It’s commonly understood that the lack of electric vehicle charging stations is a significant barrier to consumer adoption. Whether you live in an apartment without a dedicated parking spot or a single-family home and need to charge quickly on longer road trips, the infrastructure availability can make or break decision-making.

But it’s less understood among even electric vehicle drivers themselves how complicated charging can be, in terms of the multiple formats and charging speeds. First, the good news: the U.S. now has 47,114 public EV charging outlets, up from 25,602 at the end of 2014, per the U.S. Department of Energy.

But here’s the problem, as E&E news covered [pay-walled]:

But they’re not all the same, and not all cars can use them all. Tesla Inc.’s Supercharger Network, for example, only works for Tesla drivers. Charging at home on a Level 1 or 2 charger can take all night; charging at a public fast-charging station can take 30 minutes or less, depending on the power provided and technology.

One of the key technology developments has been increasing the power — and speed — of the charging stations. Tesla’s Supercharger Network of 8,496 stations provides up to 120 kilowatts per car, but it is proprietary.

Other automakers have increased the capacity of their latest models, and an increasing number of stations are planning to deliver more than 100 kW, a change from the earlier 50 kW. ChargePoint Inc. has developed a 400-kW charging technology. EVgo, another charging company, is installing up to dozens of high-powered fast-charging stations of 145 to 350 kW. Automakers and technology startups have developed technology that would fully charge a car in five minutes or less, although it’s not yet widely available.

All these numbers can be confusing, and really people just want a simple answer to the question: how long will it take me to charge my battery? Here’s how I like to explain it to the average person:

• “Level 1” (or your standard wall outlet) will charge your car about 5 miles per hour. The formats are the same across all vehicles.
• “Level 2” (or 240 volts, like for a large home appliance) has more variability, but generally will give you about 20 miles per hour. The formats are also the same across all vehicles. But the variability in charging speed can be fairly significant, due to the divergent amperage (or “amps,” measuring essentially the volume of the electric current) allowed by various batteries and charging stations. Here are the three big examples of differing charging speeds just within Level 2:

1. If you can only Level 2 charge at 16 amps, that’s total power of 3.8 kilowatts (you multiply 240 volts by amps for total power). At that speed, with a Chevy Bolt EV’s 60 kilowatt-hour battery, it would take you 15.8 hours to fully charge from zero (60 divided by 3.8). With 238 mile range, that equals 15 miles per hour.
2. If the battery could accept 32 amps, that equals 7.6 kilowatts of power at the Level 2 charging station, which means the Chevy Bolt would charge fully from zero in 7.9 hours. That equals 30 miles per hour.
3. And if your battery could accept 48 amps (like all Teslas do), you could fully charge at 11.5 kilowatts in 5.2 hours, or 45 miles per hour. So 5.2 hours to 15.8 hours is a huge range, just within Level 2.

• “Fast Charge” has the most variability and also three incompatible formats across North American/European, Asian and Tesla vehicles. As the article above mentioned, most fast chargers have 50 kilowatts of power. That means you could charge your Chevy Bolt EV in a bit over an hour (60 kilowatt hours divided by 50 kilowatts), although really less than that because the car is programmed to charge at a reduced speed for the last 80% to minimize harm to the battery. So I’d bank on about two hours, or 120 miles per hour, for a full charge from zero in a 50 kilowatt fast charger. Tesla fast-chargers are much quicker at 120 kilowatts, meaning your Chevy Bolt EV (which can’t use those chargers but just for the sake of calculation) could charge closer to 30 or 40 minutes, or 200 miles in 30 minutes (although slower given the last 20% slowdown I just mentioned). And at 350 kilowatts, you could charge your Chevy Bolt EV like you are at a gas station, in perhaps just 20 minutes.

So we need more 350 kilowatt chargers, and we need them all over major interstate corridors and in urban “plazas” for apartment dwellers. We covered some solutions for this deployment in the report Plugging Away last year.

And hopefully one day charging will be so simple and ubiquitous that nobody will need to bother with all the calculations and explanations I’ve offered here.