kW, kWh and Amps Explained Simply
📅 Published on 1 August 2026
These three terms often get mixed up, but they mean different things: kilowatt (kW) is a power rating - how fast energy flows, roughly comparable to the diameter of a water pipe. Kilowatt-hour (kWh) is an amount of energy - how much flows in total, comparable to the amount of water running through the pipe. Amp (A) is the electrical current, which together with voltage (volts) gives you power in kW.
For the battery, what ultimately counts is kWh: a 60 kWh battery theoretically needs about an hour to fully charge at 60 kW charging power (longer in practice, since the charging curve flattens out toward the end). Higher kW numbers mean faster charging, but only if both the car and the charging station actually support that power - the lower of the two limits decides.
AC charging (alternating current, usually at home or at a wallbox) is capped at 11 or 22 kW because the vehicle has to convert the power to direct current itself. DC fast charging (direct current, at public fast chargers) skips that conversion step and can therefore reach 50 kW up to well over 350 kW. Elunio shows each station's charging power in kW - the single most important value for estimating charging time and planning stops correctly.
The water-pipe analogy taken further: pressure, flow rate, and total volume
Once you're comfortable with the basic distinction between kW and kWh, it helps to push the water-pipe picture one step further, because it also explains where amps and volts fit in. Voltage is like water pressure - the force pushing electricity through the wire. Current, measured in amps, is like the flow rate - how much water actually moves through the pipe per second at that pressure. Multiply pressure by flow rate and you get power, which in electrical terms is roughly kW = volts × amps ÷ 1000. That's why a charger's rated kW output depends on both numbers together, not on amps alone: a system running at a higher voltage can deliver more power at the same current than one running at a lower voltage, which is part of why DC fast chargers use much higher voltages than a household AC socket.
Kilowatt-hours, then, are simply that flow rate sustained over time - the total volume of water that has passed through the pipe by the time you turn off the tap. A 22 kW charger running for exactly one hour delivers 22 kWh, the same way a hose running at a fixed rate for an hour fills a fixed-size bucket. This is also why charging speed and charging duration are two completely separate questions: a fast charger lets you fill the same bucket in less time, but the bucket itself - your battery's usable capacity in kWh - never changes based on how quickly you fill it.
Why your home electrical panel limits how fast you can charge
Before choosing a home wallbox, it's worth understanding that your house's own electrical panel sets a hard ceiling on what's possible, independent of what any charger manufacturer advertises. Most residential panels are rated for a total current draw of somewhere between 40 and 100 amps, shared across everything running in the house at once - lighting, heating, kitchen appliances, and now potentially an EV charger too. An electrician sizing a wallbox installation has to account for this shared capacity, not just the charger's maximum rating in isolation.
This is exactly why many modern wallboxes include dynamic load management: a feature that automatically reduces the charging current whenever the rest of the house draws more power, so the total never exceeds what the panel and the incoming supply cable can safely handle. Without this kind of safeguard, running an oven, a washing machine, and a full-power EV charger simultaneously could overload an older panel. If you're planning a home installation, ask your electrician directly what your panel can spare for charging, since that number - not the wallbox's theoretical maximum - is often the real limiting factor.
Single-phase vs three-phase AC charging explained
Most homes in much of Europe are wired with a single-phase supply for standard sockets, which caps AC charging at around 7.4 kW even with a capable wallbox, since a single 230-volt phase can only carry so much current safely. Homes and buildings with a three-phase connection - common in many countries for larger properties or newer installations - can spread the load across three separate phases simultaneously, which is what unlocks the higher 11 kW and 22 kW AC charging tiers you'll see advertised on wallbox spec sheets.
Having three-phase power available at your property is only half the equation, though: your car's onboard charger, the component that converts incoming AC to DC for the battery, also has to support three-phase input. Many electric vehicles, even relatively new ones, ship with an onboard charger capped at 11 kW regardless of how much power the wallbox itself could theoretically supply, simply because a higher-capacity onboard charger adds cost and weight that not every manufacturer builds in as standard. Checking your specific vehicle's onboard charger rating before investing in a 22 kW wallbox can save you from paying for capacity you'll never actually use.
Reading a charging station's spec sheet without getting confused
The kW figure printed on a charging station or listed in an app is almost always a maximum, not a guarantee, and real-world sessions frequently run below that ceiling for entirely normal reasons. Charging power tapers as the battery fills, following what's usually called the charging curve: most batteries accept power fastest somewhere in the 20-60% state-of-charge range and then taper off noticeably as they approach full, which is simply how lithium-ion chemistry protects itself from being pushed too hard near capacity.
Ambient and battery temperature play a role too - a cold battery on a winter morning will often charge more slowly than the same battery on a warm afternoon, since the battery management system deliberately limits current until the cells warm up to their optimal operating range. None of this means the spec sheet is wrong; it simply means the advertised number describes a best-case peak rather than what you should expect for an entire session, which is exactly why real average charging speed usually comes in noticeably below the headline figure.
Estimating charging time from kW and kWh without a calculator
A rough but genuinely useful rule of thumb: divide the kWh you need by the average kW you expect to receive, not the peak figure printed on the charger, since the average across a full session is typically lower once the charging curve is factored in. Needing 30 kWh at an average of 50 kW works out to roughly 36 minutes, while the same 30 kWh at an average of 20 kW takes closer to an hour and a half - the gap between average and peak power is often the single biggest source of surprise on longer trips.
On DC fast chargers specifically, it's usually more time-efficient to stop charging around 80% rather than pushing to 100%, precisely because that final stretch is where the charging curve tapers hardest and each additional percentage point takes disproportionately longer to add. Elunio's own charging time estimate deliberately keeps things simple and calculates with one flat power figure across the whole session (the lower of station and vehicle limits) rather than modeling the actual curve, so the displayed minutes are a rough guide, and real sessions pushed close to 100% typically take longer in practice than the estimate suggests. That's exactly why the 80% rule of thumb pays off in practice when planning multiple stops on a route.
Why battery size in kWh doesn't tell the whole story about range
Two vehicles with an identical 60 kWh battery can deliver noticeably different real-world ranges, because the number that actually determines range is efficiency - how many kWh the car consumes per 100 km driven, sometimes expressed instead as Wh per km. A lighter, more aerodynamic vehicle can travel considerably further on the same 60 kWh than a heavier one with a less efficient drivetrain or a boxier shape that fights more wind resistance at speed.
Efficiency also swings substantially with conditions: cold weather can increase consumption meaningfully due to battery heating and cabin heating demands, while steady highway speeds above roughly 110-120 km/h tend to consume noticeably more energy per km than city driving thanks to aerodynamic drag rising sharply with speed. Rather than relying purely on a manufacturer's official WLTP or EPA figure, it's worth checking your own vehicle's real-world efficiency after a few weeks of ownership, since that personal number is what should actually drive your charging stop planning.
Does a higher amp rating always mean faster charging?
Not necessarily - amps alone don't determine power, because voltage and the number of phases both factor into the calculation too. A wallbox delivering 32 amps on a single phase produces roughly 7.4 kW, while a different wallbox delivering just 16 amps but spread across three phases produces roughly 11 kW - meaningfully more power despite the lower amp figure, simply because three-phase multiplies the effective throughput. Whenever you're comparing two chargers, the kW rating is the number that actually matters for charging speed, while the amp rating on its own can be genuinely misleading without knowing the voltage and phase configuration behind it.
Why does my car charge slower than the station's maximum kW rating?
The most common reason is simply that your vehicle's onboard charger or DC charging capability has a lower ceiling than the station itself - plugging a car with an 11 kW onboard charger into a 22 kW AC wallbox will still only draw 11 kW, since the lower of the two limits always decides. On DC fast chargers, the vehicle's own battery management system additionally throttles the incoming power based on state of charge, cell temperature, and how full the battery already is, all independent of what the charger is technically capable of delivering. If a car repeatedly charges well below a station's advertised maximum, checking the vehicle's own peak charging spec and typical charging curve - both usually published by the manufacturer - is a better diagnostic step than assuming the charging station itself is underperforming.
Once these distinctions between kW, kWh, amps, and phases feel intuitive, comparing charging stations, sizing a home wallbox correctly, and estimating charging stop times on a longer trip all become far more straightforward exercises rather than guesswork. It's a small amount of upfront learning that pays off every single time you plan a route or evaluate whether a new charger is actually worth using.
Sources: Fraunhofer-Institut für System- und Innovationsforschung (ISI) · VDE Verband der Elektrotechnik, Elektronik, Informationstechnik e.V.