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 does not have an inverse relationship like fuel efficiency.

As shown by this graph of fuel efficiency (green) and fuel consumption (black), increasing efficiency by a certain amount does not always change fuel consumption by the same amount! 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: 10/06/2021