ARTICLE
How to Read a Page Speed Score (Without Being a Developer)
What every field in a Page Speed Grader report actually means, where the thresholds come from, and which numbers to fix first when you can only fix one.
Apr 27, 20267 min readTOOLS & AUDITS
A page speed score is four numbers, not one
Most page speed reports show a single 0–100 score and call it a day. That score is a weighted average of four underlying metrics, and the weights matter. A site with a 65 might be one CSS change away from 90, or it might need a full rebuild — the overall score doesn't tell you which.
The Page Speed Grader returns the underlying metrics directly. This post walks through each one: what it measures, what the thresholds are, and what to do when your site fails it.
The four metrics that matter
Google's Core Web Vitals framework defines three metrics with explicit thresholds. The Page Speed Grader reports these plus one additional that's diagnostic-only:
| Metric | What it measures | Pass | Needs improvement | Fail |
|---|---|---|---|---|
| LCP (Largest Contentful Paint) | Time until the biggest visible element finishes rendering | ≤ 2.5s | 2.5–4.0s | > 4.0s |
| CLS (Cumulative Layout Shift) | How much the layout jumps around during load | ≤ 0.1 | 0.1–0.25 | > 0.25 |
| INP (Interaction to Next Paint) | Time between a click/tap and the visual response | ≤ 200ms | 200–500ms | > 500ms |
| TBT (Total Blocking Time) | Diagnostic proxy for INP in lab conditions | ≤ 200ms | 200–600ms | > 600ms |
The first three are field metrics — they come from real users. TBT is a lab metric — measured in a controlled test environment. They tell you different things and you need both.
LCP: which thing took the longest to draw
LCP is the time it took for the largest visible element above the fold to render. That element is almost always one of three things:
- The hero image
- A large block of text in the H1 area
- A background image set in CSS
The grader reports the actual element it identified as the LCP candidate. If your LCP is 4.2s and the candidate is <img src="/hero.jpg">, you have one problem. If the candidate is <h1> and your H1 is plain text, you have a different problem (probably a render-blocking font or slow server response).
Fixes for slow LCP:
- Hero image too large. Convert to WebP, resize to display dimensions, add to the tag.
Keep reading
How to Read the Meta Tag Analyzer Output
What every field in a Meta Tag Analyzer report means, what the thresholds are, and how to act on each finding without guessing.
How to Fix Slow Largest Contentful Paint (LCP)
Where slow LCP comes from, how to identify the offending element, and the five fixes that resolve LCP problems on real sites — in priority order.
How to Fix Cumulative Layout Shift (CLS > 0.1)
What causes CLS, how to find the offending element, and the four fixes that resolve 95% of layout-shift problems on real sites.