# kWh/100mi vs miles/kWh vs MPGe: How to Read EV Efficiency By Gregory Wilson · Excerpt from Chapter 4 of *EV Curious?* With gas cars, we mostly understood miles per gallon. EVs throw three different efficiency units at you, and different cars display them differently. Here's how they actually relate. ## The three units, untangled The most useful unit for an EV is **miles per kWh (mi/kWh)**. It's the direct equivalent of MPG. A really efficient EV might get 4+ miles per kWh; a less efficient one might only manage 2.5. **Kilowatt-hours per 100 miles (kWh/100mi)** is the same number expressed differently. Many EVs default to this display because it scales nicely (smaller numbers = better) and matches how energy companies bill you. If your car gets 4 miles per kWh, that's 25 kWh/100mi. If it gets 2.5 mi/kWh, that's 40 kWh/100mi. **MPGe (Miles Per Gallon Equivalent)** is the EPA's attempt to let you compare EVs to gas cars in familiar terms. It converts the energy in one kWh to the equivalent energy in a gallon of gasoline. Most modern EVs land at 100–130 MPGe versus a gas car's 25–35 MPG. But MPGe is just a unit conversion — miles per kWh is more useful for understanding actual energy use and charging costs. ## The basic range math Range is just multiplication: get 3 miles per kWh and have a 75 kWh battery? Expect roughly 225 miles under normal conditions. ## Cold weather: the range killer In freezing weather, your range can drop 20–40%. The battery becomes less efficient at low temperatures and the cabin heating system draws significant power (gas cars get "free" heat from waste engine heat). Pre-conditioning the battery and cabin while still plugged in uses grid power instead of battery power. ## Speed and aerodynamics: the math gets brutal Aerodynamic drag scales with the square of speed, and the power needed to push through it scales with the cube. Doubling speed from 40 to 80 mph creates four times the drag and requires eight times the power. So going from 70 mph to 75 mph isn't a small change — it can increase energy use by around 15%. Headwinds matter for the same reason. Towing is brutal — a trailer can cut your range by 50% or more, depending on its size and shape. ## EPA range vs WLTP vs the real world The EPA test is done in lab conditions that don't quite reflect real-world driving. Europe's WLTP cycle typically produces higher range numbers; in my experience, EPA is much closer to what I actually see, while WLTP overstates real-world range by 15–25% in most cases. Publications like Edmunds, Out of Spec Reviews, Car and Driver, and MotorTrend now publish a standardized 70 mph highway range test alongside the EPA number. The methodology is simple: charge to 100%, run at a steady 70 mph in mild weather until empty, measure how far it went. If you're comparing two cars for road-trip duty, the 70 mph number is usually a lot closer to what you'll experience. ## Why your range estimate doesn't match the math If your EV has a 300-mile EPA range and you're sitting at 50% battery, you might see 118 miles instead of 150. Your battery isn't broken — your car is being smart. The range estimator constantly recalculates based on your recent driving. If you've been driving aggressively or tackling hilly terrain, the car learns and adjusts. The estimate will also change based on your planned route if you've entered a destination — about to climb a mountain, the estimate drops; heading downhill, it rises. --- This is an excerpt from Chapter 4 of *EV Curious? — What I Learned from Seven EVs* by Gregory Wilson. - [Kindle — $9.99](https://a.co/d/gxrEPR0) - [Paperback — $18.99](https://a.co/d/051xLUs) ## Related chapters - [What driving an EV actually feels like](https://evcurious.blog/driving-an-ev/) - [How regenerative braking works in an EV](https://evcurious.blog/regenerative-braking/) - [EV plugs and adapters: NACS, J1772, CCS explained](https://evcurious.blog/ev-charging-adapters/) - [Busting the top 10 EV myths](https://evcurious.blog/ev-myths/) - [How to plan your first EV road trip](https://evcurious.blog/ev-road-trip-planning/)