What is LCP?
LCP, or Largest Contentful Paint, measures how long it takes for the largest visible element on a page to appear, which on a product page is normally the main product image.
Worked example, not a result
One oversized image holding up a whole page
Say a product page takes 4.8 seconds on a mobile connection before its main image appears. Investigating shows the image file is 1.4 MB, uploaded at full camera resolution and scaled down by the browser to fit a phone screen.
The fixes are unglamorous and effective. Export the image at the size it will actually be displayed. Serve a modern format. Let the browser choose an appropriately sized version for the screen. Load the main image immediately rather than deferring it, while deferring the images further down the page. Stop anything else, such as a slider script or a font, from having to finish before the image can be drawn.
Done together, that page might appear in 2.1 seconds instead. Nothing about the product, the price or the copy changed, and every visitor now sees the thing they came for in less than half the time.
The figures here are an example.
Why it matters
LCP is the number that decides whether a visitor sees a product or a blank space, and Google treats 2.5 seconds or less as good. It matters most on the first screen of a mobile product page, which is where most paid clicks and most search visits land.
That puts it at the join between the visitors lever and the conversion lever. A slow first paint means people leave before any of the persuasion on the page has a chance to work, so a store pays for traffic that never sees what it bought. Improving it lifts the value of every click already being purchased.
For a store owner the encouraging part is that this is usually one problem, not many. On most ecommerce sites the largest element is the hero product image, so getting that one file and its loading order right fixes the measurement across thousands of pages at once.
Common mistakes
- Uploading images at camera resolution. The browser downloads the whole file before scaling it, so the visitor pays for pixels they never see.
- Deferring the main product image. Lazy loading is right for images further down the page and wrong for the one that defines the first screen.
- Letting scripts and fonts block the first paint. Anything that has to finish before the image can be drawn is added directly to the measurement.
- Judging the result from a desktop test. The number that counts comes from real visits, and most of those are on phones on ordinary connections.
Related terms and answers
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