Copperline

Wire size calculator / 4 AWG ampacity

How many amps can 4 gauge wire carry?

NEC Table 310.16 listings for 4 AWG, the selected small-conductor note when this tool has one, and a Chapter 9 Table 8 voltage-drop example. Not a breaker schedule.

Four AWG is a clean label for comparing the two metals, because neither side is missing a temperature cell and neither side sits in the selected small-conductor column. Aluminum’s cells are lower and its resistance cell is higher. If you divide the two stranded resistance cells you get this row’s ratio only. The next size will not repeat that ratio, and this project does not carry a universal aluminum constant for inventing ratings.

Strand count in this Table 8 row is still in the seven-strand group used by the smaller building sizes. Area is the table’s rounded nominal square millimetres. A nearby IEC nominal size is a numerical comparison on the AWG-to-mm² page, not permission to substitute a cable or to borrow this ampacity.

The example current of 65 A does not equal any copper temperature cell for 4 AWG. The prefilled calculator uses 240 V, 100 ft one way, 75°C insulation, and 75°C terminals. Those are inputs, not a required circuit.

The selected NEC 240.4(D) column in this tool has no special ceiling for 4 AWG. A blank is not permission to omit overcurrent protection. Table ampacity, the terminal cap, and voltage drop still apply.

Aluminum 4 AWG is listed at 55 A (60°C), 65 A (75°C), and 75 A (90°C), against copper 70 A, 85 A, and 95 A. Stranded resistance at 75°C is 0.508 Ω/kft aluminum and 0.308 Ω/kft copper. The same label is not the same conductor. Some equipment permits copper only.

This chart’s Table 8 row for 4 AWG publishes stranded resistance only (0.308 Ω/kft copper, 0.508 Ω/kft aluminum). The calculator uses that stranded value.

Table 8 lists 7 strands and 41740 circular mils for 4 AWG. The rounded nominal area is 21.15 mm². Bare stranded diameter is 0.232 in, which excludes insulation and is not conduit fill.

4 AWG from NEC Table 310.16 (30°C ambient, not more than three current-carrying conductors) and Chapter 9 Table 8 at 75°C. A dash means no listing. Bare diameter excludes insulation.
ListingCopperAluminum
60°C ampacity (A)7055
75°C ampacity (A)8565
90°C ampacity (A)9575
Stranded Ω/kft0.3080.508
Solid Ω/kft——
Selected 240.4(D) ceiling (A)——
Circular mils41740
Rounded mm²21.15
Strands7
Bare diameter (in)0.232

For 4 AWG itself, not for whatever size the calculator recommends, Table 8 stranded copper resistance of 0.308 Ω/kft at 75°C gives 4.00 V (1.67% of 240 V) using 2 × I × R × L / 1,000. Reactance is omitted. Displayed volts are rounded to two decimals. The same inputs with stranded aluminum resistance 0.508 Ω/kft give 6.60 V (2.75%). If that percentage is outside the prefilled drop limit, the calculator will name a different size. That is the voltage-drop check, not a second ampacity table.

From 6 AWG to 4 AWG, the 75°C copper listing goes from 65 A to 85 A. Stranded copper resistance at 75°C goes from 0.491 Ω/kft to 0.308 Ω/kft.

From 4 AWG to 3 AWG, the 75°C copper listing goes from 85 A to 100 A. Stranded copper resistance at 75°C goes from 0.308 Ω/kft to 0.245 Ω/kft.

Planning estimate only. Consult local code and a qualified electrician before buying wire or energizing a circuit. Presets are hypothetical loads; this tool does not design motor, PV, battery, appliance, or EV installations.

Sources for these cells: existing Table 310.16 numerical cells in NFPA’s public development record, pp. 142–143 (proposed changes are not treated as adopted code) and NFPA 70 (2017), Chapter 9 Table 8, printed p. 689, in a third-party-hosted copy. The same publication supplies 110.14 (terminals and aluminum), 210.19/215.2 (continuous loads), 240.4(D) (small conductors), 250.24/250.32 (grounding), and 625.41/625.42 (EV loads). Schneider Electric’s voltage-drop formulas support the arithmetic; Table 8 AC results here omit reactance and assume unity power factor. Resistance and geometry are construction- and temperature-specific. Adopted editions and local amendments can differ.

Related guides

Open the wire size calculator · Ampacity chart · Voltage drop calculator · Printable chart

Check an example against 4 AWG

The form starts from this page’s example. The address stays on this guide until you edit a field. After an edit, a shared link includes those settings in the URL, and opening that link sends the URL to the host.

Circuit

Headline metal

Both metals are compared. Verify equipment compatibility; some equipment permits copper only.

System

General NEC notes suggest 3% on a branch or feeder and 5% combined. Special equipment and local codes may require other limits; upstream drop is not included.

Estimated size

Enter the load current and the one-way distance. The size appears here, with the limit that set it.

Temperature and bundling

These conditions affect the table ampacity used for the comparison.

Conductor insulation

Use the rating marked for wet or dry conditions. THHN is 90°C dry; XHHW is 90°C dry or 75°C wet. For NM-B use 90°C insulation and a 60°C cap below.

Terminal / cable ampacity cap

Use the lowest applicable rating at either end, including cable limits. The general unmarked default is 60°C for equipment rated ≤100 A or marked for 14–1 AWG. Confirm equipment markings before selecting 75°C; NM-B remains capped at 60°C.

Equipment grounding conductors are excluded. Verify neutrals, harmonic loads, and all other current-carrying conductors in the raceway or cable; the automatic count does not check these.

AC impedance (Chapter 9 Table 9)

At power factor 1, the reactance term is zero, but Table 9 AC resistance still applies. Unlisted sizes have no Table 9 result.

Planning estimate only. Consult local code and a qualified electrician before buying wire or energizing a circuit. Presets are hypothetical loads; this tool does not design motor, PV, battery, appliance, or EV installations.

Questions

How many amps can 4 gauge wire carry?

4 AWG copper in NEC Table 310.16 is listed at 70 A at 60°C, 85 A at 75°C, and 95 A at 90°C. Aluminum 4 AWG is listed at 55 A (60°C), 65 A (75°C), and 75 A (90°C), against copper 70 A, 85 A, and 95 A. Stranded resistance at 75°C is 0.508 Ω/kft aluminum and 0.308 Ω/kft copper. The same label is not the same conductor. Some equipment permits copper only. Those cells assume not more than three current-carrying conductors and 30°C ambient. They are not a breaker size by themselves. The selected NEC 240.4(D) column in this tool has no special ceiling for 4 AWG. A blank is not permission to omit overcurrent protection. Table ampacity, the terminal cap, and voltage drop still apply. Planning estimate only. Consult local code and a qualified electrician.

Does a hotter temperature column raise the breaker for 4 AWG?

This tool’s selected NEC 240.4(D) column has no special ceiling for 4 AWG. The blank is not permission to omit overcurrent protection, and it does not turn the 90°C cell into a breaker rating. Terminal and cable limits still cap the usable ampacity. Exceptions in the code are not checked. Planning estimate only. Consult local code and a qualified electrician.

What voltage drop does 4 AWG have on the example?

For 4 AWG itself, not for whatever size the calculator recommends, Table 8 stranded copper resistance of 0.308 Ω/kft at 75°C gives 4.00 V (1.67% of 240 V) using 2 × I × R × L / 1,000. Reactance is omitted. Displayed volts are rounded to two decimals. The same inputs with stranded aluminum resistance 0.508 Ω/kft give 6.60 V (2.75%). If that percentage is outside the prefilled drop limit, the calculator will name a different size. That is the voltage-drop check, not a second ampacity table.

Can I convert 4 AWG aluminum to copper by a fixed ratio?

No. Compare the copper and aluminum cells on this row, including resistance. The quotient of those two resistance cells is a description of this row, not a constant you can apply to other sizes or to metric cables. Equipment listings decide which metal is allowed, and torque instructions still apply.