SettingsSettings for this calculationUS
The charger's rated continuous current draw, from its nameplate or manual.
Common Level 2 home chargers are rated 16A, 24A, 32A, 40A, or 48A continuous — check your specific unit, since setting it lower than its max via the charger's own configuration is common.
Minimum breaker size
40 A breaker
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
They open the calculator with your figures already in it
EV Charger Circuit Calculator: 40 A breaker — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- 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
Inputs used
- Charger Continuous Amp Rating
- 32
Intermediate steps
- Minimum required (125% rule)
- 40 A
Confidence note: 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.
What this calculation does not cover
- SIZES THE BREAKER, NOT THE SERVICE. The question that stops most EV installations is whether the existing service and panel can carry another continuous load of this size at all, and that is a whole-dwelling load calculation under the code's demand rules — not something a charger's own rating can answer. A panel with a spare double-pole space is not the same as a service with spare capacity.
- Where the service is short, load management is often the answer rather than an upgrade: a listed energy management system, or a charger that sheds when the range is on, lets the circuit be sized to what is actually available. Both are code-recognised and both are far cheaper than a new supply.
- The conductor is a separate calculation. Ampacity at the breaker size, derating for ambient temperature and for conductors sharing a raceway, the termination temperature rating, and voltage drop over what is often a long garage or driveway run all have to be satisfied — a correctly sized breaker on a conductor that fails any of those is the dangerous combination.
- Says nothing about the ground-fault protection, disconnecting means, or outdoor and wet-location requirements that apply to the equipment itself and vary with where it is mounted.
- A receptacle-connected charger and a hardwired one are treated differently by the code, and the choice affects both the protection required and whether the charger may be at the full 125% figure at all.
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.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations2
- 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
Which documents these citations point at
- National Electrical Code (NFPA 70) — 210.19(A)(1) (United States)Electrical installations — conductor sizing and protection, load calculation, wiring methods, grounding and working clearances.
A code or standard has force only where a jurisdiction has adopted it, usually with local amendments. This site holds no adoption data for any authority, so check what is in force with the authority where you build. Any section cited above without an edition should be checked against the edition in force where you build. What it would take to know.
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Your workspace
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Protection this work requires
- Stop and check first. Textured ceiling coatings, board behind panels, floor tiles and bitumen adhesive in older buildings — built before asbestos was banned or phased out where you are — can contain asbestos, and drilling or sanding them releases fibres. Do not disturb it — have it sampled first. This is not a job for better PPE.
Tools and safety for this job
To first-fix electrical. Generic types, no brands, no prices.
- Assume every cable is live until proved dead at the point you will touch, with a two-pole tester you have just proved on a known source.
First-fix electrical: This site does not publish a tool list for electrical installation work. In every market it serves, fixed wiring is either reserved to a registered electrician or notifiable to a building authority, and the failure mode is a fire or an electrocution months later rather than a visibly bad job on the day. The calculator gives you the quantities to discuss and to buy against. The installation is a job for a qualified electrician, and the certificate they issue is the point of them.