Three metrics, and they are not equally important commercially.
LCP — the one that matters
Largest Contentful Paint: how long before the main content appears. On a product page that is usually the hero image.
This is the metric that correlates with revenue, because it is the closest proxy for "how long until this page looks usable". Target under 2.5 seconds on a mid-range phone over mobile data, not on your laptop.
CLS — the one that causes mis-taps
Cumulative Layout Shift: how much the page jumps while loading. On a store the practical damage is someone reaching for a variant swatch and hitting the wrong one because a banner loaded above it.
Usually caused by images without dimensions, late-loading banners and fonts swapping. All fixable and none expensive.
INP — the one people ignore
Interaction to Next Paint replaced First Input Delay. It measures how quickly the page responds when someone taps. On a store laden with third-party scripts this is frequently the failing metric, and it is the one app bloat hits hardest.
Measure it properly
Field data over lab data. Shopify's own Web Performance dashboard reports from real visitors. PageSpeed Insights gives you a lab score from a simulated device, which is useful for diagnosis and not for judging whether you have a problem.
Be wary of optimising for the PageSpeed score rather than the experience. Several apps improve the number by deferring work until after the test stops measuring, which changes the score and not the page.
What usually fixes it on Shopify
Delete apps you do not use. Size images to what they display at. Remove duplicate tracking. Defer third-party scripts so they do not block rendering. Set explicit dimensions on everything.
That list is in order and the first four are free.
Talk it through
Send us your Web Vitals report.
We will tell you which metric is actually failing, what is causing it, and how much is free to fix before anything paid.
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About the author
Manpreet Singh
Founder of Proscube. Leads the studio's Shopify, headless and CRO engineering, and works directly with founders rather than through account managers.
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