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The breaker caps that actually bind (NEC 240.4(D))

For the small branch circuits in houses and apartments, a separate rule dominates the table: NEC 240.4(D) caps overcurrent protection at 15 A for 14 AWG, 20 A for 12 AWG and 30 A for 10 AWG — regardless of the 75/90 °C ratings above. Read the other way, it is the fastest wire-gauge-amps answer in home wiring: lighting and receptacle circuits get 14 or 12 AWG copper, kitchen and workshop 20 A circuits get 12 AWG, and 30 A loads like water heaters and shop compressors get 10 AWG. Above 10 AWG the cap rule ends and the full table governs: 8 AWG carries 50 A breakers, 6 AWG 65 A, 4 AWG 85 A, 3 AWG 100 A, 2 AWG 115 A at 75 °C, and big feeders step up through 1/0 (150 A) to 4/0 (230 A).

What size wire for how many amps — quick answers

These copper lookups cover most questions (75 °C column, 60 °C in parentheses where folks use it):

• 15 A → 14 AWG (lighting, bedroom receptacles)
• 20 A → 12 AWG (kitchen and utility receptacles)
• 30 A → 10 AWG (dryers, water heaters, small compressors)
• 40 A → 8 AWG·60 °C / 50 A → 8 AWG at 75 °C (ranges sub-branch, spas)
• 50 A → 8 AWG at 75 °C; 6 AWG gives margin (ranges, RV pedestals)
• 60–70 A → 6 / 4 AWG; 100 A service → 4 AWG copper (or 2 AWG aluminium, per the service-size rules)
• 200 A service → 4/0 AWG copper or 250 kcmil aluminium

Aluminium answers shift one or two sizes up for the same amps — 6 AWG where copper uses 8, 2 AWG where copper uses 4 — with dedicated aluminium-rated terminations at every landing point. For DC systems the NEC does not rate anything thinner than 14 AWG, which is why our 12V wire gauge chart and automotive wire gauge chart quote free-air automotive ratings instead.

Ampacity vs voltage drop: two different limits

A wire can pass every ampacity test and still fail the job. Ampacity protects the wire from heat; voltage drop protects the load from starvation, and it grows with length. A 12 AWG run carrying 20 A is comfortable at 30 ft and lossy at 120 ft — the insulation never complains, but the far end sits several volts low, which motor compressors remember at every start.

Professional practice sizes by ampacity first, then checks voltage drop with the calculator above — its recommended size clears both limits and tells you which one forced the final gauge. For DC and marine work the drop budget is tighter still: see the round-trip resistance math on the copper wire gauge chart, where each size's Ω per 1000 ft sets the length ceiling.

Copper vs aluminium: the honest trade

The aluminium column shows the trade plainly: at the same gauge, an aluminium conductor carries roughly 60–65% of the copper rating, so it steps up one or two sizes for the same job. Its story is not capacity but cost and weight — service entrances and feeders across big spans get aluminium for a fraction of copper's price and a third of its weight, and in 2024 houses it is everywhere you do not need to bend it around a box. The engineering comes back to terminations: aluminium-rated lugs (marked AL/CU), antioxidant compound, and a serious torque habit. Plain copper keep-it-simple wins below 10 AWG, which is why branch circuits stayed copper.

What the table cannot see — the fine print

The ratings printed here assume raceway installation, three current-carrying conductors, and a 30 °C ambient room. Move the run into a hot attic (12 derating steps), bundle many circuits together, or dress ten THHN wires in one conduit and the correction factors stack: ambient + bundling can force a size up even though the chart above says fine. Continuous loads count for 125% by code; motors and welders have dedicated rules; and every final size belongs to your local code and inspector. Use this wire gauge chart amps table, the calculator and the per-gauge pages as the fast, consistent first pass — and let the licensed electrician own the last word.