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Image planning & checks

Compression Percentage Calculator

Compare the file you started with and the file you finished with. See the percentage saved, the compression ratio and the byte difference—even when the output became larger.

Calculate on your device

KB and MB use 1,000 bytes per KB. KiB and MiB use 1,024 bytes per KiB. Match the units shown by your device.

Enter valid values to see the calculation. Results update as you type.

Calculations and image inspection run in this browser. Continuing to another tool saves a temporary local copy. No account is needed.

How to use this calculator

  1. Enter the original file size and select its unit.
  2. Enter the downloaded output size with its own unit. Match decimal KB/MB or binary KiB/MiB to your file manager.
  3. Read the percentage and bytes saved, then inspect the output to decide whether the reduction was worth the quality trade-off.

A ratio and a percentage describe the same change differently

The compression ratio is original bytes divided by output bytes. Percentage saved is (1 − output bytes ÷ original bytes) × 100. A 4:1 ratio means the output is one-quarter of the original, so the saving is 75%.

An output can be larger after re-encoding. That is a size increase, not a successful zero-percent reduction. This calculator shows growth explicitly so you can keep the smaller original or try different settings.

This is a comparison tool, not a compressor. It cannot predict whether a target is achievable or assess readability. Compare files that contain the same intended content, and retain the original before attempting stronger compression.

Common questions

Why are KB and KiB different?

One KB is 1,000 bytes; one KiB is 1,024 bytes. One MB is 1,000,000 bytes and one MiB is 1,048,576 bytes. Mixing them changes the calculated saving.

What if my output is larger than the original?

The result shows a percentage increase and the extra bytes. Already compressed data, format changes and added metadata can produce larger output.

Does a 90% saving mean good quality?

No. A percentage describes bytes only. Check readable text, image details, page count or playback before using the smaller copy.

Put the result to work

Compress an image →

Create a smaller image to compare.

Compress a PDF →

Reduce a document and verify its readability.

Compress a video →

Adjust video encoding and check the result.