Calculator
EV Charger Circuit Calculator
An EV charger is not sized like a normal outlet circuit, because it does not behave like one: it runs at a steady draw for hours at a stretch, not for the few minutes a table saw or a microwave pulls power. Electrical code treats anything expected to run three hours or more as a continuous load, which means the breaker has to be sized at 125% of the charger's actual draw, not simply large enough to cover it — a circuit that looks correctly sized by ordinary logic can be undersized the moment you apply the continuous-load rule that actually governs it.
This calculator works through breaker size, the minimum conductor that ampacity allows, and — separately — the voltage drop that conductor produces over your actual run length, because those are two different checks and a wire can pass the first while failing the second on a long run. None of this authorizes anyone to open a panel: a licensed electrician and a permit are not optional here, they are how the numbers below turn into a circuit that is actually safe and actually passes inspection.
Calculate your quantity
Circuit breaker
60 amps
Continuous load
59.9 amps
- Charger draw
- 47.9 amps
- Breaker's usable continuous capacity
- 48 amps
- Minimum conductor ampacity
- 65 amps
- Run length
- 60 ft
- Voltage drop
- 2.83 volts
- Voltage drop
- 1.18 %
- 6 AWG holds voltage drop to 1.18% over 60 ft, inside the 3% target.
Shopping summary
- • A 60 A two-pole breaker
- • 6 AWG copper conductors, 192 ft of wire
- • Installation and permit by a licensed electrician
This is an estimate — confirm structural work with a professional.
How this calculation works
Charger draw in amps is straightforward — kilowatts times 1,000, divided by voltage — but because the load is continuous, the breaker is sized at 125% of that draw rather than at the draw itself, then rounded up to the nearest standard breaker size. That 125% figure is not a safety margin someone chose arbitrarily; it is how continuous loads are treated under the electrical code article that governs EV charging equipment specifically.
Conductor size is picked from a standard ampacity table for 75 degree C copper, choosing the smallest gauge whose rated ampacity meets or exceeds the breaker. That satisfies code on ampacity alone — but a conductor that is legally big enough can still sag more voltage than is useful over a long run, so this page runs a second, separate check: voltage drop from the conductor's resistance, the actual current, and the run length, compared against a target percentage. When that second check fails, the conductor gets upsized again, past what ampacity alone required.
- This is planning-level math to bring to a licensed electrician, not a permit application by itself — final sizing, any required derating, and the installation itself are their work, not this page's.
- Breakers come in standard sizes only; a calculated 125% figure gets rounded up to the next one actually sold, the same way a duct or a generator size does elsewhere on this site.
- The ampacity table here assumes ordinary conditions — no more than three current-carrying conductors bundled together, moderate ambient temperature. A run through a hot attic or a crowded conduit needs a derating factor an electrician applies on top of this.
- The voltage-drop target used here is a widely followed design goal, not itself a fixed numeric maximum written into most electrical codes as a hard limit — the actual requirement is that the finished circuit performs correctly at your real run length, and this target is the number electricians commonly design toward to get there.
The formula
amps = (chargerKw x 1000) / voltage; continuousAmps = amps x 1.25; breaker = nextStock(continuousAmps); vDrop = (2 x 12.9 x amps x runLength) / conductorCmil
- amps
- The charger's actual steady current draw: rated kilowatt output times 1,000, divided by the circuit's voltage.
- continuousAmps (amps x 1.25)
- The figure the breaker is actually sized against, because a load expected to run three hours or more is classified as continuous and must be covered at 125% of its draw rather than at the draw itself.
- breaker
- The smallest standard breaker size at or above continuousAmps — standard sizes only, always rounded up, never the exact calculated figure.
- conductorCmil
- The chosen conductor's cross-sectional area in circular mils, which sets both its ampacity rating and, separately, how much voltage it drops carrying a given current over a given distance.
- vDrop
- Voltage lost along the run: 2 accounts for the round trip out and back through the circuit, 12.9 is copper's resistivity constant, amps is the real current draw, and runLength is the one-way distance — divided by the conductor's circular-mil area.
Where these numbers come from
- 125% continuous-load sizing
- Code-derived: NEC Article 625, which specifically governs electric vehicle charging equipment, treats EV charging as a continuous load and requires the circuit to be sized at 125% of the equipment's rated current — the reason this differs from an ordinary receptacle circuit sized to the load itself.
- 12/10/8/6/4/3/2/1 AWG copper ampacities (25/35/50/65/85/100/115/130 A)
- Code-derived: standard 75 degree C copper conductor ampacities, the column used for most residential terminations. Real installations can require derating below these table values depending on ambient temperature and how many current-carrying conductors share a raceway — an electrician applies that adjustment.
- 3% voltage-drop design target
- Commonly followed design guidance rather than a fixed numeric code maximum in most jurisdictions — electricians widely design branch circuits toward a 3% target (with 5% total to the farthest outlet) for equipment to perform as rated, and this page uses that convention as its default.
- 20 through 100 A standard breaker sizes
- Manufacturer-published: the amperage steps residential breakers are actually manufactured and sold in, which is why a calculated continuous-load figure always rounds up to one of these rather than landing on an arbitrary number.
Worked examples
A 7.7 kW charger, 25 feet from the panel
| Charger output | 7.7 kW (32 A) |
|---|---|
| Supply voltage | 240 |
| One-way run length | 25 ft |
| Voltage drop limit | 3 % |
| Circuit breaker | 50 amps |
|---|---|
| Continuous load | 40.1 amps |
| Charger draw | 32.1 amps |
| Breaker's usable continuous capacity | 40 amps |
| Minimum conductor ampacity | 50 amps |
| Run length | 25 ft |
| Voltage drop | 1.25 volts |
| Voltage drop | 0.52 % |
32.1 amps of charger draw becomes a 40.1 amp continuous figure at 125%, which rounds up to a 50 amp breaker — the smallest standard size that clears it. The ampacity-only conductor choice, 8 AWG rated for 50 amps, turns out to be enough on both checks here: over just 25 feet it drops only 0.52% of the circuit's voltage, well inside the 3% target.
This is the case where ampacity and voltage drop agree, and a shorter run rarely forces anything past the code-minimum conductor. The electrician's work here is still real — a permit, a load check on the panel, correct termination — but the wire size itself is not the part fighting the calculation.
An 11.5 kW charger, 200 feet from the panel
| Charger output | 11.5 kW (48 A) |
|---|---|
| Supply voltage | 240 |
| One-way run length | 200 ft |
| Voltage drop limit | 3 % |
| Circuit breaker | 60 amps |
|---|---|
| Continuous load | 59.9 amps |
| Charger draw | 47.9 amps |
| Breaker's usable continuous capacity | 48 amps |
| Minimum conductor ampacity | 65 amps |
| Run length | 200 ft |
| Voltage drop | 9.42 volts |
| Voltage drop | 3.93 % |
47.9 amps of draw still rounds to a 60 amp breaker, and ampacity alone would call for 6 AWG copper, rated for 65 amps. But over a 200 foot run, 6 AWG drops 3.93% of the circuit's voltage — over the 3% target — so the conductor gets upsized again to 4 AWG specifically to control voltage drop, not because 6 AWG was unsafe to carry the current.
This is the whole reason a two-step check exists on this page: the same breaker size, 60 amps, produced two different correct conductor answers depending on run length alone. A detached garage or a shop at the far end of a long driveway is exactly the situation where stopping at the ampacity table and skipping the drop check quietly ships a circuit that undercharges the vehicle.
Common mistakes
- Sizing the breaker to just cover the charger's steady draw instead of 125% of it. An EV charger is a continuous load by definition, and the 125% rule exists specifically for loads that run for hours, not the few minutes an ordinary appliance circuit is designed around.
- Choosing a conductor from an ampacity table and stopping there, without checking voltage drop over the actual run length — a wire that is legally big enough to carry the current can still sag enough voltage on a long run to undercharge the vehicle or trip the charger's own fault protection.
- Applying this page's ampacity figures unmodified to a run through a hot attic or a conduit already carrying several other current-carrying conductors, both of which require a derating factor below the table value that an electrician calculates for the real conditions.
- Treating the 3% voltage-drop figure as a strict numeric code maximum rather than the design target it commonly is, and assuming any number under 3% is automatically fine regardless of what the equipment manufacturer specifies for acceptable input voltage.
- Sizing the new circuit correctly in isolation without checking the panel's remaining capacity against everything already on it — a correctly sized 50 or 60 amp EV circuit can still overload a panel that has no genuine spare capacity left.
- Treating the installation as 'just a big outlet' and skipping the permit or the electrician because the charger itself plugs in. The circuit feeding it is a continuous, high-amperage addition to the panel, in the same risk category as any other major electrical work — not a plug-in appliance.
Shopping summary
Bring the breaker size, conductor size and run length from this page to a licensed electrician for a quote and a permit — that conversation, not a hardware store aisle, is where this circuit actually gets specified and installed. The labor cost calculator is a reasonable place to budget the electrician's time separately from the charger hardware itself.
If you are weighing an EV charger against other large loads on the same panel or the same backup power plan, check it against the generator size calculator — a Level 2 charger's continuous draw is large enough to be one of the bigger loads on a generator-fed panel, and a generator should never be connected by backfeeding through this or any other outlet.
Pairing EV charging with home solar is common enough to be worth sizing together: the solar array calculator can offset a charger's overnight draw if you add the charger's expected annual kWh into that page's usage figure rather than sizing the array from pre-EV utility bills alone.
FAQ
Why does the breaker need to be 125% of the charger's draw instead of just matching it?
The 125% figure isn't only a breaker rule — it flows through into conductor selection too, since this page matches wire gauge to the breaker size rather than to the charger's bare draw, so the conductor ends up sized against the continuous-load figure as well. Practically, that means skipping the 125% step doesn't just risk a breaker that runs hot and nuisance-trips under a multi-hour charge — it can also leave you with a conductor a gauge lighter than the installed breaker actually calls for.
Why did the conductor size change in the long-run example even though the breaker size didn't?
Because ampacity and voltage drop are two separate checks, and only one of them depends on distance. The breaker and the ampacity-minimum conductor are set by current alone, but voltage drop grows with run length — so the same 60 amp breaker can pair with 6 AWG on a short run and need 4 AWG on a long one, purely because the longer wire drops more voltage carrying the identical current.
Is the 3% voltage-drop figure a hard code limit I have to hit exactly?
In most jurisdictions it is a widely followed design target rather than a specific numeric maximum written into code as a strict pass/fail line. The actual requirement is that the finished circuit perform correctly and safely at your real run length — electricians commonly design toward 3% on the branch circuit as the practical way to get there, which is why this page uses it as the default.
I'm comfortable with electrical work — can I install this myself?
This page deliberately stops at the arithmetic: breaker size, conductor size, voltage drop. It does not cover panel load calculations, derating for real installation conditions, grounding, or the inspection process, all of which are exactly what a permit and a licensed electrician exist to handle correctly on a circuit this size. Treat the numbers here as what to bring to that conversation, not as a substitute for it.
Does the charger I pick change which check — ampacity or voltage drop — actually decides the conductor size?
Yes. A smaller charger on a short run is usually decided by ampacity alone, because the current is modest and voltage drop stays well under target regardless. A larger charger, a longer run, or both together shift the deciding factor to voltage drop, sometimes forcing a conductor a full size or two above what ampacity alone would require — exactly what the two worked examples above show happening.
Can I charge an EV directly from a portable generator during an outage?
Only through a properly rated connection sized for the charger's continuous draw — never by improvising a connection that bypasses the house panel or the charger's own listed input requirements. Many portable generators cannot sustain a Level 2 charger's continuous load at all; this is a case where the generator's own continuous wattage rating, not just its peak rating, is what has to cover the charger's draw for the entire session.
Where to go next
The projects this number is a step of, the guides that explain the method behind it, and the rest of its trade group.