Wire Size Calculator & Chart

Reading the Wire Size Chart (Real Talk)

Here's the thing about wire gauge: bigger numbers mean smaller wires. Backwards? Yeah. So 14 AWG is skinny, 10 AWG is fatter, and by the time you hit 4/0 you're dealing with thick cable. It's a weird system but it works.

The AWG System (and why it matters)

Every 3 gauge steps, the wire roughly doubles in area. So 12 AWG carries about twice what 18 AWG can handle. Jump from 14 to 10 and you're doubling twice over. Simple pattern once you see it.

After you hit 1 AWG, the naming gets weird: 1/0 (one-aught), 2/0, 3/0, 4/0, then kcmil sizes. Don't overthink it—just use the chart. But here's what matters in practice:

• 14-12-10-8: Learn the common branch-circuit progression. In practical residential work that usually means 15A, 20A, 30A, then larger appliance circuits.
• Copper beats aluminum at the same gauge—copper's got better conductivity, so you can go smaller and save money.
• Temperature ratings (60°C, 75°C, 90°C) are about the insulation, not the copper. Higher rating = more current capacity. Simple.

NEC Table 310.16 (The Real Rules)

These ampacity numbers come straight from the National Electrical Code. Electricians don't make them up. They assume three conductors in a conduit, normal room temperature (86°F), and nothing weird going on. If you've got 9 wires in one conduit? You're derated. Hundred-degree attic? Derated again. Plan accordingly.

• 60°C: Lower-temperature equipment and cable assemblies may force you into this column.
• 75°C: Common working column for many practical installations because terminations often control.
• 90°C: The conductor insulation may be rated here, but that does not automatically mean the connected equipment can use the 90°C ampacity.

Copper vs. Aluminum (When It Matters)

Aluminum's cheaper by the pound, but it's got higher resistance. Translation: you need it bigger. For the same 40 amps, 8 AWG copper does what 6 AWG aluminum does. That's real money difference on big feeders.

Aluminum lived in service entrances and big feeders back in the 70s-80s when copper was gold-priced. Now? Copper everywhere in residential because it's easier to work with. Big services still use aluminum sometimes—the math works better there.

What You Actually Install (Residential)

Stop overthinking it. Here's what goes in real houses:

• 15A circuits: 14 AWG (though pros usually go 12 to future-proof)
• 20A outlets/kitchen: 12 AWG (standard)
• 30A heavy loads: 10 AWG (dryer, range top)
• 40A large appliance: 8 AWG
• 50A subpanel: 6 AWG copper
• 100A service: 3 AWG copper minimum
• 200A service: 2/0 copper minimum

Why You Might Go Bigger Than The Chart Says

The NEC gives minimums. Sometimes you'll go bigger because real life gets in the way:

• Voltage drop: Long runs get voltage loss. Go bigger wire to fight it.
• Hot locations: Attic wiring in summer? Derate the wire. Go up a size or two to compensate.
• Bundled wires: More than 3 conductors together? They can't cool right. Size up.
• Continuous loads: If it runs 24/7, design for 125% of the actual current. Bigger wire.
• Future thinking: If you might add circuits later, leave headroom now.

Reference: Complete Wire Size Chart