Page Speed Score Calculator
Estimates a composite page speed score from Core Web Vitals — LCP, FID, and CLS — weighted by their SEO impact. Use it to diagnose performance gaps before auditing your site or comparing mobile vs. desktop results.
About this calculator
Google's Core Web Vitals define three measurable aspects of user experience: Largest Contentful Paint (LCP) measures loading speed, First Input Delay (FID) measures interactivity, and Cumulative Layout Shift (CLS) measures visual stability. This calculator combines them into a single 0–100 score using weighted penalties: Score = max(0, min(100, (100 − (LCP / 100 × 40) − (FID / 100 × 20) − (CLS × 25)) × deviceMultiplier)), where the device multiplier is 0.95 for mobile and 1.0 for desktop. LCP carries the heaviest weight (40 points) because loading speed is the most user-visible metric. CLS contributes 25 points and FID 20 points. A mobile penalty of 5% reflects the real-world performance gap on slower devices and networks. Scores above 90 are considered good; 50–89 needs improvement; below 50 is poor.
How to use
Imagine your desktop site has LCP = 2.5 s, FID = 80 ms, and CLS = 0.08. Plug these into the formula: 100 − (2.5 / 100 × 40) − (80 / 100 × 20) − (0.08 × 25) = 100 − 1.0 − 16.0 − 2.0 = 81.0. Because you selected Desktop, the multiplier is 1.0, giving a final score of 81. If you switch to Mobile, multiply by 0.95: 81 × 0.95 = 76.95 ≈ 77. This tells you your desktop experience is acceptable but your mobile experience needs improvement, so reducing FID should be your priority.
Frequently asked questions
What are Core Web Vitals and why do they matter for SEO?
Core Web Vitals are a set of real-world performance metrics defined by Google to quantify user experience: LCP (loading), FID (interactivity), and CLS (visual stability). Google officially incorporated Core Web Vitals into its ranking algorithm in 2021 as part of the Page Experience update. Pages that pass the 'Good' thresholds — LCP under 2.5 s, FID under 100 ms, CLS under 0.1 — are eligible for a ranking boost over otherwise equivalent pages. Improving these metrics also directly reduces bounce rates and increases conversions.
What is a good page speed score for ranking on Google?
A score of 90 or above is generally considered 'Good' and aligns with passing all three Core Web Vitals thresholds. Scores between 50 and 89 signal that at least one metric needs attention and may be costing you ranking positions in competitive niches. Below 50 is classified as 'Poor' and is likely hurting both rankings and user retention. Google's own PageSpeed Insights tool uses a similar 0–100 scale and is the authoritative source for your actual score.
Why is the mobile page speed score lower than desktop for the same metrics?
Mobile devices typically have slower CPUs, less RAM, and rely on cellular connections that introduce higher latency than broadband. This calculator applies a 5% mobile penalty to reflect that identical raw metrics translate to a noticeably worse perceived experience on a phone than on a desktop. Google also uses mobile-first indexing, meaning it primarily evaluates the mobile version of your page for ranking purposes. Optimizing specifically for mobile — through responsive images, reduced JavaScript, and server-side rendering — is therefore more impactful for SEO than desktop optimization alone.