Spec sheets for electric cars use two units that look almost the same. kW vs kWh is the difference that confuses new EV drivers most, and mixing them up leads to bad choices about batteries, chargers and running costs. At First Vehicle Leasing we explain this every week to drivers moving to electric. This guide uses current 2026 models and UK figures.
Key Takeaways
- kW (kilowatt) measures power. It tells you how fast a car can charge and how strong its motor is.
- kWh (kilowatt-hour) measures energy. It tells you how much a battery holds and what your electricity bill charges for.
- A rough guide to charging time: energy added (kWh) ÷ charging power (kW) = hours. The car's own limit and slowing above 80% make real stops longer.
- From 1 October to 31 December 2026, the Ofgem price cap averages 26.32p per kWh for electricity paid by Direct Debit, with no VAT on domestic electricity until 31 March 2027.
- Fully electric company cars are taxed at a 4% Benefit in Kind rate in 2026/27, rising to 5% in 2027/28.
What Is the Difference Between kW and kWh?
A kilowatt (kW) is a rate: how quickly energy flows. A kilowatt-hour (kWh) is an amount: how much energy has flowed or been stored. One kWh is what you get when 1 kW flows for one hour. For an EV, kW describes charging speed and motor output. kWh describes battery size and the energy you pay for.
Think of a hose filling a bucket. The width of the hose is kW, because it sets how fast water flows. The size of the bucket is kWh, because it sets how much water fits. A wider hose fills the same bucket faster. A bigger bucket takes longer to fill with the same hose, but it lasts longer once it's full.
kW = power (the hose)
Charger output, how much power the car can accept, and motor output. Higher means faster.
kWh = energy (the bucket)
Battery capacity, energy used per mile, and what you pay for on your electricity bill. Higher means more stored energy.
What Does kW Tell You About an Electric Car?
kW shows up in two places on a spec sheet: charging speed and motor power. For charging, the speed you actually get is whichever is lower, the charger's output or the most the car can accept. For motor power, kW replaces horsepower. As a rule, 1 kW is about 1.34 bhp, and 1 bhp is about 0.75 kW.
Charging speed: the lower number wins
There are two kinds of charging. AC (alternating current) charging is what you get at home and at most on-street points, and the car's onboard charger converts it for the battery. DC (direct current) rapid charging skips that step and feeds the battery directly, which is why it's so much faster. UK public chargers are grouped into four power bands, the names the Department for Transport (DfT) uses in its official charging statistics:
| Band | Power | Typical use |
|---|---|---|
| Standard | 3 kW to under 8 kW | Home wallboxes, lamp-post and overnight on-street charging |
| Standard Plus | 8 kW to under 50 kW | Car parks, supermarkets, workplaces |
| Rapid | 50 kW to under 150 kW | Retail parks and en-route stops |
| Ultra-rapid | 150 kW and above | Motorway and trunk-road hubs |
Take the new Nissan Leaf. The old hatchback, with its CHAdeMO rapid-charging plug, has been replaced by a crossover built in Sunderland. The new car uses CCS (Combined Charging System), the standard rapid-charging connector in the UK. It charges at up to 105 kW DC with the 52 kWh battery and up to 150 kW with the 75 kWh battery, and at up to 11 kW on AC. You can plug it into a 350 kW ultra-rapid charger without any harm, but it will still only draw 150 kW at most. At the other end of the scale, the Porsche Taycan can take up to 320 kW, and Porsche quotes 10–80% in 18 minutes in the best conditions.
Motor power: kW is the new bhp
The 75 kWh Leaf's motor makes 158 kW, which is about 212 bhp (158 × 1.34). The dual-motor 84 kWh Hyundai Ioniq 5 makes 239 kW, which is about 320 bhp. A more powerful motor doesn't have to use more energy on a gentle drive. How you drive matters far more.
What Does kWh Tell You About an EV Battery?
kWh is the size of the battery, the EV equivalent of fuel tank capacity. A bigger number stores more energy, so the car goes further between charges if everything else is equal. But check whether the figure is gross or usable. Carmakers keep some capacity in reserve to protect the battery, so the energy you can actually use is a little lower.
The Hyundai Ioniq 5 comes with a 63 kWh or 84 kWh battery, with official ranges of up to 354 miles. The Taycan's Performance Battery Plus is 105 kWh gross, of which about 97 kWh is usable. When you compare cars, compare usable with usable.
How Do kW and kWh Work Together to Set Charging Time?
Divide the energy you need (kWh) by the charging power (kW) and you get a rough time in hours. Charging a 75 kWh Leaf from 10% to 80% adds 52.5 kWh. On a 7 kW home wallbox that's about 7.5 hours. At a 150 kW rapid charger it would be about 21 minutes in theory, but around 30 in practice, because charging slows as the battery fills.
| Charger power | Time to add 50 kWh (theoretical) | Catch |
|---|---|---|
| 7 kW (home wallbox) | About 7 hr 10 min | Most UK homes have a single-phase supply, which tops out at around 7 kW |
| 22 kW (AC public) | About 2 hr 16 min | Only if the car's onboard charger accepts 22 kW. At 11 kW it takes about 4.5 hours |
| 50 kW (Rapid) | About 1 hour | Slows noticeably above 80% |
| 150 kW (Ultra-rapid) | About 20 min | Only if the car can accept 150 kW |
So should you pay extra for the fastest-charging car? Only if you regularly drive long distances in one go. If you charge at home overnight, you'll rarely use rapid chargers, and battery size (kWh) matters much more than peak charging speed (kW). Our guide to charging your electric car covers connectors and home installation.
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Check my eligibilityHow Much Does a kWh Cost in 2026?
Your electricity bill charges by the kWh, so this is the number that sets your running costs. From 1 October to 31 December 2026, Ofgem's cap averages 26.32p per kWh for customers on a standard variable tariff paying by Direct Debit, and there's no VAT on domestic electricity until 31 March 2027. Adding 52.5 kWh at home on that rate costs about £13.82. In August 2026, the ten biggest rapid charging networks charged between 59p and 92p per kWh on pay-as-you-go, so the same energy costs roughly £30.98 to £48.30.
Efficiency turns that into a cost per mile. It's quoted either as miles per kWh (higher is better) or kWh per 100 miles (lower is better). Official figures come from WLTP (the Worldwide Harmonised Light Vehicle Test Procedure). At 4.5 miles per kWh, home charging at 26.32p works out to about 5.85p per mile. Off-peak EV tariffs can cut that sharply.
How Do EV Taxes Work in 2026/27?
Road tax and company car tax don't depend on kW or kWh. They depend on zero emissions and the car's list price. A new electric car pays £10 of Vehicle Excise Duty (VED) in the first year and then the £200 standard rate. Company car drivers pay Benefit in Kind (BIK) at 4% in 2026/27, and a per-mile charge is planned from April 2028.
According to GOV.UK guidance on vehicle tax for electric vehicles, electric cars with a list price over £50,000 also pay the expensive car supplement, which is £440 a year in 2026/27, for five years from the second year of tax. The BVRLA has confirmed that the threshold for zero-emission cars went up from £40,000 to £50,000 from 1 April 2026. On a contract hire lease, road tax is normally included in your rental for the whole term.
BIK is worked out from the P11D value (the list price including options), not the rental. Fleet News' summary of HMRC's company car tax bands gives the example of a £40,000 electric car at 4%, which costs a basic-rate taxpayer £26.67 a month. That's why electric cars are so popular through salary sacrifice. From April 2028, Electric Vehicle Excise Duty (eVED) is planned at 3p per mile for battery electric cars. It will be run by the DVLA and was still awaiting legislation at the time of writing.
Which Battery and Charging Spec Should You Choose?
Start with your weekly mileage and where you'll charge, not the biggest numbers on the spec sheet. If you can charge at home and mostly drive locally, a smaller battery and modest charging speed will do the job and usually costs less. If you often drive long distances in one go, prioritise usable kWh first and DC kW second.
- Mostly short trips, home charging: a smaller battery is plenty. Look at the Renault 5 or the 52 kWh Leaf.
- Mixed use, occasional long trips: go for a mid-sized battery of about 60–80 kWh and a car that accepts at least 100 kW DC, such as the Kia EV3 or the 75 kWh Leaf.
- Frequent motorway miles: choose a big usable battery and fast DC charging, such as the 84 kWh Ioniq 5 or the Taycan.
- No home charging: you'll depend on public prices of 59p to 92p per kWh on the big rapid networks, so a more efficient car (higher miles per kWh) matters most.
Based on FVL's experience, drivers who charge at home rarely miss the extra charging speed they didn't pay for. Drivers who choose a battery that's too small for their routine usually regret it. Our leasing jargon buster explains any contract terms you come across.
Ready to Choose Your Next EV?
Our leasing experts at First Vehicle Leasing can help you match battery size and charging speed to the way you actually drive, then find the best value electric lease within your budget. Call us on 0333 003 3325 or browse the latest offers.
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Sources
- Vehicle tax for electric, zero and low emission vehicles - GOV.UK
- VED changes - Expensive Car Supplement for EVs - BVRLA
- What are the current benefit-in-kind (BIK) company car tax bands? - Fleet News
Written by Andy Bell, First Vehicle Leasing.
