The size read-only property of the LargestContentfulPaint interface returns the intrinsic size of the element that is the largest contentful paint.

The size of the element is the width times height of the rectangle that this element creates on the screen.

An integer representing the width times height of the element.

This example uses a PerformanceObserver notifying of new largest-contentful-paint performance entries as they are recorded in the browser's performance timeline. The buffered option is used to access entries from before the observer creation.

const observer = new PerformanceObserver((list) => {
  const entries = list.getEntries();
  const lastEntry = entries[entries.length - 1]; // Use the latest LCP candidate
  console.log(lastEntry.size);
});
observer.observe({ type: "largest-contentful-paint", buffered: true });