SOC explained
If you are new to electric vehicles, SOC is one of the first terms you will see in charging apps, car menus, and forum posts. SOC stands for state of charge, and it simply tells you how full the battery is, usually as a percentage. For example, 80% SOC means the battery is charged to 80% of its usable level, while 20% SOC means there is still some energy left, but not much.
That is why people often search for how many kWh are needed to charge an electric car. Battery percentage alone does not tell you the full story. To estimate charging energy, you need to know the battery size, the starting SOC, and the target SOC. Once you have those three values, you can convert percentage into kilowatt-hours and then into range and cost.
As a quick note, this article is for general planning only. Real-world charging results vary by battery chemistry, temperature, charger type, driving style, and the car’s onboard charging limits.
Battery size vs usable capacity
EV specs often list a battery size in kWh, but that number can be confusing. In many cases, the published figure is the gross or nominal battery capacity, not the amount you can actually use. The car may reserve a buffer at the top and bottom of the pack to protect battery health.
For example, a vehicle might be advertised with a 60 kWh battery, but the usable capacity could be closer to 57 kWh. That means when you calculate charging from 20% to 80%, you should usually base the math on the usable capacity, not the headline number, if you want a realistic estimate.
This matters for both range and cost. If you use the full nominal battery size in your estimate, your numbers may be slightly too optimistic. If you are planning a trip or a home charging session, a small error is fine, but a realistic estimate is better when you want to know whether you have enough energy to arrive comfortably.
SOC window to kWh formula
The simplest way to convert battery percentage into energy is to use the following formula:
kWh needed = usable battery capacity × (target SOC - starting SOC)
Make sure SOC values are written as decimals in the formula. For example, 80% becomes 0.80 and 20% becomes 0.20. If your usable battery capacity is 57 kWh and you want to charge from 20% to 80%, the calculation is:
57 × (0.80 - 0.20) = 57 × 0.60 = 34.2 kWh
So, in this case, you would need about 34.2 kWh delivered to the battery to move through that SOC window. This is the core idea behind turning electromagnetic car charging percentage into a usable planning number.
You can also estimate energy for other windows. Charging from 10% to 90% on the same 57 kWh usable battery would be:
57 × (0.90 - 0.10) = 45.6 kWh
If you only want a top-up from 50% to 70%, the result is much smaller:
57 × (0.70 - 0.50) = 11.4 kWh
That is why SOC planning is so useful. It helps you answer practical questions like: How much do I need for the next commute? How much should I add before a weekend trip? And how much will it cost at my local tariff?
Example 20–80% charge
The 20–80% charging window is popular because it balances convenience, battery care, and everyday usability. It is not a strict rule for every car or every situation, but many EV owners use it as a practical routine.
Let’s work through a realistic example. Imagine an EV with a usable battery capacity of 64 kWh. You charge from 20% SOC to 80% SOC.
- Battery window: 80% - 20% = 60%
- Energy added to the battery: 64 × 0.60 = 38.4 kWh
That means the car will gain about 38.4 kWh of stored energy. If your car uses around 16 kWh per 100 km in mixed driving, the rough range added is:
38.4 ÷ 16 × 100 = 240 km
This is only a planning estimate, not a guarantee. Highway speeds, cold weather, rain, headwinds, and cabin heating can all reduce real range. Still, it gives you a much better starting point than guessing from percentage alone.
If you are comparing routes or thinking about a longer drive, this is where an EV range calculation becomes useful. You can also pair charging estimates with a commute or trip cost tool such as commute cost calculator or a fuel comparison page like fuel cost calculator when you want to compare EV and petrol expenses.
Cost with losses
Charging does not transfer every purchased kilowatt-hour into the battery. Some energy is lost as heat, in the charger, in cables, and inside the vehicle’s charging electronics. This is why the energy shown on your electricity bill is usually higher than the energy stored in the battery.
To estimate real charging cost, divide the battery energy needed by the charging efficiency, or multiply by a loss factor. A simple planning assumption is 85% to 92% efficiency for many home and public charging situations, although the exact value depends on the setup.
Using the previous example of 38.4 kWh stored in the battery, let’s assume 90% charging efficiency:
38.4 ÷ 0.90 = 42.7 kWh from the grid
If electricity costs 70 HUF per kWh, the estimated cost is:
42.7 × 70 = 2,989 HUF
If your tariff is 95 HUF per kWh, the same session would cost:
42.7 × 95 = 4,057 HUF
This is the part many new owners miss when they ask, “mennyi kWh kell elektromos autó töltéshez?” The answer depends not only on battery size and SOC window, but also on how efficient the charging session is. Fast charging can have different losses than home AC charging, and cold batteries can temporarily increase consumption during charging.
For a more complete estimate, it helps to think in three layers:
- Battery energy needed to move from one SOC level to another
- Grid energy needed after charging losses
- Money cost based on your electricity price in HUF
If you are planning a road trip, this also helps you decide whether a short top-up is enough or whether you should charge deeper before leaving. That is especially useful for drivers comparing home charging with public charging stations.
How to estimate range from SOC
Range is always an estimate because consumption changes with speed, weather, terrain, and load. Still, you can make a useful approximation if you know your car’s average consumption. The basic method is:
Estimated range added = battery energy added ÷ consumption × 100
For example, if you add 24 kWh and your EV averages 18 kWh/100 km, the added range is about 133 km. If your consumption is 14 kWh/100 km, the same charge could add about 171 km. That difference is why EV range calculation should always be tied to your actual driving pattern.
In colder months, it is wise to leave a buffer. A trip that looks easy on paper can become tight if you drive fast on the motorway or use heating heavily. Many owners therefore charge to a comfortable margin rather than aiming for the absolute minimum.
Calculator CTA
Need a faster estimate for your own car? Use the EV charging calculator to turn SOC, battery size, and charging losses into kWh and HUF in a few seconds.
If you want, you can also compare trip costs with the commute cost calculator or check broader vehicle cost planning with other tools on the site.
Open the EV charging calculator now to see how much energy and money your next charge will need.