Every EV range calculation comes down to one idea: you have a certain amount of usable energy on board, and the car spends it at a certain rate. Divide — or multiply — the two and you have your range. Here’s how to do it properly, including the adjustments that make the estimate match reality.
The basic EV range formula
Start with the energy you plan to use:
- Usable energy (kWh) = battery capacity × SOC window ÷ 100
- Range = usable energy × distance per kWh
A worked example: a 77 kWh battery driven from 80% down to 10% gives a 70% window, which is about 54 kWh of usable energy. At a real-world average of 6 km/kWh (3.7 mi/kWh), that’s roughly323 km of driving. If your efficiency figure is a consumption like 16 kWh/100km instead, divide: 54 kWh ÷ 16 kWh/100km × 100 = 337 km.
The EV range calculator does both forms automatically — enter your efficiency in any unit and it converts for you.
Step 1: Know your usable battery capacity
Manufacturers quote gross capacity, but most cars hold back a buffer of a few percent to protect the pack. If you know your car’s usable figure, use it; otherwise the advertised capacity gets you within a few percent, which is fine for trip planning. You can also measure effective capacity over time by tracking how many kWh a known SOC window covers.
Step 2: Use your own efficiency, not the brochure’s
The official WLTP or EPA efficiency comes from a lab cycle. Your number comes from your roads. Measure it once from a real trip — the efficiency calculator works it out from battery capacity, SOC change and distance — and re-measure when the seasons change. If you’re unsure what the units mean, our explainer on EV efficiency units covers kWh/100km, Wh/km and mi/kWh in plain English.
Step 3: Plan a sensible SOC window
Few drivers actually run 100% to 0%. DC fast charging slows dramatically above 80%, and nobody enjoys arriving on 1%. Planning between80% and 10% is a realistic default for road trips, while daily driving between 20% and 80% keeps the battery happiest. Shrink the window in winter or on unfamiliar routes to buy yourself margin.
Adjusting for weather and speed
Two factors move the result more than everything else combined:
- Temperature. Expect 10–30% more consumption in freezing weather. Preconditioning while plugged in and using heated seats over the cabin heater claw much of it back.
- Speed. Aerodynamic drag rises with the square of speed, so consumption climbs steeply past 110 km/h. Dropping from 130 to 110 km/h can add 15% more range.
The practical approach: keep two efficiency figures — a summer and a winter one — and run the calculation with the season’s number before any long drive.
Putting it together
Capacity, efficiency and a sensible SOC window: that’s the whole method. Run it before a trip and you’ll know whether to charge to 90% tonight or stop once for ten minutes tomorrow. And if the estimate is tighter than you’d like, our guide to improving EV efficiency shows which habits unlock the most extra kilometres.