Start with dimensions
A 4000px phone photo rarely needs to stay 4000px wide for an article, profile image or product card. Reducing pixel width often saves more bytes than pushing quality too low.
Choose a maximum width close to the final display size, then compress. This keeps detail where it matters and removes pixels users will not see.
Use quality as a second control
For photos, a quality range around 70 to 85 is often a practical place to compare. Lower values can be useful for thumbnails, but they may introduce visible blocks or soft edges.
For screenshots, logos and text-heavy graphics, test WebP or keep PNG when sharp edges and transparency matter more than file size.
Check results like a user
Open the compressed result at the size where it will appear on the page or in the upload flow. If it looks clean there, tiny differences at 200% zoom are usually not important.
Keep the original file separately if you may need to edit the image again later.