Work out core web vitals estimate instantly with clear inputs, formula shown and shareable results.
Largest contentful paint is modelled as time to first byte plus the transfer time for above-the-fold assets plus client render time, with Google's thresholds at 2.5 and 4.0 seconds. Transfer time dominates on slow connections, which is why cutting above-the-fold weight moves LCP more than any amount of server tuning.
Transfer time
ms = above-the-fold KB x 8 / Mbps
LCP estimate
LCP = TTFB + transfer time + render time
ms = above-the-fold KB x 8 / Mbps. Largest contentful paint is modelled as time to first byte plus the transfer time for above-the-fold assets plus client render time, with Google's thresholds at 2.5 and 4.0 seconds.
Transfer time dominates on slow connections, which is why cutting above-the-fold weight moves LCP more than any amount of server tuning.
Enter page weight above the fold, connection speed, time to first byte, client render time. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.