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EV Basics – What’s a kilowatt hour?

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Tesla Model S dash display

So what’s a kilowatt hour or shall we ask Watts a Kilowatt hour?

As more car buyers take the plunge into owning an electric vehicle (EV), it’s important to educate on the EV specific units of measure which differ greatly than your traditional gas burning vehicle. What is a kilowatt hour? How does it differ from a kilowatt? And why does this even matter?

Background

First, let me preface everything by saying that much of what I’m about to write is based on US specific units of measure since that’s what I’m familiar with. For instance, miles vs km and US dollars versus Euros. I’m also over simplifying and breaking things down to basic laymen terms so please cut me some slack if you already know all this!

If you receive a utility bill for your residence then you should probably be somewhat familiar with, or have heard of, a kilowatt (kW) and kilowatt hours (kWh) since that’s what electricity bills are measured on. Your EV is no different and uses these same units of measure although it’s probably something you haven’t paid much attention to in the past.

kW and kWh Units

Depending on the EV display you may see watt hours (Wh) or kilowatt hours (kWh) in some places and watts (W) and kilowatts (kW) in others. The kilo or k is a standard prefix meaning a thousand. So 1 kWh is 1,000 Wh. If you own your EV long enough you may just get to the next level, megawatt hour (MWh) which would be one million Wh!

Now for the fundamental definitions:

kW is a measurement of power and kWh is a measurement of energy.

Energy is the amount of work that can be performed. kWh, calories, joules are all units of energy. A slice of pizza has 285 calories which is 0.33 Wh of energy that can be derived from that substance. Energy can be converted and change in form. For instance we can convert that slice of pizza to heat by setting it on fire. The fuel is the pizza, but don’t try converting it in your EV!

Tesla-Model-S-Dash-Energy

Power is the rate at which energy is generated or used. kW is a unit of power. When you accelerate in your EV you’re using power and when you decelerate with regenerative braking you’re generating power. The Model S dedicates half the speedometer display to the unit of power on the right side. There you can see how many kW you are using (indicator is orange) or generating (indicator is green) at any instance in time. It’s great to be able to see this however you can’t easily convert this into a cost. In order to do that, you’ll need to measure it over time and convert it into a unit of energy.

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Power is similar to your speed. 50mph is your speed, but you have to maintain that for an hour to travel 50 miles. Similarly, 40kW is how much power you’re using and you’ll have to maintain that consumption for one hour to use 40kWh. If you spend half that hour at 40kW and the other half at 20kW you’ll end up consuming 30kWh. Power usage is constantly changing and will depend on driving habit as well as usage of onboard amenities such as your seat heaters or A/C unit.

A 100W incandescent light bulb used over 1 hour will consume 100Wh of energy. If you use that 100W bulb for 8 hours every day, it will consume 800W or 0.8 kWh per day. After 30 days, it will have consumed 0.8kWh x 30 = 24 kWh. After 365 days it will have consumed 292 kWh. Measuring your EV is done in a similar fashion but keep in mind that an EV can both use and generate power (regenerative braking) over periods of time. The difference or net power used (used – generated) is what you see reported on your EV display.

Units for Charging

Charging RateCharging your EV you transfers energy back into your battery so you’re effectively storing kWh for later use. EVs report charging in different ways but the most common is to report by kW and kWh added. So a charge rate of 6 kW is storing 6kWh for every hour of charge. If you’re charging at 6kWh and charge for 2 hours you’ll have an extra 12kWh added at the end of your charge.

When it comes to driving, we’re trained to think in terms of miles, but not all miles travelled are the same when it comes to energy usage since there are variations in terrain and elevations. Weather also plays a factor for each mile travelled. A kWh stored, on the other hand, is always the same. The main difference is how you use that kWh.

The Model S offers the option to display charge rate by kW and kWh or by miles. Not surprisingly most Tesla owners choose to display charge rate in terms of miles. However it’s important to note that there’s a huge assumption being made about how many miles you can drive on a Wh and that assumption needs to account for charging efficiency. Tesla uses their proprietary algorithm to compute this value.

Tesla-Model-S-Limousine-Watts-on-Wheels

On Tesla’s online calculator they assume 300Wh/mile average use and a 90% charging efficiency. My own measurements show the average Wh/mile usage to be a bit higher (306 lifetime average) and the charging efficiency to be slightly less (81% last month).

What about Volts vs Amps?

Now you may be wondering how all this relates to volts and amps. This gets us back to the basics. One can calculate watts by multiplying volts with amps. W = V x A. So if you’re at a public charger and it’s charging at 199V and 30A (reference picture above), you’re essentially charging at 199V x 30A = 5,970W or about 6kW. This equates to 6kWh added after an hour of charging, but as we all know this is based on an ideal world where it charges at 100% efficiency with no loss. At 199V and 30A, the Model S is reporting this as a rate of 16 mi/hr.

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Lets check that math:

5,970W/300Wh/mile standard assumption = theoretical 20 miles/hr charge rate. But that doesn’t account for charging efficiency. The Model S is reporting 16 mi/hr so its assuming an 80% charging efficiency (16/20) under these conditions.

Cost

Electric Costs

Utility bills price per kWh. Your electric company may break it down by distribution vs generation, time of use, etc. and then associate a different cost per kWh on each pricing tier. It seems complex but you can simplify this.

To figure out your total cost per kWh just take your total amount of the bill and divide it by your total energy usage for the same period. That may include the various service fees, taxes, etc. but in the end you’re paying the electric company that total amount for those kWh regardless of what it’s derived from. Knowing this will help you calculate the costs for your road trips based on the kWh used.

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"Rob's passion is technology and gadgets. An engineer by profession and an executive and founder at several high tech startups Rob has a unique view on technology and some strong opinions. When he's not writing about Tesla

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Elon Musk

Tesla primes Cybercabs for 4K streaming and high bandwidth gaming with Starlink integration

Tesla is now shipping Cybercabs from Giga Texas with Starlink hardware built in as standard.

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tesla cybercab with no manual controls showing a movie with two employees inside

Tesla’s Cybercabs are now leaving Gigafactory Texas with Starlink hardware on the rear hatch in significant numbers, according to drone footage captured Tuesday by longtime Austin drone observer Joe Tegtmeyer. Production at the factory ramped back up after the Labor Day weekend, and his flyover of the outbound lot showed rows of gold Cybercabs alongside Model Y Long Wheelbase units, many carrying the satellite module for the first time as standard equipment rather than a one off retrofit.

Tesla first showed Starlink built into an actual Cybercab on August 10, when the Robotaxi account posted images of a single gold unit with the antenna integrated into the roofline above the taillights and called it the first Cybercab with Starlink integration. That followed a July reveal where Tesla and Starlink jointly posted a cutaway diagram of the antenna placement without a working vehicle to back it up. Ashok Elluswamy, Tesla’s VP of AI software, said at the time that the connection isn’t required for the car to drive itself. It exists mainly for navigation, customer service and keeping tabs on the fleet.

Musk has made a different case in public. During Tesla’s Q2 earnings call, he said the company can’t afford robotaxis stranded in what he called “Bermuda Triangles of lack of cellular connectivity,” and he separately claimed on X that Starlink will eventually reach every Tesla built, calling it the only way to deliver high bandwidth to billions of vehicles. He has also pitched the antenna as an entertainment upgrade, telling riders they would be able to stream 4K video or play games during a trip.

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The rollout has moved fast since. Robotaxi service opened to the public in Austin on September 3, and Cybercabs had already been spotted with Starlink hardware in Houston and near Miami International Airport in the weeks before Tuesday’s factory footage showed the module shipping at volume rather than on scattered test units. Whether the satellite link earns its keep is still an open question. Tesla’s unsupervised service currently runs in dense metro geofences in Texas and Florida, markets where cellular coverage is already strong, which is not where the rural dead zones Musk describes tend to show up.

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Lifestyle

Tesla Cybertruck targets job site crews with new Tailgate Utility Track and Bed Gear Box accessory

Tesla launched a $350 tailgate track and a $985 lockable Bed Gear Box for Cybertruck.

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Tesla Cybertruck construction site

Tesla’s Cybertruck team added two more items to the Tesla Shop, targeting job site crews and owners who use the truck bed for actual work rather than just showing it off. The official Cybertruck X account posted the Tailgate Utility Track and the Bed Gear Box within minutes of each other, part of a five item batch that also included a reflective jacket, a spray paint hat and an updated reflective tee.

The Tailgate Utility Track runs $350 and turns the folded down tailgate into another mounting surface. It’s a single aluminum track with a T-slot for sliding accessories and two L-track attachment points, plus two load stops included in the box. The pitch is straightforward: strap down oversized cargo, like lumber or a cooler, that hangs off the back of the bed without it sliding out mid-drive. It bolts onto the existing tailgate and works on every Cybertruck trim.

The Bed Gear Box costs $985 and is a different kind of accessory. It’s a lockable aluminum storage box, 55.78 inches long, 19.8 inches wide and 7.79 inches tall, that mounts to the bed’s L-track rails and comes with two internal bins for smaller items. According to Tesla, at just over 57 pounds empty, it’s meant to stay in place rather than come in and out with each trip, giving owners a factory-fit alternative to loose totes for tools, recovery gear or emergency supplies. Tesla’s listing notes that Long Range and Dual Motor AWD Cybertrucks need the L-Tracks accessory installed separately before the Gear Box will mount, since L-tracks come standard only on certain configurations.

Tesla Cybertruck bed gear box accessory

Tesla Cybertruck bed gear box accessory

Both accessories lean on the idea Tesla has been building toward since Elon Musk first described the Cybertruck’s third-party attachment strategy at the 2023 shareholder meeting, when he said the truck would ship with mounting points so outside companies, and Tesla itself, could keep adding gear without redesigning the bed. That’s the same L-track backbone underneath the tailgate shield and jumpseats Tesla launched last year, and the off-road armor package that arrived through the same X account in 2025.

Owners looking to round out the rest of the L-track ecosystem, cargo dividers, MOLLE panels, bed racks and similar gear, can find a wider range of options through our Cybertruck accessories collection.

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Elon Musk says he knows how to save Earth for a billion years

Elon Musk says sentient AI satellites launched from the Moon could keep Earth livable forever.

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Elon Musk spent part of his weekend describing a plan to keep the planet livable for roughly a billion years, and it starts with satellites that can think for themselves.

In a post on X, Musk argued that swapping fossil fuels for solar and wind power will not be enough to protect humanity from what he called extremely severe extinction events, the kind that occur roughly every 100 million years. His fix is what he called sentient satellites, or solar-powered satellites, controlled by AI, that would sit in a fixed spot between Earth and the Sun after being launched off the Moon using a giant electromagnetic catapult instead of rockets.

The satellites’ onboard AI would make continuous, small adjustments rather than waiting on human instructions. The mass driver is Musk’s proposed way of getting the raw material there cheaply by using an electromagnetic launch track built on the Moon, where lower gravity and no atmosphere make it far easier to fling cargo into space than it is from Earth.

Musk shared a Grok generated estimate suggesting roughly 5 percent of Florida’s land, or about 1.68 million acres, could face regular flooding by 2070 under a high sea level rise scenario, and said humanity has about 50 years to act before coastal living looks very different than it does today.

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This is not the first time Musk has floated the idea. He raised a similar concept in November, describing a solar powered AI satellite constellation that could make tiny adjustments to incoming sunlight to fine tune Earth’s temperature. Musk has also tied planetary risk to his broader vision at SpaceX, where his compensation package is explicitly linked to establishing a self-sustaining Mars colony, one he has described as an insurance policy against the kind of extinction event he referenced this weekend, and where he has said humans could set foot within five to seven years.

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