Dakota Richline
“Every one of us is, in the cosmic perspective, precious. If a human disagrees with you, let him live. In a hundred billion galaxies, you will not find another.”
― Carl Sagan, Cosmos

Tesla's W·h/km is a brilliant unit

Disclosure: I’m not a huge fan of Tesla, but I give credit where credit is due.

Engineering Explained on YouTube enlightened me as to why fuel consumption is a better metric than fuel efficiency, especially for gas-powered cars. TL;DW: fuel consumption is usually more relevant, and it scales nonlinearly with fuel efficiency.

As shown by this graph of fuel efficiency (black) and fuel consumption (green), doubling the efficiency of a car DOES NOT halve the amount of gas it burns! For an electric car that’s constrained by the amount of energy it can carry, I believe that energy consumption is more important to know than efficiency. Tesla is clearly on my side; they use W·h/km while some car companies display km/kW·h, or, even worse, MPGe (miles per gallon equivalent).


Europe’s L/(100 km) is great and all, but it tickles me how elegant W·h/km is for electric cars. It directly translates the amount of consumed energy to real, skeumorphic units like watt-hours and kilometers in an easy-to-understand magnitude. Some people argue that derived units should be avoided, but I disagree. Imagine measuring your fuel/energy usage in base units that are impossible to visualize in the real world: m³/m for gas, or V·C/m for electric 😬

Measuring charging speed in km/h is also a fascinating trick! [1]

Measuring charging speed in km/h is also a fascinating trick! [1]


[1] “Tesla Model 3 Supercharging board computer in the car during the charging phase” by verchmarco is licensed with CC BY 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/2.0/

Last modified: 09/12/2021