The Truth About Google PSI: Stop Chasing 100 And Start Optimizing Smarter

Google PSI delivers a score from 0–100 based on simulated performance tests using Lighthouse. But this score often causes confusion. You might have a fast-loading Shopify site—especially for actual users—yet still see a low PSI score.

Why? Because PSI:

• Simulates load conditions, often on mobile with throttling
• Focuses on technical benchmarks, not user-perceived speed
• Can fluctuate significantly with each test
• Doesn’t always reflect real-user experience (field data)

🔄 2025 Updates to Google PSI & Lighthouse

If you’re optimizing in 2025, it’s critical to understand what’s changed:

✅ Lighthouse 12.0 (May 2024)

• First Input Delay (FID) Replaced by Interaction to Next Paint (INP)
  INP is now the Core Web Vital for responsiveness, measuring a broader range of interactions—not just the first one.
• Progressive Web App (PWA) Audits Removed
  PSI no longer reports on PWA metrics as of Lighthouse v12.
• Scoring Algorithm Adjustments
  The weight of metrics like Total Blocking Time (TBT) and Largest Contentful Paint (LCP) has increased, reflecting their growing importance in UX and SEO.

⚖️ PSI Scores vs. Real-World Performance

Let’s look at an example:

Before Optimization:

• Google PSI mobile score: 42
• Actual load time on WebPageTest: 2.3 seconds
• Shopify speed score: 52

After Optimization:

• PSI mobile score: 57
• Actual load time on WebPageTest: 1.2 seconds
• Shopify speed score: 84

Even though we nearly halved the load time, PSI barely moved.

Why? Because PSI’s lab-based scoring doesn’t capture the benefits seen by real users with fast connections and optimized caching.

🛠️ What Tools Should You Use in 2025?

Instead of chasing PSI perfection, focus on real-world performance:

• WebPageTest.org
  Get granular insights into first-byte time, fully loaded time, and content paint timings.
• Chrome User Experience Report (CrUX)
  Check how real users experience your site with real data across devices and geographies.
• Core Web Vitals Report in Search Console
  See your INP, LCP, and CLS metrics directly from Google, based on field data.
• Shopify Speed Score
  Useful for benchmarking your store’s speed relative to similar stores on Shopify.

🚫 Skip the AMP Bandwagon

Previous iterations of this post recommended AMP to boost PSI scores. But times have changed.

AMP is no longer a ranking factor in Google Search, and its usage has declined significantly. Instead of building AMP versions of your site, focus on:

• Optimizing your main site for speed and usability
• Improving Core Web Vitals across all templates
• Using modern JavaScript practices (like lazy loading and deferred scripts)

🔍 Understand Lab vs. Field Data

Lab Data = Simulated tests (like PSI and Lighthouse), useful for debugging
Field Data = Real-user metrics (like CrUX), used by Google for rankings

Relying solely on lab data gives you a partial picture. For SEO and UX improvements that actually move the needle, use a combination of both.

💡 Pro Optimization Tips for 2025

• Prioritize INP + LCP + CLS – These are the Core Web Vitals that impact your rankings.
• Eliminate unused JS and CSS – Reduces blocking time and improves INP.
• Defer non-critical scripts – Helps your site load faster visually.
• Use modern image formats (WebP/AVIF) – Smaller files = faster LCP.
• Implement lazy loading – Load only what’s needed, when it’s needed.

🧠 Final Thoughts

Google PSI is a helpful tool—but it’s not the final word on performance. If you’re serious about speed (and conversion), optimize for real people, not just synthetic scores.

Focus on what matters:

• Real load time
• Core Web Vitals
• User experience across devices

And remember: a “bad” PSI score doesn’t mean a slow site—just that you’re looking at one piece of the performance puzzle.

💬 Need Help Optimizing Your Shopify Store?

We specialize in speed optimization for Shopify stores. If you’re seeing low PSI scores but know your store is snappy, let’s talk.

👉 Contact Speed Boostr