24 0.5106 0.0201 0.2047 0.0003 82.0592x10-3 - - - -
25 0.4547 0.0179 0.1624 0.0003 103.4747x10-3 - - - -
26 0.4049 0.0159 0.1288 0.0002 130.4792x10-3 - - - -
27 0.3606 0.0142 0.1021 0.0002 164.5312x10-3 - - - -
28 0.3211 0.0126 0.0810 0.0001 207.4701x10-3 - - - -
29 0.2859 0.0113 0.0642 0.0001 261.6149x10-3 - - - -
30 0.2546 0.0100 0.0509 0.0001 329.8903x10-3 - - - -
31 0.2268 0.0089 0.0404 0.0001  415.9840x10-3 - - - -
32 0.2019 0.0080 0.0320 0.0000 524.5461x10-3 - - - -
33 0.1798 0.0071 0.0254 0.0000 661.4405x10-3 - - - -
34 0.1601 0.0063 0.0201 0.0000 834.0610x10-3 - - - -
35 0.1426 0.0056 0.0160 0.0000 1.0517315 - - - -
36 0.1270 0.0050 0.0127 0.0000 1.3262090 - - - -
37 0.1131 0.0045 0.0100 0.0000 1.6723186 - - - -
38 0.1007 0.0040 0.0080 0.0000 2.1087549 - - - -
39 0.0897 0.0035 0.0063 0.0000 2.6590908 - - - -
40 0.0799 0.0031 0.0050 0.0000 3.3530516 - - - -

Cables thinner than AWG 12 should not be used on boats, IMHO, they are very thin and mechanically weak. If used, AWG 12-18 cables should be used for LED lights only. Anyway, always check manuals for any given device and if in doubt for some reason, use thicker cables.

We have really tried to verify data on this page (and not only on this page); please read our Disclaimer.

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