Image Compression Guide

Learn how image dimensions, file format and quality affect file size and visual quality when preparing images for the web or email.

Image compression reduces the amount of data required to store or transmit a picture. There are two main levers: pixel dimensions and encoding quality. Reducing either can make an image smaller, but each can also affect visual quality.

Resize before compressing when appropriate

If a photograph is thousands of pixels wide but will only be displayed in a small space, reducing its dimensions can save more space than quality reduction alone. Keep the original image so you can create a different output later.

Choose a suitable format

Photographs often compress efficiently as JPEG or WebP. Graphics that need transparency or very sharp edges can be better suited to PNG. The best choice depends on the image and where it will be used.

Inspect the final file

Compare text, edges, faces and fine details after compression. A smaller file is not automatically better if the output becomes difficult to read or visibly degraded.

Check the result before using it

A calculator is most useful when the inputs match the question you are trying to answer. Check units, dates, rates, periods and rounding before copying a result into a document or decision. For financial calculations, compare the estimate with the actual terms supplied by a lender, employer, bank or other provider. For documents and images, keep the original file and inspect the processed copy before sharing it.

Use the related UniConvertHub tool

The interactive Image Compression Guide tool is designed to make the calculation or file task quick to test in a browser. You can also browse the full guide library for related explanations.