Lazy Load Savings Calculator

Summary

Estimate how many KB/MB lazy loading saves on initial page load based on your image count, size, and user scroll behavior.

How it works

1. Total payload is computed as image count multiplied by average image size.
2. Below-the-fold image count is total images times the below-fold percentage.
3. Never-loaded images equals below-fold count times the never-scroll percentage.
4. Bytes saved equals never-loaded images times average image size.
5. LCP improvement is estimated at roughly 100 ms per 100 KB saved on a 3G connection.

Use cases

• Justify adding lazy loading to a content-heavy blog or news site.
• Estimate performance gains before implementing lazy loading in a web app.
• Quickly compare lazy load impact across different page layouts.
• Support a Core Web Vitals improvement proposal with concrete numbers.

Frequently Asked Questions