Skip to content
UX Atlas
UI foundationEstablished researchIntermediate

Performance as User Experience

Speed is a usability property, and the metrics that matter are the ones measured on real devices.

Definition

Performance determines whether an interface feels responsive. Core Web Vitals measure three aspects of that experience: loading, interactivity and visual stability, as experienced by real users rather than in a lab.

Established research. Originates in published research and has been replicated. The effect is real. Its size in your product still needs measuring.

On this page
  1. Definition
  2. Core Web Vitals thresholds
  3. Design decisions that dominate these numbers
  4. Sources
  5. Continue from here

Core Web Vitals thresholds

Measured at the 75th percentile of real user experiences.

MetricMeasuresGood
LCP, Largest Contentful PaintWhen the main content appearsUnder 2.5 seconds
INP, Interaction to Next PaintResponsiveness to input across the visitUnder 200 milliseconds
CLS, Cumulative Layout ShiftUnexpected movement of contentUnder 0.1

Design decisions that dominate these numbers

  • Hero image size and loading strategy, which usually determines LCP.
  • Web font loading, which delays text rendering and can shift layout.
  • Reserved space for images, ads and embeds, which is the main lever on CLS.
  • Amount of client-side JavaScript, which drives INP.
  • Third-party scripts, which are frequently the largest single cost and the least examined.

Sources

Where a source establishes something narrower than the popular reading of it, the note says so.

Continue from here

Each link says what the connection is, so you can tell a principle from an alternative from a thing people mix this up with.

Applied through

Where this shows up as a concrete interface decision.

Principles behind this

The reasoning this solution is an application of.

Often used with

These usually appear in the same screen or the same decision.

Check your work

Review passes that test whether this was done properly.

Short definition

The one-paragraph version, for when that is all you need.

Related concept

Connected closely enough to change how you apply this.