Quality electrical supplies for automotive and general use
Understanding Wire Gauge Systems
Wire gauge systems can be confusing because larger gauge numbers actually mean smaller wires! This calculator helps you convert between different systems and understand current capacity.
Wire Gauge Systems Explained
AWG (American Wire Gauge): Most common in North America. Ranges from 0000 (largest) to 40 (smallest)
SWG (Standard Wire Gauge): British Imperial standard, still used in UK for some applications
Metric (mm²): Cross-sectional area in square millimeters. Used worldwide, especially in Europe
Wire Diameter: Physical diameter of the wire in millimeters
Common Wire Gauge Conversions
AWG
Diameter (mm)
Area (mm²)
Max Current (Chassis)
Max Current (Power)
22
0.64
0.33
7A
3A
20
0.81
0.52
11A
5A
18
1.02
0.82
16A
7A
16
1.29
1.31
22A
10A
14
1.63
2.08
32A
15A
12
2.05
3.31
41A
20A
10
2.59
5.26
55A
30A
8
3.26
8.37
73A
40A
6
4.11
13.30
101A
55A
4
5.19
21.15
135A
70A
2
6.54
33.62
181A
95A
0 (1/0)
8.25
53.49
245A
125A
Current Capacity Guidelines
The maximum safe current for a wire depends on several factors:
Chassis Wiring: For short runs in open air with good cooling (e.g., car body grounds)
Power Transmission: For continuous power in bundles or conduits (more conservative)
Temperature Rating: Higher rated insulation allows more current
Installation Method: Bundled wires, conduits reduce capacity by 20-50%
Ambient Temperature: Hot environments require derating
Safety Warning: Always consult local electrical codes and use appropriate wire sizes. Undersized wires can overheat, melt insulation, and cause fires. When in doubt, go one size larger.
Voltage Drop Considerations
Voltage drop is the loss of voltage that occurs when current flows through wire resistance:
3% or less: Ideal for most applications, maintains efficiency
5%: Acceptable for non-critical loads, some performance loss
10%: Maximum for many codes, noticeable impact on performance
Automotive (12V): Even 0.5V drop is significant - use larger wire for long runs
Automotive Wire Sizing
Application
Typical Current
Recommended AWG
Signal/Control
1-3A
18-20 AWG
Lighting (LED)
3-5A
16-18 AWG
Lighting (Halogen)
10-15A
12-14 AWG
Fuel Pump
10-20A
10-12 AWG
Radiator Fan
15-25A
10-12 AWG
Alternator Output
60-100A
4-6 AWG
Starter Motor
150-300A
0-2 AWG
Battery Ground
200-400A
00-0000 AWG
Wire Selection Tips
Measure twice: Calculate both for current capacity and voltage drop
Future-proof: Go one size larger if you might add accessories
Use stranded wire: More flexible, better for automotive use
Quality matters: Use proper automotive-grade wire with appropriate insulation
Crimp properly: Poor connections create resistance and heat
Fuse everything: Wire size determines fuse size, not the other way around
Common Wiring Mistakes
Wire too small: Most common error - causes voltage drop and overheating
Poor grounds: Always use same size wire for ground as for power
Long runs ignored: Voltage drop increases with distance
Wrong fuse size: Fuse should protect the wire, not the device
Mixing wire types: Use consistent wire throughout the circuit
Wire Resistance and Calculations
Voltage Drop Formula:
Voltage Drop = (2 × Length × Resistance per meter × Current)
The "2" accounts for both positive and negative wires in the circuit.
Maximum Current Formula (simplified):
Max Current = (Voltage × Acceptable Drop %) / (2 × Length × Resistance per meter)