Core Web Vitals Assessment Calculator
Rate LCP, INP and CLS (plus FCP and TTFB) against Google's thresholds, working out the 75th percentile from raw field measurements if you paste them.
For each metric, enter its 75th-percentile value, or paste raw measurements (separated by commas, spaces or new lines) and the 75th percentile is worked out for you. Leave a metric empty to skip it.
Calculated entirely in your browser — nothing you enter here is sent to a server.
How the assessment works
Core Web Vitals are three field metrics Google uses to describe loading, responsiveness and visual stability. Each is judged at the 75th percentile of page loads, so at least three in four visits must meet the target. A page passes the Core Web Vitals assessment only when LCP, INP and CLS are all good at that percentile. The thresholds below are the ones Google publishes on web.dev.
| Metric | Good | Needs improvement | Poor |
|---|---|---|---|
| Largest Contentful Paint (LCP) | ≤ 2.5 s | 2.5–4.0 s | > 4.0 s |
| Interaction to Next Paint (INP) | ≤ 200 ms | 200–500 ms | > 500 ms |
| Cumulative Layout Shift (CLS) | ≤ 0.1 | 0.1–0.25 | > 0.25 |
| First Contentful Paint (FCP), diagnostic | ≤ 1.8 s | 1.8–3.0 s | > 3.0 s |
| Time to First Byte (TTFB), diagnostic | ≤ 0.8 s | 0.8–1.8 s | > 1.8 s |
When you paste raw measurements, the 75th percentile is calculated with linear interpolation between the closest ranks (the definition Excel's PERCENTILE.INC and NumPy use by default).
Worked example
Thirteen LCP measurements exported from a real-user monitoring tool, in milliseconds: 1820, 2410, 1990, 3120, 2650, 2200, 1750, 4890, 2310, 2050, 2780, 1900, 2600. Their 75th percentile is 2,650 ms, so LCP needs improvement even though most individual loads were under 2.5 s. With INP at 210 ms and CLS at 0.12 at the 75th percentile, the page fails the assessment: all three are just over their good thresholds.
Reading the result
- Use field data from real visitors (for example from the Chrome UX Report, Search Console, or your own monitoring). A single lab test from your own device is not a 75th percentile.
- Assess mobile and desktop separately; Google reports them separately.
- FCP and TTFB are diagnostic: they help explain a slow LCP but don't decide the assessment.
Limitations
- The calculator rates the numbers you give it; it doesn't measure a website.
- Google's own reports group measurements into histograms, so their 75th percentile can differ slightly from one computed from individual samples.
- A good assessment says nothing about content quality or relevance, and passing it doesn't guarantee rankings.
Large images are a common cause of slow LCP: shrink them with the image compressor, resize them with the image resizer, or convert them to WebP with the image format converter.
How to use the Core Web Vitals Assessment Calculator
- Choose whether your LCP, FCP and TTFB figures are in seconds or milliseconds. INP is always in milliseconds and CLS has no unit.
- For each metric, type its 75th-percentile value, or paste raw field measurements and the tool works out the 75th percentile.
- Read each metric's rating against Google's thresholds and the overall Core Web Vitals verdict.
- Copy the summary to share it.
Example: Raw LCP measurements
Thirteen LCP samples in milliseconds — 1820, 2410, 1990, 3120, 2650, 2200, 1750, 4890, 2310, 2050, 2780, 1900, 2600 — have a 75th percentile of 2,650 ms, which needs improvement. With INP at 210 ms and CLS at 0.12, the page fails the assessment.
Questions about the Core Web Vitals Assessment Calculator
- Why the 75th percentile?
- Google judges each metric at the 75th percentile of page loads, so a page is good only if at least three in four visits meet the target. A single fast load from your own device doesn't show that.
- When does a page pass the Core Web Vitals assessment?
- When LCP, INP and CLS are all good at the 75th percentile. If you leave one out, the result is marked incomplete rather than passed.
- Are FCP and TTFB part of Core Web Vitals?
- No. They are diagnostic metrics that help explain a slow LCP. They are rated here for convenience but don't affect the verdict.
- Where do I get field data?
- From real-user measurements: the Chrome UX Report, Search Console's Core Web Vitals report, PageSpeed Insights' field data section, or your own monitoring.
- Why might my number differ from Google's report?
- Google computes percentiles from grouped histogram data, and reports mobile and desktop separately. A percentile from your own samples can differ slightly.
- Does passing improve rankings?
- Google says page experience is one of many signals, and relevant content matters more. Passing describes the user experience; it doesn't guarantee a ranking change.