Can I interpolate between two sizes?

No. Ampacity is a tabulated heat-dissipation figure for stated conditions — an ambient of 30 °C (86 °F) and no more than three current-carrying conductors in a raceway — and a figure between two rows is one the code does not publish. The sizes also step 8, 6, 4, 3, 2, 1, so there is no 9, 7 or 5 to interpolate to.

Is 6 AWG the same as 16 mm²?

No. 6 AWG is 13.3 mm², and 16 mm² is the nearest standard metric size — larger, which is why that column reads as what to buy instead rather than as an equivalent. Check the ampacity rules that apply where the work is before substituting in either direction.

Can I use these figures for an aluminium conductor?

No — this table is copper only. Aluminium has its own column at materially lower values, and reading a copper figure for an aluminium conductor oversizes the protection, which is the dangerous direction.

Electrical

Copper conductor sizes and ampacity

Every copper conductor size this site computes with, in both systems, with the NEC ampacity beside it. AWG runs backwards and then turns over — 14 is thinner than 12, and above 1 the sizes are written 1/0 to 4/0 rather than 0 to −3 — which is the single commonest way a size is read wrong off a drawing. The area and diameter columns are not measurements: AWG is a defined geometric series, 36 AWG at 0.005 in and 4/0 at 0.46 in with a constant ratio across the 39 steps between them, so both follow by arithmetic from the gauge number alone.

15Rows, each with its source
11Calculators compute with it
CC BY 4.0Free to reuse, with credit

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Which ampacity column governs

The three ampacity columns are the same conductor at three insulation temperature ratings, and the column that governs is not the one on the cable — it is the lowest rating anywhere in the path, including the breaker and the equipment it feeds. Most breakers are listed at 75 °C and much residential equipment at 60 °C, so a 90 °C conductor very often has to be sized from the 60 °C column. The 90 °C column earns its place in derating rather than in sizing: it is the figure the adjustment and correction factors are applied to, and the result then has to land at or under the terminal's own column.

A lookup, not a formula

Ampacity is a lookup and not a formula, which is why there is no row between the ones printed. It is a tabulated heat-dissipation figure for a specific set of conditions — ambient 30 °C, not more than three current-carrying conductors in a raceway — and interpolating between two rows invents a number the code does not publish. The table also steps 8, 6, 4, 3, 2, 1, so there are no rows for 9, 7 or 5, and the sizes above 1/0 here carry geometry without an ampacity because this site's calculators stop there.

The nearest metric size

The nearest-IEC column answers what to buy instead rather than what is equivalent. A 6 AWG conductor is 13.3 mm² and the nearest standard metric size is 16 mm², which is larger — helpful when substituting, misleading if read as a conversion, and never a substitution you should make without checking the ampacity rules that apply where the work is.

The table

Every row, and where it comes from

Every row is arithmetic from a defined formula. The Nearest IEC, 60 °C, 75 °C and 90 °C columns come from a named standard, marked in their headings.

JSON

15 rows

Copper conductor sizes and ampacity. 15 rows, each stating where its figures come from.
							Source
18 AWG	0.82	1.02	0.75	—	—	—	Arithmetic
Table 310.16 publishes no ampacity for this size. The geometry is still defined, and a size the table does not carry is one the code does not let you size a branch circuit from.
16 AWG	1.31	1.29	1.5	—	—	—	Arithmetic
Table 310.16 publishes no ampacity for this size. The geometry is still defined, and a size the table does not carry is one the code does not let you size a branch circuit from.
14 AWG	2.08	1.63	2.5	15	20	25	Arithmetic
NEC 240.4(D) caps overcurrent protection on this size at 15 A regardless of the column values above — the 75 °C figure is what the conductor can carry, not what may protect it.
12 AWG	3.31	2.05	4	20	25	30	Arithmetic
NEC 240.4(D) caps overcurrent protection on this size at 20 A regardless of the column values above — the 75 °C figure is what the conductor can carry, not what may protect it.
10 AWG	5.26	2.59	6	30	35	40	Arithmetic
NEC 240.4(D) caps overcurrent protection on this size at 30 A regardless of the column values above — the 75 °C figure is what the conductor can carry, not what may protect it.
8 AWG	8.37	3.26	10	40	50	55	Arithmetic
6 AWG	13.3	4.12	16	55	65	75	Arithmetic
4 AWG	21.15	5.19	25	70	85	95	Arithmetic
3 AWG	26.67	5.83	25	85	100	115	Arithmetic
2 AWG	33.63	6.54	35	95	115	130	Arithmetic
1 AWG	42.41	7.35	35	110	130	145	Arithmetic
1/0 AWG	53.48	8.25	50	125	150	170	Arithmetic
2/0 AWG	67.43	9.27	70	—	—	—	Arithmetic
Table 310.16 publishes no ampacity for this size. The geometry is still defined, and a size the table does not carry is one the code does not let you size a branch circuit from.
3/0 AWG	85.03	10.4	95	—	—	—	Arithmetic
Table 310.16 publishes no ampacity for this size. The geometry is still defined, and a size the table does not carry is one the code does not let you size a branch circuit from.
4/0 AWG	107.22	11.68	95	—	—	—	Arithmetic
Table 310.16 publishes no ampacity for this size. The geometry is still defined, and a size the table does not carry is one the code does not let you size a branch circuit from.

Where these come from

Standard — Nearest IEC. IEC 60228 nominal conductor cross-sections. Nearest by area — not an equivalence, and never a substitution without checking the ampacity that applies where you are.
Standard — 60 °C, 75 °C and 90 °C. NFPA 70 (NEC) Table 310.16 — allowable ampacities of insulated copper conductors, ambient 30 °C, not more than three current-carrying conductors in a raceway.
Arithmetic. AWG is a defined geometric series — d = 0.005 in × 92^((36 − n)/39) — so diameter and area are arithmetic rather than measurements. The nearest IEC column is the closest of IEC 60228's nominal cross-sections, which is a comparison rather than an equivalence.

What this table does not cover

Copper only. Aluminium has its own column at materially lower values, and using a copper figure on aluminium oversizes the protection, which is the dangerous direction. No temperature correction and no conduit-fill adjustment: both are separate tables applied to the figures here, not built into them. No overcurrent device sizing beyond the 240.4(D) caps noted on the three small sizes, and nothing at all about voltage drop, which is a length problem rather than a size problem and frequently governs before ampacity does.

Behind the table

11 calculators compute with this data

Generated from the calculators themselves rather than written, grouped by trade. Open any of them to see a figure from this table at work.

Electrical

The other 4

Materials & Quantities

Equipment Grounding Conductor Sizing Reference Calculator

Cite this page

Reference data

The rest of the library

Each table here is a view onto data the calculators already compute with, and each names where its figures come from.

Every reference table Standards cited

A source on every row
A standard, a manufacturer, trade practice or arithmetic — named where the figure is.
A range where reality is one
A band prints whole, never flattened to a single figure.
Free to reuse
CC BY 4.0, and the same rows as JSON. Credit Craft Quantities.

Frequently asked questions

Which ampacity column should I read?: The one for the lowest temperature rating anywhere in the circuit — the conductor, the breaker and the equipment it feeds. Most breakers are listed at 75 °C and much residential equipment at 60 °C, so a 90 °C conductor is often sized from the 60 °C column. The 90 °C figure is where derating starts, and the derated result still has to land at or under the terminal's own column.
Can I interpolate between two sizes?: No. Ampacity is a tabulated heat-dissipation figure for stated conditions — an ambient of 30 °C (86 °F) and no more than three current-carrying conductors in a raceway — and a figure between two rows is one the code does not publish. The sizes also step 8, 6, 4, 3, 2, 1, so there is no 9, 7 or 5 to interpolate to.
Is 6 AWG the same as 16 mm²?: No. 6 AWG is 13.3 mm², and 16 mm² is the nearest standard metric size — larger, which is why that column reads as what to buy instead rather than as an equivalent. Check the ampacity rules that apply where the work is before substituting in either direction.
Can I use these figures for an aluminium conductor?: No — this table is copper only. Aluminium has its own column at materially lower values, and reading a copper figure for an aluminium conductor oversizes the protection, which is the dangerous direction.