EV Efficiency Unit Converter

How to use this calculator

Three inputs. The range estimate is a bonus output.

Efficiency value — The number you’re starting with. Type the figure from a spec sheet, a review, or your car’s dashboard. Make sure you know which unit that number is in before selecting from the dropdown.

From unit — The unit your efficiency value is already expressed in. Five options: miles/kWh, km/kWh, kWh/100km, Wh/mile, and MPGe.

To unit — The unit you want the result in. Same five options. You can convert in any direction between any two.

Battery size (kWh) — Optional but useful. Enter the usable battery capacity of the vehicle. The calculator uses this alongside the converted efficiency to estimate real-world range in both miles and kilometres. For most EVs, usable capacity is 90–95% of the total rated capacity. A car marketed as “100 kWh” typically has 95–98 kWh usable.

The output panel shows the converted efficiency value, all equivalent representations across all five units simultaneously, and a range estimate if you entered battery size.

Why five different units exist for the same thing

EV efficiency units developed independently across different industries and regions. None of them is more “correct” than the others. They’re just different framings of energy used per unit of distance.

miles/kWh is the American framing. More miles per kWh = better. Intuitively similar to miles per gallon for petrol cars. Higher number is better.

km/kWh is the same concept in metric. More kilometres per kWh = better.

kWh/100km is the European standard. It’s consumption-first rather than distance-first. Lower number is better (you want to use less energy per 100km). This is the EV equivalent of litres/100km fuel consumption, which is the standard fuel economy metric across most of Europe and Asia.

Wh/mile (or Wh/km) is used in technical contexts, fleet management, and some dashboards. It’s granular enough to be useful per-trip. Lower is better.

MPGe (Miles Per Gallon equivalent) is an EPA-specific unit that converts electrical consumption to a “gasoline equivalent” so EVs and petrol cars can be compared on the same scale. 33.7 kWh is defined as the energy equivalent of one US gallon of gasoline.

The confusion happens because buyers read American reviews (miles/kWh or MPGe), check a European spec sheet (kWh/100km), and then compare the dashboard readout (Wh/km or Wh/mile) without realising they’re looking at three different units that all describe the same car.

The conversion formulas

All five units convert through a common base. The cleanest path runs through kWh/km as an intermediate.

The 33.7 in the MPGe formula is the EPA’s defined energy content of one US gallon of gasoline in kWh. It’s an exact defined value, not a measured approximation, so MPGe conversions are exact once you know the efficiency in miles/kWh.

The 1.60934 is the exact conversion factor between miles and kilometres (1 mile = 1.60934 km).

Full conversion table across all five units

The same efficiency expressed in all five units simultaneously. Use this to build intuition for what the numbers look like in each system.

miles/kWh	km/kWh	kWh/100km	Wh/mile	MPGe
2.0	3.22	31.07	500	67.4
2.5	4.02	24.86	400	84.3
3.0	4.83	20.72	333	101.1
3.5	5.63	17.76	286	118.0
4.0	6.44	15.53	250	134.8
4.5	7.24	13.81	222	151.7
5.0	8.05	12.43	200	168.5
5.5	8.85	11.30	182	185.4
6.0	9.66	10.36	167	202.2

Most production EVs in real-world driving land between 3.0 and 4.5 miles/kWh (15–24 kWh/100km). Hypermiling in optimal conditions can push past 5.0 miles/kWh. Heavy traffic, cold weather, and high-speed motorway driving typically drops efficiency below 3.0 miles/kWh.

Real-world examples

Comparing two EVs from different markets

A UK buyer is comparing two cars. The Volkswagen ID.4 is rated at 17.9 kWh/100km in the WLTP test. A US review of the same car reports 3.5 miles/kWh (EPA estimate). Are these the same car performing differently, or different figures for a reason?

Planning a road trip

A driver in a Tesla Model Y Long Range (75 kWh usable, 4.0 miles/kWh EPA rated) is planning a 280-mile trip. There’s a supercharger at the 190-mile mark.

Fleet manager comparing running costs

A logistics company is evaluating two EV vans. Van A: 28 kWh/100km. Van B: 22 kWh/100km. The fleet covers 80,000 km/year per vehicle. Electricity costs 0.22/kWh.

Dashboard Wh/km readout vs spec sheet kWh/100km

A driver’s dashboard shows current consumption as 187 Wh/km. The car’s WLTP spec is 16.8 kWh/100km. How does their current driving compare to the spec?

What each unit is actually useful for

Different units serve different purposes. Knowing which to reach for saves you an unnecessary conversion step.

miles/kWh or km/kWh — Best for range planning. Multiply by battery size, get range. Intuitive in the same way miles per gallon is intuitive for petrol drivers. Use these when thinking about how far you can go on a charge.

kWh/100km — Best for cost comparison and European specs. Multiply by electricity price per kWh and divide by 100, get cost per km. Used in all official European efficiency testing (WLTP). Use this when comparing running costs or reading European reviews.

Wh/mile or Wh/km — Best for granular trip analysis and fleet management. Dashboard displays in many cars use this unit because it gives per-kilometre energy figures without decimals that are easy to track in real time. Use this when tracking actual consumption on a per-trip basis.

MPGe — Best for comparing EVs to petrol cars using a familiar metric. The EPA uses it for labelling in the US. Use it when someone needs to compare an EV to a 35 MPG petrol car (an EV at 4.0 miles/kWh = 134.8 MPGe, which is meaningfully more efficient).

The unit you choose doesn't change the car's efficiency. It changes how the same information is communicated. The calculator shows all five simultaneously precisely because different people in the same conversation are often using different units without realising it.

Factors that shift your real-world efficiency

The spec sheet number is a best-case benchmark, not a guarantee. Here’s what actually moves the needle.

Speed. Aerodynamic drag increases with the square of speed. At 70 mph, drag is roughly 4 times higher than at 35 mph. Going from highway to city driving can improve efficiency by 30–50% in many EVs because regenerative braking recovers energy that would otherwise be lost as heat.

Temperature. Cold weather forces the battery management system to heat the cells, and passengers to run cabin heating (which in an EV draws directly from the battery, not waste engine heat). Efficiency can drop 20–40% in temperatures below 0°C. Heat pumps in newer EVs reduce this significantly but don’t eliminate it.

Payload and aerodynamics. Carrying 4 passengers and luggage adds 300–500 kg. A roof box increases drag substantially. Both reduce efficiency.

Driving style. Hard acceleration is the single largest controllable variable. An EV accelerated briskly to 60 mph then braked to a stop uses far more energy than one that accelerated gently and slowed with regenerative braking. The difference between aggressive and smooth driving on the same route can be 25–35%.

Regenerative braking settings. High regen modes recover more energy on deceleration. In city driving with frequent stops, high regen can claw back 15–25% of the energy that would otherwise be lost.

The bottom line

Five units. One underlying measurement. The calculator converts between all of them instantly and adds a range estimate when you enter battery size.

The unit that matters depends on what you’re doing. Range planning: miles/kWh or km/kWh. Cost comparison: kWh/100km. Dashboard monitoring: Wh/km or Wh/mile. US spec comparison: MPGe.

Real-world efficiency is always lower than the rated figure. How much lower depends on temperature, speed, and driving style more than almost any other factor. Use the rated efficiency for comparisons between vehicles. Use a 75–85% factor on that number for actual trip planning.