Latency numbers every frontend developer should know

Wifi latency to internet

Wifi adds minimal latency to a connection. This can increase with a weak signal or older hardware.

1-4ms

TTFB, FCP, LCP

5G high-band (millimeter wave) latency to internet

Millimeter wave is the fastest deployed mobile technology. However, it is only practical to use in dense urban areas with a line of sight to the radio tower.

1-5ms

TTFB, FCP, LCP

User-space budget per frame for 60 frames per second

On a 60fps device, a frame is painted every 16ms. However, the device needs some time for the actual processing of the frame. The time here is the time available for your code to compute what should be painted.

5-10ms

Smooth framerate

5G mid-band latency to internet

This is the regular 5G latency. Experience may vary in case of bad signal or an overloaded tower.

10-30ms

TTFB, FCP, LCP

Round trip latency to a service or database in same cloud region

This is the latency to a different service that is deployed close to you without going to the internet.

10ms

TTFB, FCP, LCP

LTE latency to internet

Typical latency for LTE, aka 4G cellular networks.

15-50ms

TTFB, FCP, LCP

Frame-duration at 60 frames per second

60 frames per second is the most popular frame rate for display devices. However, some newer devices support higher frame rates like 90 or 120 fps.

16ms

Smooth frame rate

Round trip latency to other city on the same continent

This is the latency you can expect if you deploy to a region on the same continent as your user. It's calculated for a distance of 5000 kilometers, so the actual latency may be slightly higher or lower.

33ms

TTFB, FCP, LCP

Shortest duration of time perceived by humans as time having passed

When responding to user input, staying below this duration means that your user will perceive the response as instant. Citation

40-80ms

INP

Time to parse 1MB of CSS

Parsing CSS is part of the work the browser has to perform to render a web page.

100ms

FCP, LCP

Time to parse 1MB of HTML

Parsing HTML is part of the work the browser has to perform to render a web page. While it is often negligible for shorter web pages, it can become a major factor for very long articles.

120ms

FCP, LCP

3G latency to internet

3G is the slowest cellular standard in common use today.

150ms

TTFB, FCP, LCP

Round trip latency to other side of earth with a high quality network (cold potato routing)

This is the worst-case latency you should see if you deploy a service to a single region.

150ms

TTFB, FCP, LCP

Time to parse 1MB of JS

Parsing JavaScript can have a major impact on page load time as it often grows more quickly than CSS and JS. Code-splitting is the primary technique to minimize JS size.

150ms

FCP, LCP, INP

Duration of time perceived by humans as sluggish

When reacting to user input, a response slower than this value will be perceived as having to wait. 200ms is also the threshold for "Needs improvement" in INP.

200ms

INP

Round trip latency to other side of earth without leased fiber (hot potato routing)

When users directly connect to a faraway server or when using a low-cost CDN, then latencies for users may double from passing bytes through the cheapest path possible.

300ms

TTFB, FCP, LCP