How to Test Your Shopify Store Speed (Tools + What Every Score Means)

Why Testing Your Shopify Store Speed Is the First Step to Fixing It

You cannot optimise what you have not measured. Before spending any time or money on speed improvements, you need a clear, accurate picture of where your Shopify store currently stands, what its specific bottlenecks are, and which pages need the most attention. The good news is that the best speed testing tools are free and require no technical knowledge to use.

The bad news is that speed testing is more nuanced than most store owners realise. A single score from a single tool on a single page does not tell you much. Meaningful speed testing requires running multiple tools, testing multiple page types, understanding what each metric means, and interpreting the results in the context of your specific store’s architecture.

This guide walks you through every tool worth using, explains what every score and metric actually measures, and tells you how to prioritise the problems you find.

Tool 1: Google PageSpeed Insights

Google PageSpeed Insights (pagespeed.web.dev) is the most important speed testing tool for Shopify stores, because it uses the same data and methodology that Google uses when evaluating your site for search ranking purposes. If you only use one tool, this is the one.

PageSpeed Insights gives you two types of data. Field data (also called Chrome User Experience Report data) reflects real user experiences on your site over the past 28 days, aggregated from Chrome users. Lab data reflects a simulated load in a controlled environment. Both are useful, but field data is what actually matters for Core Web Vitals ranking signals.

The tool scores your page from 0 to 100 in four categories: Performance, Accessibility, Best Practices, and SEO. For speed purposes, focus on Performance. The score ranges are: 0–49 (Poor, red), 50–89 (Needs Improvement, orange), 90–100 (Good, green). Aim for 90+ on both mobile and desktop.

Critically, test your mobile score as a priority. Google uses mobile-first indexing, which means your mobile performance score is the one that affects your search rankings. Many stores look fine on desktop but score 20–40 on mobile — these stores are penalised in search results whether their owners know it or not.

Understanding the Core Web Vitals Metrics

PageSpeed Insights reports on Google’s Core Web Vitals — the three metrics that directly influence your search rankings. Understanding what each one measures helps you prioritise fixes correctly.

Largest Contentful Paint (LCP) measures how long it takes for the largest visible element on the page — usually a hero image or headline — to render. LCP targets: Good is under 2.5 seconds, Needs Improvement is 2.5–4 seconds, Poor is over 4 seconds. LCP is most commonly affected by unoptimised hero images, render-blocking JavaScript, and slow server response times.

Cumulative Layout Shift (CLS) measures how much the page visually shifts as it loads — when elements jump around because images load without specified dimensions, or fonts swap and change text size. CLS targets: Good is under 0.1, Needs Improvement is 0.1–0.25, Poor is over 0.25. CLS is commonly caused by images without explicit width/height attributes, and web font loading without font-display: swap.

Interaction to Next Paint (INP) replaced First Input Delay in 2024 and measures how responsive your page is to user interactions throughout the entire page visit. INP targets: Good is under 200ms, Needs Improvement is 200–500ms, Poor is over 500ms. INP is most affected by heavy JavaScript execution that blocks the main thread.

Tool 2: GTmetrix

GTmetrix (gtmetrix.com) provides a detailed waterfall chart of every request your page makes, in the order they happen. This is invaluable for understanding the sequence of events during your page load and identifying which specific resources are causing delays.

The waterfall chart shows you each file (HTML, CSS, JavaScript, images, fonts, third-party scripts) as a horizontal bar. The length of the bar shows how long that request took. Requests in the critical path — those that block other resources from loading — are the highest-priority optimisation targets.

GTmetrix also allows you to test from different geographic locations. This is useful for global stores — a store might load quickly in North America but slowly in Europe or Asia if its assets are not being served from geographically distributed CDN nodes.

Tool 3: WebPageTest

WebPageTest (webpagetest.org) is the most technically detailed free speed testing tool available. It provides filmstrip views showing exactly how your page renders frame-by-frame, connection views showing all network activity, and advanced metrics like Time to First Byte (TTFB) and Start Render time.

TTFB — how long it takes the server to begin sending the first byte of the HTML response — is worth paying attention to for Shopify stores using server-side rendering or many Shopify scripts. A TTFB above 600ms indicates a server-side performance issue rather than a front-end asset issue, which requires a different category of fix.

Tool 4: Shopify’s Built-in Speed Score

Shopify’s admin dashboard includes a built-in Online Store Speed report, accessible via Online Store > Themes > View report. This score, provided in partnership with Google, gives you a composite performance score specific to your store along with a comparison against similar Shopify stores.

The Shopify speed score is useful as a quick benchmark, but it tests only your homepage and uses a simplified methodology compared to PageSpeed Insights. Use it for tracking overall trend direction rather than as your primary diagnostic tool.

Which Pages to Test

Most store owners test only their homepage. This is a mistake. The homepage is often the best-optimised page on a Shopify store, because it receives the most attention from developers and store owners. The pages that actually drive revenue — product pages and collection pages — are frequently much slower and receive much less attention.

Test at minimum:

• Your homepage
• Your highest-traffic collection page
• Your highest-revenue product page
• Your cart page
• Any landing page used in paid advertising campaigns

Product pages with many reviews, size guides, or app-injected widgets are often significantly slower than other pages. Running a test on your top product page frequently reveals problems that never appear on the homepage test.

How to Read the “Opportunities” Section in PageSpeed Insights

The Opportunities section in PageSpeed Insights is where the actionable information lives. Each opportunity shows a specific problem and an estimated time saving if you fix it, ranked from highest to lowest impact. Work through these top-down.

Common opportunities on Shopify stores include: Properly size images (your product images are too large), Eliminate render-blocking resources (a JavaScript or CSS file is preventing fast rendering), Reduce unused JavaScript (an app is loading code that is not used on this page), and Serve images in next-gen formats (your images are JPEG/PNG instead of WebP).

Each opportunity links to detailed documentation explaining what the problem is and how to fix it. For most Shopify store owners, fixing the top three opportunities from a product page test is enough to achieve a meaningful, measurable improvement in conversion rates.

Setting a Speed Testing Cadence

Speed testing should not be a one-time activity. Schedule a monthly speed audit as a standard part of your store management routine. Any time you install a new app, add a new section to your theme, upload a batch of new product images, or make significant changes to your store, run a speed test before and after to quantify the impact.

This discipline catches problems early — before a newly-installed app has had months to cost you conversions — and builds an institutional understanding of how different types of changes affect your store’s performance.

If the technical side of speed testing and interpretation feels overwhelming, the team at OneOnic can run a comprehensive speed audit for your store and translate the findings into a prioritised action plan. Get in touch to discuss what a performance engagement looks like for your store.