Compare image format savings and their effect on page load.
Format conversion and correct sizing multiply rather than add, so combining them typically removes two thirds of image weight. Because images are usually the largest contentful element, the saving translates almost directly into LCP. Correct sizing usually saves more than format conversion, and it is often overlooked because the oversized image still looks correct on screen.
Image Optimization
Optimised weight = original × (1 − format saving) × (1 − sizing saving)
Optimised weight = original × (1 − format saving) × (1 − sizing saving) Format conversion and correct sizing multiply rather than add, so combining them typically removes two thirds of image weight. Because images are usually the largest contentful element, the saving translates almost directly into LCP.
Correct sizing usually saves more than format conversion, and it is often overlooked because the oversized image still looks correct on screen.
This calculator takes 5 inputs: Original image weight, Target format, Additional saving from correct sizing, Connection speed, Monthly pageviews. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.