Six ways to say what size you want
Most resizers give you a width field and a percentage box and stop there. Those two cover maybe half of the reasons anyone resizes a picture. The mode buttons are the other four.
| Mode | You give it | Reach for it when |
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| Exact size | A width and a height | A platform has told you the pixels. This is the only mode where the picture's shape and the box's shape can disagree, so it is the only one with a fit setting. |
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| Width | One number | Images for a web page or a blog post, where the column width is fixed and the height is whatever it is. |
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| Height | One number | A row of logos or headshots that have to line up along a shared baseline. |
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| Longest side | One number | A mixed batch of portrait and landscape photos. Every one comes back within the same bounding box, whichever way up it is. |
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| Percent | A proportion | You want it smaller and you do not care exactly how small. Halving is the safest single choice. |
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| File size | A number of KB | An upload form has a limit. This is the mode that answers "must be under 2 MB" directly instead of leaving you to guess at a width. |
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The crop box, and why it is the same control as the numbers
Drag any of the eight handles to change the crop, drag inside it to move it, or drag on a part of the picture outside it to start a new one. Double-click resets it to the whole image. The box has a focus ring and takes the arrow keys too: one pixel a press, ten with Shift held, and hold Alt to resize instead of move.
The live figure inside the box is the crop in source pixels, and the panel on the right is the actual encoded file, not a mock-up. It is re-encoded as you let go of the handle, so the dimensions and the weight beside it are the dimensions and the weight of the thing you are about to download. Most resizers make you export before they tell you either.
Crop is per file and the rest of the settings are shared. In a batch, dragging the crop on one photo leaves the others alone, while a change of width or format applies to all of them. That is nearly always what you want: the size requirement comes from wherever the pictures are going, and the framing is a decision about each individual photograph.
Why big reductions happen in steps
Taking a 5926px photo down to 150px asks the browser to build each output pixel from a block of about forty by forty input pixels. It does not sample that many. It reads a smaller neighbourhood and discards the rest, which is fast, and which throws away fine texture.
So past a reduction of about four times, the scaling here halves the picture repeatedly instead and only makes the last step directly. Every step then stays inside the range the browser's filter actually covers. Below four times it does not step, because it measurably makes no difference: a 4032px phone photo taken to 1200px scored 0.9952 one way and 0.9950 the other against an exact reference, which is a tie.
Stepping is not free on every picture, and the honest version is on the guide, along with the case where it costs a little rather than gains, and the method and dates for all of it.
Resizing is not the same job as compressing
Resizing changes how many pixels there are. Compressing changes how many bytes each pixel costs. Both make the file smaller and they are not interchangeable.
If a picture is going to be shown at 800px wide, sending a 4000px version of it is waste no amount of compression fixes: the browser downloads four million pixels it will never draw. Resize first. If the picture is already the right size on screen and the file is still too heavy, that is a compression problem, and the quality slider here is the lever. The File size mode does both at once, which is why it asks for a maximum width as well as a budget.
What it will not do
It will not put back detail that is not there. Enlarging spreads the information already in the file across more pixels. It does not invent any, and no tool that runs without a model can. There is no upscaling AI here.
It will not keep your metadata. Scaling means decoding to pixels and encoding again, and EXIF, GPS and the camera settings do not survive that. The rotation does, because it is applied to the pixels deliberately.
It will not open a HEIC outside Safari. No browser except Safari can decode the format, and there is no server here to hand the file to instead. On Chrome or Firefox it says so rather than failing quietly, and the HEIC guide has the fix.
It will not rotate or straighten. A photo that needs levelling by two degrees needs a different tool. The rotation a phone records in its EXIF tag is applied on the way in, so files arrive upright, but there is no dial to turn.