Image savings calculator: compare bytes before and after optimization

How to use this tool

1. Measure the original and optimized file sizes for the same image and intended display use.
2. Enter both values in the selected unit, checking that you have not mixed KB and MB.
3. Add other images to calculate a combined page-level estimate.
4. Optionally enter monthly page views to estimate transfer savings under a full-download-per-view assumption.
5. Inspect the optimized images visually before treating the smaller files as suitable replacements.

The calculator does not compress images, upload files or fetch a page. It works with the numbers you enter in your browser. Compare equivalent visual content and quality requirements; a much smaller thumbnail is not necessarily an appropriate replacement for a large product photograph.

About the results

For each image, bytes saved equal the original size minus the optimized size. Percentage reduction equals that difference divided by the original size, multiplied by 100. Use a positive original size; a zero-size original does not provide a meaningful denominator for percentage reduction.

The page total combines the entered image savings. The monthly estimate multiplies that total by the page-view count you supply. These are arithmetic estimates, not observed traffic or bandwidth measurements. The interface's unit convention should be used consistently for every input.

The estimate assumes the listed images are downloaded for each counted view. Real transfer depends on browser and edge caching, responsive selection, lazy loading, repeat visits and whether a visitor reaches the relevant image. Some pages will request only a subset of the files represented in your inputs.

If the optimized file is larger, inspect the export settings and the source. A different format is not automatically smaller for every image. Keep the result as evidence rather than replacing a valid negative saving with a positive marketing claim.

Will saving half the bytes cut load time in half?

No. Resource discovery, network conditions, parallel downloads, decoding and rendering all affect timing. The largest visible image can arrive late because the browser discovers it late, even when the file is small.

Use the LCP guide to identify which stage needs work. The calculator is useful for comparing transfer changes, but it cannot predict the resulting LCP or Lighthouse score from file sizes alone.

Which image size should I compare for a responsive page?

Compare the resource selected for the same viewport and device conditions before and after the change. A page may offer several candidates through srcset, and the browser may choose different files on a high-density display.

Inspect the actual request in browser tools. The image optimization guide explains how sizes, candidate widths and the rendered slot work together. Keep separate calculations where mobile and desktop pages download materially different assets.

How should I use the monthly estimate?

Use it as a planning scenario. Record the assumed page views, the image set and whether caching or partial loading makes the full-download assumption unrealistic. Do not describe the estimate as a measured bill reduction or a guaranteed business saving.

After deployment, compare actual transfer and user-experience measurements where available. Preserve image quality, informative alternative text and stable dimensions while making the delivery more efficient.