📘 Field descriptions for Core Web Vitals field data from the Chrome User Experience Report (CrUX) — LCP, FCP, CLS, and FID, including p75 values, density distributions, and score thresholds.

Overview

Web Vitals Field Data comes from the Chrome User Experience Report (CrUX), a real-user measurement dataset collected by Google. These fields reflect how actual visitors experience your pages, not lab simulations. Each vital has a p75 value (the 75th percentile of user experiences) and a density breakdown across Google's three performance tiers: Good, Needs Improvement, and Poor.

Field data is only available for URLs with enough traffic to be included in CrUX. Pages below the traffic threshold will show no data for these fields.

Dataset and API collection

Available in: SiteCrawler・RealKeywords
For API users: These fields are available in the core_web_vitals BQL collection.

Largest Contentful Paint (LCP)

Measures how long it takes the page to render its largest visible element. Good: under 2,500ms · Poor: over 4,000ms

Field name	API identifier	Kind	Type	Description
LCP: Value Also shown as: LCP: Avg	`web_vitals.field_data.lcp_p75`	metric	float	The 75th percentile LCP value in milliseconds — the LCP experience at or better than 75% of page loads.
LCP: Good Density	`web_vitals.field_data.lcp_good_density`	metric	float	The proportion of user experiences with a Good LCP score (under 2,500ms), expressed as a ratio between 0 and 1.
LCP: Needs Improvement Density	`web_vitals.field_data.lcp_ni_density`	metric	float	The proportion of user experiences with a Needs Improvement LCP score (2,500–4,000ms), expressed as a ratio between 0 and 1.
LCP: Poor Density	`web_vitals.field_data.lcp_poor_density`	metric	float	The proportion of user experiences with a Poor LCP score (over 4,000ms), expressed as a ratio between 0 and 1.

First Contentful Paint (FCP)

Measures how long it takes the page to render any part of its content. Good: under 1,000ms · Poor: over 3,000ms

Field name	API identifier	Kind	Type	Description
FCP: Value Also shown as: FCP: Avg	`web_vitals.field_data.fcp_p75`	metric	float	The 75th percentile FCP value in milliseconds.
FCP: Good Density	`web_vitals.field_data.fcp_good_density`	metric	float	The proportion of user experiences with a Good FCP score (under 1,000ms).
FCP: Needs Improvement Density	`web_vitals.field_data.fcp_ni_density`	metric	float	The proportion of user experiences with a Needs Improvement FCP score (1,000–3,000ms).
FCP: Poor Density	`web_vitals.field_data.fcp_poor_density`	metric	float	The proportion of user experiences with a Poor FCP score (over 3,000ms).

Cumulative Layout Shift (CLS)

Measures visual stability — how much the page layout shifts during loading. Good: under 0.1 · Poor: over 0.25

Field name	API identifier	Kind	Type	Description
CLS: Value Also shown as: CLS: Avg	`web_vitals.field_data.cls_p75`	metric	float	The 75th percentile CLS score. A score of 0 means no layout shift; higher values indicate more instability.
CLS: Good Density	`web_vitals.field_data.cls_good_density`	metric	float	The proportion of user experiences with a Good CLS score (under 0.1).
CLS: Needs Improvement Density	`web_vitals.field_data.cls_ni_density`	metric	float	The proportion of user experiences with a Needs Improvement CLS score (0.1–0.25).
CLS: Poor Density	`web_vitals.field_data.cls_poor_density`	metric	float	The proportion of user experiences with a Poor CLS score (over 0.25).

First Input Delay (FID)

Measures the time from when a user first interacts with the page to when the browser responds. Good: under 100ms · Poor: over 300ms

Field name	API identifier	Kind	Type	Description
FID: Value Also shown as: FID: Avg	`web_vitals.field_data.fid_p75`	metric	float	The 75th percentile FID value in milliseconds.
FID: Good Density	`web_vitals.field_data.fid_good_density`	metric	float	The proportion of user experiences with a Good FID score (under 100ms).
FID: Needs Improvement Density	`web_vitals.field_data.fid_ni_density`	metric	float	The proportion of user experiences with a Needs Improvement FID score (100–300ms).
FID: Poor Density	`web_vitals.field_data.fid_poor_density`	metric	float	The proportion of user experiences with a Poor FID score (over 300ms).

Data Availability

Field name	API identifier	Kind	Type	Description
Report Available	`web_vitals.field_data.is_available`	dimension	boolean	Whether CrUX field data is available for this URL. Filter on this field to limit analysis to URLs with sufficient real-user data.
Normalized URL	`web_vitals.field_data.normalized_url`	dimension	string	The base URL under which CrUX aggregates user experiences. URLs that differ only by query parameters are treated as a single page and their data is combined here.

See also:

Web Vitals - Field Data Fields