EV charging
How long a charge takes and what it costs — Level 1, Level 2 or DC fast with a taper curve, the car's on-board charger limit, losses, flat or time-of-use prices — the range it adds per hour, the cost per mile against petrol, and the home charger circuit: 125 % breaker, wire size and receptacle under NEC 2023.
Added · updated 28 October 2026
Works with
- Dwelling service load calculation US electricalAdd to the house load puts the charger in its EVSE list as a new load
- Vehicle log Cars and EVslog each session's real kWh and cost and track mi/kWh over time
How to use it
Give the car’s usable battery, where the charge starts and stops, and the charger, and the page steps through the charge a quarter of a percent at a time: how much power the battery takes at that state of charge, how long each step takes, and what the energy drawn from the wall costs at that hour. Below it, the same charge against a petrol car, and the circuit a home charger needs.
How to use it
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Car: usable battery in kWh (the figure the maker or the community quotes as usable, a few kWh under the gross capacity), the state of charge to start from and stop at, and the car’s efficiency in mi/kWh, Wh/mi or kWh/100 km — from its trip computer, or about 3.5 mi/kWh for a mid-size car.
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Charger: Level 1 is a 120 V outlet (12 A on a 15 A circuit), Level 2 a 240 V charger (give volts and the amps it is set to, or kW), DC fast a public charger (its kW and the car’s peak DC kW). On AC, the car’s on-board charger is the limit if it is smaller — many cars take 7.2 or 11 kW, whatever the wall box offers.
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Losses: the share of the billed energy that never reaches the battery — about 15–20 % on Level 1, 8–12 % on Level 2, 5–10 % on DC. They include the charger, the car’s charger and cooling, and the battery itself.
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Price: a flat rate, or time of use with an off-peak window (it may wrap past midnight) and the hour you plug in; on DC, the price per kWh and any session fee.
The result gives the time and the clock time it finishes, the cost and the kWh billed, the range added, and the range per hour, with a chart of state of charge and power against time.
DC charging follows a typical curve: full power from about 10 % to 50 %, then falling to about half at 80 % and a tenth at 100 %. Every car has its own curve, and a cold battery charges slower; this is the shape, not your car.
Home charger circuit
For a US home, give the charger’s current (its maximum, or the lower limit it has been set to) and how it will be wired. The page gives:
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Breaker: an EV charger is a continuous load, so the branch circuit is sized at no less than 125 % of its current (NEC 2023 625.41, with 210.19(A) and 210.20(A)), rounded up to a standard size (240.6(A)). A charger set to a lower current with a restricted-access setting may go on a circuit sized for that setting (625.42).
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Wire: copper from Table 310.16 — the 75 °C column for THHN/THWN-2 in conduit with 75 °C terminals, the 60 °C column for NM-B cable (334.80); 14–10 AWG are held to 15, 20 and 30 A by 240.4(D). Where the ampacity is not a standard breaker size, the next size up is allowed (240.4(B)).
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Receptacle: a NEMA 14-50 or 6-50 on a 50 A circuit suits a 40 A charger and no more; above that the charger is hard-wired. EV charging receptacles need GFCI protection (625.54).
Before adding the circuit, check the service can carry it: the charger counts at its nameplate or 7,200 W, whichever is larger (220.57). Use the dwelling service load calculator for that, and the wire size calculator for long runs (voltage drop), aluminium, or a hot garage. Workshop circuits are in the shop power planner.
This is a planning aid, not a design. It is based on the NEC 2023; check the edition your jurisdiction has adopted and the authority having jurisdiction’s amendments. Local code and the inspector have the last word, and the charger maker’s installation instructions set the circuit it needs.
Compared with petrol
The cost per 100 miles (or km) for the EV at this charge’s price, and for a petrol car at the price and US mpg you give, and the electricity price at which they cost the same. Energy only — not servicing, tyres, insurance or the price of the car. For whole-home energy use, see the energy usage calculator; for solar, solar ROI.
Related: OBD-II diagnostics for reading a car, tyre sizes, engine calculator.
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