Largest Contentful Paint (LCP)
Largest Contentful Paint (LCP) reports the render time of the largest image or text block visible in the viewport, measured from when the page starts loading. It is one of Google's Core Web Vitals, exposed through the Largest Contentful Paint API, and the candidate element can change as larger content paints — the final value is taken at the last candidate before user interaction. web.dev breaks LCP into TTFB, resource load delay, load duration, and render delay to localise the bottleneck.
What this means
LCP measures when the largest contentful element in the viewport — typically a hero image, a video poster, or a large text block — finishes rendering, timed from navigation start. The browser reports a sequence of candidates and the largest one painted before the first user interaction becomes the metric.
Its four sub-parts
web.dev decomposes LCP into time to first byte, resource load delay, resource load duration, and element render delay. That breakdown shows whether the problem is the server, the time before the resource starts downloading, the download itself, or the rendering after it arrives — each has different fixes.
- Core Web Vital: render time of the largest viewport element
- Candidate can change as larger content paints in
- Sub-parts: TTFB, load delay, load duration, render delay
Why it misleads
LCP tracks one element, so a layout where the largest block is not the most important content can mislead. Lazy-loaded or late-discovered hero images inflate it, and the value reflects the visitor's network and device — read field LCP as a distribution, not a single lab pass.
How it appears in analytics and logs
A slow LCP means the principal content took a long time to appear — caused by slow TTFB, late-discovered hero images, render-blocking resources, or client-side rendering that delays the main element.
Diagnostic use case
Use LCP to judge when the main content becomes visible, and decompose it into its four sub-parts to find whether the server, resource loading, or rendering is the limiting phase.
What WebmasterID can help detect
WebmasterID can record LCP as a first-party timing event so the Core Web Vital is read against human-classified sessions rather than bot or prerender traffic.
Common mistakes
- Lazy-loading the LCP element and delaying its discovery.
- Reading one lab LCP instead of the field distribution.
- Forgetting LCP includes the TTFB it is built on top of.
Privacy and accuracy notes
LCP is a per-page render timing from the browser, not personal data. Discussion here is educational, not legal advice.
Related pages
- First Contentful Paint (FCP)
First Contentful Paint (FCP) measures the time from navigation start to when the browser first renders any DOM content — text, an image, a non-white canvas, or SVG. The Paint Timing API exposes it as the first-contentful-paint entry, and web.dev treats it as the moment a visitor first sees that something is happening. It precedes Largest Contentful Paint, which marks the largest element, so the two answer different questions about perceived load.
- Cumulative Layout Shift (CLS)
Cumulative Layout Shift (CLS) measures the largest burst of unexpected layout shifts during a page's lifetime. Each shift contributes a layout-shift score equal to the impact fraction times the distance fraction, and the Layout Instability API reports those entries. To avoid penalising long-lived pages, CLS is the maximum sum within a session window of shifts rather than a running total, which is why a stable page that occasionally moves can still score low.
- Interaction to Next Paint (INP)
Interaction to Next Paint (INP) measures a page's responsiveness by observing the latency of every click, tap, and key press during a visit and reporting a representative high value — close to the worst. Latency spans from the input to the next frame the browser paints. INP became a Core Web Vital in March 2024, replacing First Input Delay, because it captures the full processing-plus-render cost across all interactions, not just the delay of the first one.
- Website observability
Core Web Vitals beside human traffic.
Sources and verification notes
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.