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EV Charger Circuit Calculator

Find the minimum breaker size for a Level 2 EV charger circuit, based on the NEC's 125% continuous-load rule.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-25 · v1.0.0

Market
Imperial · sales tax

Minimum breaker size

40 A breaker

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The breaker size also requires correctly-sized wiring for that circuit (see the Wire Gauge Voltage Drop Calculator) — always have the final circuit installed or verified by a licensed electrician and permitted per local code.

Minimum required (125% rule)
40 A

At the values currently entered, the minimum breaker size works out to 40 A breaker. Confidence is moderate: the method is sound, but real materials and site conditions vary. Figures are shown for United States, where IRC 2024 is the governing residential reference; switch the market above if you are building elsewhere.

Add the equipment this sizes

This result is a specification — 40 A breaker — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • NEC 210.19(A)(1) and 210.20(A): EV charging is a continuous load (runs 3+ hours), so the circuit must be sized at 125% of the charger's rated continuous amps
  • Standard residential breaker sizes: 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 125, 150 A

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Frequently asked questions

Why 125% instead of matching the breaker exactly to the charger's amps?
The NEC requires continuous loads (anything running 3+ hours, which describes most EV charging sessions) to use only 80% of a breaker's rating — equivalently, sizing the breaker at 125% of the load, which is what this calculator does.
Can I just install a bigger breaker to charge faster?
No — the breaker size must match both the charger's rating and the wire gauge feeding it. Oversizing the breaker beyond what the wire safely carries is a fire hazard, not a way to increase charging speed.
Does this replace an electrician's assessment?
No. This estimates the minimum circuit requirement for the charger itself — a licensed electrician still needs to confirm your panel has available capacity and that the full circuit (wire, conduit run, disconnect if required) meets local code before installation.