How to Reduce Image File Size
Two different operations get called this. Most of the time you want both, in a particular order.
Checked August 6, 2026
The short answer
There are two ways to make an image file smaller and they are not the same thing. Compressing keeps the picture at its full pixel size and spends fewer bytes describing it. Resizing reduces the pixel size itself. If your file is too big, resize first, down to whatever it will actually be displayed at, then compress. That order is most of the saving.
Which operation you need
| The problem | Do this | What usually happens |
|---|---|---|
| A photo will not attach to an email | Resize, then compress | Several megabytes down to a few hundred kilobytes. |
| A page loads slowly | Resize to the displayed size, then compress | Usually the largest single win available anywhere on the page. |
| An upload form rejects it | Compress to a target size | The pixel size is unchanged, which is what forms usually care about. |
| A screenshot is enormous | Check the format first | A screenshot as PNG is correct. A photograph as PNG is the wrong format, not a size problem. |
The order matters because compressing an image that is four times larger than it needs to be spends all that effort on pixels nobody is ever going to see.
Where the bytes actually are
A photograph straight off a phone is often twelve megapixels and several megabytes, and it will be looked at in a space perhaps a thousand pixels wide. Three quarters of those pixels are being carried around for nothing.
That is why resizing first is the biggest single lever there is. Halving both dimensions removes three quarters of the pixels, and the file falls by roughly the same proportion before any compression has been applied at all.
Then compress, and watch rather than guess
Quality settings are not percentages and the scale is not linear. A number that is right for one picture is wrong for the next. The method that works is to watch the picture and the file size together and stop just before the difference becomes visible, and that point is lower than most people expect.
Busy pictures tolerate far more compression than smooth ones. A photograph of foliage hides its artefacts in the detail. A clear sky, a gradient, or a portrait against a plain wall shows banding and blotching long before the foliage does.
Check the format before blaming the size
A photograph saved as PNG is often five to ten times larger than it needs to be, and compressing a PNG does not fix that, because PNG is lossless by definition. Converting it to JPEG or WebP is the actual fix, and it is a bigger win than any setting.
The reverse holds too. A screenshot of text as JPEG is smaller and visibly worse, and squeezing it further makes it worse still. That one wants to stay PNG.
What not to do
Do not compress the same file repeatedly. Each pass over a lossy file throws away more, and the damage accumulates. Go back to the original and do it once.
Do not enlarge a small file hoping to improve it. Adding pixels adds no detail, and the file gets bigger for nothing at all.
Doing both here
The resizer sets the pixel size and the compressor sets the bytes, and both run on your own machine, so nothing is uploaded. The compressor takes a target size when a form has a limit, or a quality when your eye is the judge, and prints what the file weighed before and after, so the trade is visible rather than assumed.
More guides
GuidesFAQ
- How do I reduce image file size without losing quality?
- Resize it to the size it will actually be displayed at, which loses nothing you would have seen, then compress just to the point before the difference shows. Strictly lossless compression exists and saves far less.
- What is the difference between compressing and resizing?
- Compressing spends fewer bytes on the same number of pixels. Resizing reduces the number of pixels. Most people who want a smaller file want both, and resizing goes first.
- Why is my PNG so large?
- Because PNG is lossless and discards nothing. That is right for screenshots and flat graphics and wrong for photographs, where JPEG or WebP will be a fraction of the size and look the same.
- What size should a photo be for email?
- There is no rule, but resizing so the long edge is around 1600 pixels and then compressing usually takes several megabytes down to a few hundred kilobytes, which attaches without trouble and still looks right on any screen.
- Does compressing an image twice make it smaller?
- A little, and each pass costs quality that never comes back. Go back to the original rather than compressing an export a second time.
- Is compressing images online safe?
- It depends on whether the tool uploads them. This one does not: the work happens in your browser, and the network panel will show you that the file never leaves.
Compress one and watch the number
Set a target size or a quality, and see the before and after. Nothing is uploaded.
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