Network latency dominates the modern web experience
Page load times and responsiveness to user actions are primary drivers of user satisfaction on the web—and both are commonly dominated by network latency. Latency is a function of the user's connection type (WiFi, LTE, 5G), the distance to the server, and the quality of the network in between.
Individual latency numbers may seem low in isolation, but they compound quickly. For instance, a network waterfall of depth 3 on a 300ms link yields a total latency of 900ms. Technologies such as React Server Components can move these waterfalls to the server, where the same request pattern might be 100 times faster.
Measurement notes
Device-dependent figures were measured on a 2023 high-end Android phone. Most laptops will be faster, iPhones will also be faster, while many other devices will be slower.
Source and further reading
This is a frontend take on Jeff Dean's "Latency Numbers Every Programmer Should Know." For many more numbers in a similar vein, see Napkin Math.
