To fully charge an electric car, you need roughly its battery size in kWh plus 10 to 15% for charging losses. A 40 kWh battery takes about 45 to 47 units from your electricity meter. At ₹8 per unit, that’s around ₹360 to ₹380 for a full charge from near empty.
When people in India shop for a petrol car, the first question is “mileage kitna hai?” With an EV, the question changes to: how many units does it take, and what does that do to my electricity bill?
The answer turns out to be simpler than most people expect. And cheaper.
How many units does it take to fully charge an electric car?
One unit on your electricity bill is one kWh. So the battery size in kWh tells you most of what you need. The rest is charging loss: some energy turns into heat in the charger, the cable and the car’s onboard charger before it reaches the battery. On a home AC charger, expect to lose about 10 to 15%.
Units drawn from your meter for a full charge, near empty to full, assuming about 13% loss:
- 20 kWh battery: about 23 units (around ₹185 at ₹8 per unit)
- 30 kWh battery: about 34 to 35 units (around ₹280)
- 40 kWh battery: about 45 to 47 units (around ₹370)
- 50 kWh battery: about 57 to 58 units (around ₹460)
- 60 kWh battery: about 68 to 70 units (around ₹550)
- 75 kWh battery: about 85 to 87 units (around ₹690)
Your car’s battery size is on its spec sheet, usually listed as “battery capacity” in kWh. And you’ll rarely charge from empty. Topping up from 30% to 90% uses about 60% of these figures.
How to calculate EV charging units and cost yourself
You need three numbers:
- Your battery size in kWh, from the spec sheet
- How much you’re adding: for example 20% to 80% is 60% of the battery
- Your tariff in ₹ per unit, from your electricity bill
Then:
- Units needed = battery size × share you’re adding ÷ 0.87
- Cost = units needed × your tariff
Example: a 40 kWh battery charged from 20% to 80% at ₹8 per unit.
- 40 × 0.6 = 24 kWh into the battery
- 24 ÷ 0.87 = about 27.6 units from the meter
- 27.6 × ₹8 = about ₹220
The 0.87 accounts for charging losses. If your charger or app shows the units it delivered, use that number directly.
How much does it cost per km to run an electric car?
This is the number that matters for comparing with petrol. Most compact electric SUVs in Indian city driving cover roughly 6 to 7 km per unit measured at the meter, including charging losses. Bigger cars, highway speeds and heavy AC use bring that down.
- At 6 km per unit and ₹8 per unit: about ₹1.33 per km
- At 7 km per unit and ₹8 per unit: about ₹1.14 per km
Want your own number? After a few weeks of charging at home, divide the km you drove by the units your charger or app recorded. That’s your real efficiency, and it beats any brochure figure.
Is charging an EV cheaper than petrol?
For most drivers, by a wide margin. Here’s a month of driving 1,200 km:
Electric car
- 1,200 km ÷ 6 km per unit = 200 units
- 200 units × ₹8 = about ₹1,600 a month
Petrol car
- 1,200 km ÷ 15 km per litre = 80 litres
- 80 litres × ₹100 = about ₹8,000 a month
Plug in your own petrol price and mileage. The gap moves around, but at home charging rates it rarely closes.
Home vs public charging: how much does each cost?
Where you charge changes the cost more than anything else.
- Home AC charging: you pay your domestic or EV tariff. In most states that’s in the single digits per unit.
- Public AC charging: usually priced higher than home, since the operator adds a margin and GST.
- Public DC fast charging: the most expensive per unit, often ₹15 to ₹25 or more including GST, depending on the operator and location. You’re paying for speed.
DC fast chargers lose a little less energy in conversion, but the higher price per unit far outweighs that. Charge at home for daily driving and use DC fast charging on trips. Our DC fast charger guide explains when it’s w orth it.
What changes how much electricity your EV uses?
Two cars with the same battery can use very different amounts of electricity per km. The biggest factors:
- Speed: highway driving at 100 km/h uses noticeably more energy per km than city traffic
- AC use: running the AC hard in a Delhi or Chennai summer can cut your range
- Traffic: stop-and-go traffic is easier on an EV than on a petrol car, because regenerative braking recovers energy
- Load and tyres: a full car and under-inflated tyres both increase consumption
- Charging losses: older wiring or a poor charger setup can push losses above 15%
How to cut your EV charging cost
- Charge at home as much as possible. It’s the cheapest option by far.
- Ask your discom about EV tariffs or time-of-day rates. Some states offer a separate EV tariff or cheaper night rates. Our state-wise EV charging tariffs guide covers five of them.
- Use a smart charger to schedule charging. A charger with scheduling starts charging at the cheapest hour without you staying up for it.
- Check your connection. Charging on your existing domestic meter is common. Read whether a domestic meter can be used for EV charging.
- Pick the right charger size. A faster charger doesn’t use fewer units, it just delivers them faster. Our home EV charger guide explains how to choose between 3.3 kW and 7.4 kW.
Kazam’s home chargers, the Zip Pro 3.3 kW and the Zoom 7.4 kW, track every session so you can see exactly how many units your car used. For a worked example on India’s best-selling EV, see how long a Tata Nexon EV takes to charge.
