How much smaller will my images get?
1 min read · Last updated June 2026
It depends almost entirely on where your images came from. There is no single number, because the savings on a fresh export from a design tool are very different from the savings on an image that was already squeezed down before you uploaded it.
What drives the savings
- Large savings: images that were never optimized - exports straight from a design tool, screenshots, and photos straight off a phone or camera. These usually have a lot of room to shrink.
- Small savings: images that were already compressed before you uploaded them, such as a photo a previous plugin already optimized, or a small graphic that is close to as small as it sensibly gets. There is little left to remove.
If you store photos as PNG, converting the opaque ones to JPEG can shrink them further - see Why isn't my PNG converting to JPEG?. And serving WebP and AVIF (which SlashImage does by default) shrinks things further again for visitors, because those formats are smaller than the JPEG or PNG even after it is optimized.
See your real numbers
Rather than guess, look at the actual savings SlashImage reports:
- The SlashImage column in your Media Library shows Reduced by X% for each optimized image, or Already optimal when an image was already about as small as it gets.
- The Bulk Optimize page shows your total savings so far across the whole library.
See What does the SlashImage column show? and How do I optimize images I already uploaded?.