Wire Size Calculator
Calculating Wire Size Requirements For DC Circuits
Remember that we are looking up wire sizes for two reasons:
(1) To ensure that voltage losses are within acceptable limits, and
(2) To make sure the wire doesn't get so hot that it melts the insulation (maximum ampacity).
Calculator for unbundled wire in open air, outside of engine spaces.
See below for other environments. Chart is based on USCG, ABYC, and UL standards for marine-rated (105°C dry / 75°C wet) wire.
Ampacity Limits
AWG wire size ampacity limits. However - if your wires are carrying only intermittent current, or carrying current well below the conductor's capabilities, they need not be counted in the bundle.
CM Area | AWG | Outside Engine Spaces | Inside Engine Spaces | ||||||||
# of Conductors → | 1 | 2-3 | 4-6 | 7-24 | 25+ | 1 | 2-3 | 4-6 | 7-24 | 25+ | |
1,600 | 18 | 20 | 14 | 12 | 10 | 8 | 17 | 11.9 | 10.2 | 8.5 | 6.8 |
2,600 | 16 | 25 | 17.5 | 15 | 12.5 | 10 | 21 | 14.7 | 12.6 | 10.5 | 8.4 |
4,100 | 14 | 35 | 24.5 | 21 | 17.5 | 14 | 30 | 21 | 18 | 15 | 12 |
6,500 | 12 | 45 | 31.5 | 27 | 22.5 | 18 | 38 | 26.6 | 22.8 | 19 | 15.2 |
10,500 | 10 | 60 | 42 | 36 | 30 | 24 | 51 | 35.7 | 30.6 | 25.5 | 20.4 |
16,800 | 8 | 80 | 56 | 48 | 40 | 32 | 68 | 47.6 | 40.8 | 34 | 27.2 |
26,600 | 6 | 120 | 84 | 72 | 60 | 48 | 102 | 71.4 | 61.2 | 51 | 40.8 |
42,000 | 4 | 160 | 112 | 96 | 80 | 64 | 130 | 91 | 78 | 65 | 52 |
66,500 | 2 | 210 | 147 | 126 | 105 | 84 | 178 | 124.6 | 106.8 | 89 | 71.2 |
83,690 | 1 | 245 | 171.5 | 147 | 122.5 | 98 | 208 | 145.6 | 124.8 | 104 | 83.2 |
105,600 | 1/0 | 285 | 199.5 | 171 | 142.5 | 114 | 242 | 169.4 | 145.2 | 121 | 96.8 |
133,100 | 2/0 | 330 | 231 | 198 | 165 | 132 | 280 | 196 | 168 | 140 | 112 |
167,800 | 3/0 | 385 | 269.5 | 231 | 192.5 | 154 | 327 | 228.9 | 196.2 | 163.5 | 130.8 |
211,600 | 4/0 | 445 | 311.5 | 267 | 222.5 | 178 | 378 | 264.6 | 226.8 | 189 | 151.2 |
The chart is based on an amperage capacity multiplier of:
.70 for 2-3 conductors
.60 for 4-6 conductors
.50 for 7-24 conductors
.40 for 25+ conductors
Plus a multiplier of .85 for engine room heat.
Printable Chart - Voltage Drop at 12 Volts (Double the distances for 24 volt)
12 Volts 3% Voltage drop | Feet | ||||||||||||||||||
10 | 15 | 20 | 25 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 | 110 | 120 | 130 | 140 | 150 | 160 | 170 | |
5 Amps | 18 | 16 | 14 | 12 | 12 | 10 | 10 | 10 | 8 | 8 | 8 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 |
10 Amps | 14 | 12 | 10 | 10 | 10 | 8 | 6 | 6 | 6 | 6 | 4 | 4 | 4 | 4 | 2 | 2 | 2 | 2 | 2 |
15 Amps | 12 | 10 | 10 | 8 | 8 | 6 | 6 | 6 | 4 | 4 | 2 | 2 | 2 | 2 | 2 | 1 | 1 | 1 | 1 |
20 Amps | 10 | 10 | 8 | 6 | 6 | 6 | 4 | 4 | 2 | 2 | 2 | 2 | 1 | 1 | 1 | 0 | 0 | 0 | 2/0 |
25 Amps | 10 | 8 | 6 | 6 | 6 | 4 | 4 | 2 | 2 | 2 | 1 | 1 | 0 | 0 | 0 | 2/0 | 2/0 | 2/0 | 3/0 |
30 Amps | 10 | 8 | 6 | 6 | 4 | 4 | 2 | 2 | 1 | 1 | 0 | 0 | 0 | 2/0 | 2/0 | 3/0 | 3/0 | 3/0 | 3/0 |
40 Amps | 8 | 6 | 6 | 4 | 4 | 2 | 2 | 1 | 0 | 0 | 2/0 | 2/0 | 3/0 | 3/0 | 3/0 | 4/0 | 4/0 | 4/0 | 4/0 |
50 Amps | 6 | 6 | 4 | 4 | 2 | 2 | 1 | 0 | 2/0 | 2/0 | 3/0 | 3/0 | 4/0 | 4/0 | 4/0 | ||||
60 Amps | 6 | 4 | 4 | 2 | 2 | 1 | 0 | 2/0 | 3/0 | 3/0 | 4/0 | 4/0 | 4/0 | ||||||
70 Amps | 6 | 4 | 2 | 2 | 1 | 0 | 2/0 | 3/0 | 3/0 | 4/0 | 4/0 | ||||||||
80 Amps | 6 | 4 | 2 | 2 | 1 | 0 | 3/0 | 3/0 | 4/0 | 4/0 | |||||||||
90 Amps | 4 | 2 | 2 | 1 | 0 | 2/0 | 3/0 | 4/0 | 4/0 | ||||||||||
100 Amps | 4 | 2 | 2 | 1 | 0 | 2/0 | 3/0 | 4/0 | |||||||||||
120 Amps | 2 | 2 | 1 | 0 | 2/0 | 3/0 | 4/0 | 4/0 | |||||||||||
150 Amps | 1 | 1 | 0 | 2/0 | 3/0 | 4/0 | 4/0 | ||||||||||||
200 Amps | 2/0 | 2/0 | 2/0 | 3/0 | 4/0 | 4/0 | |||||||||||||
12 Volts 10% Voltage drop | Feet | ||||||||||||||||||
10 | 15 | 20 | 25 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 | 110 | 120 | 130 | 140 | 150 | 160 | 170 | |
5 Amps | 18 | 18 | 18 | 18 | 18 | 16 | 16 | 14 | 14 | 14 | 12 | 12 | 12 | 12 | 12 | 10 | 10 | 10 | 10 |
10 Amps | 18 | 18 | 16 | 16 | 14 | 14 | 12 | 12 | 10 | 10 | 10 | 10 | 8 | 8 | 8 | 8 | 8 | 8 | 6 |
15 Amps | 18 | 16 | 14 | 14 | 12 | 12 | 10 | 10 | 8 | 8 | 8 | 8 | 8 | 6 | 6 | 6 | 6 | 6 | 6 |
20 Amps | 16 | 14 | 14 | 12 | 12 | 10 | 10 | 8 | 8 | 8 | 6 | 6 | 6 | 6 | 6 | 6 | 4 | 4 | 4 |
25 Amps | 16 | 14 | 12 | 12 | 10 | 10 | 8 | 8 | 6 | 6 | 6 | 6 | 6 | 4 | 4 | 4 | 4 | 4 | 2 |
30 Amps | 14 | 12 | 12 | 10 | 10 | 8 | 8 | 6 | 6 | 6 | 6 | 4 | 4 | 4 | 4 | 2 | 2 | 2 | 2 |
40 Amps | 12 | 12 | 10 | 10 | 8 | 8 | 6 | 6 | 6 | 4 | 4 | 4 | 2 | 2 | 2 | 2 | 2 | 2 | 2 |
50 Amps | 10 | 10 | 10 | 8 | 8 | 6 | 6 | 4 | 4 | 4 | 2 | 2 | 2 | 2 | 2 | 1 | 1 | 1 | 1 |
60 Amps | 10 | 10 | 8 | 8 | 6 | 6 | 4 | 4 | 2 | 2 | 2 | 2 | 2 | 1 | 1 | 1 | 0 | 0 | 0 |
70 Amps | 8 | 8 | 8 | 6 | 6 | 6 | 4 | 2 | 2 | 2 | 2 | 1 | 1 | 1 | 0 | 0 | 0 | 2/0 | 2/0 |
80 Amps | 8 | 8 | 8 | 6 | 6 | 4 | 4 | 2 | 2 | 2 | 1 | 1 | 0 | 0 | 0 | 2/0 | 2/0 | 2/0 | 2/0 |
90 Amps | 6 | 6 | 6 | 6 | 6 | 4 | 2 | 2 | 2 | 1 | 1 | 0 | 0 | 0 | 2/0 | 2/0 | 2/0 | 3/0 | 3/0 |
100 Amps | 6 | 6 | 6 | 6 | 4 | 4 | 2 | 2 | 1 | 1 | 0 | 0 | 0 | 2/0 | 2/0 | 2/0 | 3/0 | 3/0 | 3/0 |
120 Amps | 6 | 6 | 6 | 4 | 4 | 4 | 2 | 2 | 1 | 1 | 0 | 2/0 | 2/0 | 2/0 | 2/0 | 3/0 | 3/0 | 4/0 | 4/0 |
150 Amps | 4 | 4 | 4 | 4 | 4 | 2 | 1 | 1 | 1 | 2/0 | 2/0 | 3/0 | 3/0 | 3/0 | 4/0 | 4/0 | 4/0 | ||
200 Amps | 2 | 2 | 2 | 2 | 2 | 1 | 0 | 2/0 | 2/0 | 3/0 | 3/0 | 4/0 | 4/0 | 4/0 |
All wires should be AWG sizes (not SAE, which are smaller), with insulation rated at 105°C dry, 75°C wet. ABYC standards and USCG certifications should be met. This chart and the adjustments of temperature and bundling are only an approximation of USCG and ABYC standards. For absolute compliance, please see the applicable standards.