Wire Gauge Calculator

Find the minimum conductor size (AWG/kcmil) for any electrical load per NEC §310.16. Supports 60°C, 75°C, and 90°C ratings, continuous loads (125%), and parallel runs.

NEC edition

Inputs

A

Use 75°C column for most installations — terminals are typically rated 75°C per §110.14(C)

Continuous loads must have conductors sized at 125% per §210.19

sets

#1/0 AWG minimum for parallel conductors (§310.10(H))

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⚡ Test your knowledge
NEC Article 220 was renumbered in the 2026 code cycle. What is the new article number?
  • A. Art. 100
  • B. Art. 120
  • C. Art. 200
  • D. Art. 230
💡 NEC 2026 renumbered Article 220 (Branch-Circuit, Feeder, and Service Calculations) to Article 120.
Energy Management Systems were moved from Article 750 to which article in NEC 2026?
  • A. Art. 100
  • B. Art. 125
  • C. Art. 130
  • D. Art. 150
💡 NEC 2026 moved Energy Management Systems from Article 750 to Article 130.
Which NEC standard size overcurrent device comes after 90A?
  • A. 95A
  • B. 100A
  • C. 110A
  • D. 105A
💡 Per NEC §240.6(A), the standard sizes are …90, 100, 110, 125… There is no 95A standard size.

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How it works & the NEC rules behind it

Sizing electrical conductors safely requires matching the maximum anticipated operating current (including continuous load factors) to the allowable ampacity from NEC Table 310.16 (formerly Table 310.15(B)(16)).

Critical Code Rules for Conductor Sizing:

  • The 125% Continuous Load Rule (§210.19(A)(1)): Branch-circuit and feeder conductors serving loads operating continuously for 3 hours or more (such as lighting or EV chargers) must have an allowable ampacity of not less than 125% of the continuous load plus 100% of the non-continuous load.
  • Terminal Temperature Limitations (§110.14(C)): Even if using 90°C wire (e.g. THHN/THWN-2), standard breaker terminals rated 600V or less are typically rated at 75°C. You may use the 90°C column for temperature/bundling derating calculations, but the final conductor selection cannot exceed the 75°C terminal rating!
  • Small Conductor Overcurrent Rules (§240.4(D)): Regardless of ampacity, the maximum overcurrent protection device (OCPD) size is limited: #14 Cu = 15A, #12 Cu = 20A, #10 Cu = 30A.
  • Parallel Conductors (§310.10(H)): Conductors may only be connected in parallel if they are #1/0 AWG or larger, made of identical material, length, circular mil area, insulation type, and terminated in the same manner.

Formulas & equations

Required Conductor Ampacity = (Continuous Load × 1.25) + Non-Continuous Load Parallel Ampacity per Conductor = Required Ampacity / Number of Parallel Sets
Where:
• Continuous Load: Any load expected to run continuously for 3 hours or more (§100 Definitions)
• Table 310.16 Selection: Pick the smallest conductor whose ampacity in the appropriate temperature column (usually 75°C) is ≥ Required Ampacity per Conductor.

NEC reference table

Conductor Size Copper 60°C (NM-B/UF) Copper 75°C (THWN/Terminals) Copper 90°C (THHN Derating) Aluminum 75°C
#14 AWG15 A20 A25 A—
#12 AWG20 A25 A30 A20 A
#10 AWG30 A35 A40 A30 A
#8 AWG40 A50 A55 A40 A
#6 AWG55 A65 A75 A50 A
#4 AWG70 A85 A95 A65 A
#3 AWG85 A100 A115 A75 A
#2 AWG95 A115 A130 A90 A
#1 AWG110 A130 A145 A100 A
#1/0 AWG125 A150 A170 A120 A
#2/0 AWG145 A175 A195 A135 A
#3/0 AWG165 A200 A225 A155 A
#4/0 AWG195 A230 A260 A180 A
250 kcmil215 A255 A290 A205 A
500 kcmil320 A380 A430 A310 A

*Source: NEC Table 310.16 (Allowable Ampacities of Insulated Conductors Rated Up to and Including 2000 Volts).

Worked example, step by step

Example Calculation: 48 Amp Level 2 EV Charger Conductor Sizing

Scenario: You are installing a continuous 48A hardwired EV charging station using Copper THHN conductors in conduit with standard 75°C circuit breaker terminals.

  • Step 1 (Continuous Factor): EV chargers are continuous loads per NEC Article 625. Apply 125%: 48A × 1.25 = 60 Amps minimum required conductor ampacity.
  • Step 2 (Table 310.16 Lookup): Look under the Copper 75°C column:
    • #8 Cu @ 75°C = 50A (Too small)
    • #6 Cu @ 75°C = 65A (≥ 60A → PASS)
  • Step 3 (Overcurrent Protection): 60A breaker required (§625.40 & §240.6).
  • Result: Install #6 AWG Copper THHN conductors with a 60A OCPD.

Frequently asked questions

Under NEC §110.14(C), equipment terminal ratings dictate the maximum operating temperature of the connection. Virtually all distribution panels, circuit breakers, and disconnect switches are rated for 75°C maximum (or 60°C for residential Romex/NM-B). While 90°C rated wire (like THHN) can be used as the starting point for derating adjustments, the final load cannot exceed the 75°C ampacity column.

Aluminum conductors (specifically AA-8000 series aluminum alloy) are permitted under NEC §310.106. In modern construction, aluminum is widely used for heavy feeders and services (#4 AWG through 750 kcmil) due to cost and weight savings. Aluminum is generally not permitted for 15A and 20A residential branch circuits.

For a 200A residential dwelling service under NEC Table 310.12 (formerly §310.15(B)(7)), you can use **#2/0 AWG Copper** or **#4/0 AWG Aluminum** (rated at 83% demand factor = 166A). For non-dwelling commercial 200A feeders, standard Table 310.16 requires **#3/0 AWG Copper** or **250 kcmil Aluminum**.

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