Compare the size of two photos

Pixels and kilobytes are different sizes

A 4000 × 3000 photo has twelve million pixels. Saved as a high-quality JPEG it might take 4 MB; saved at a lower quality the same twelve million pixels might take 800 KB. Pixel dimensions decide how large a picture can be shown or printed sharply. File size decides how long it takes to send and whether an upload form accepts it. Changing one does not have to change the other, so the readout keeps them apart.

Bytes per pixel ties them together: the file size divided by the number of pixels. A low figure means heavy compression or very plain content; a high one means light compression, lots of fine detail, or a lossless format such as PNG.

Scale factors without the guesswork

The readout gives B's width and height as a multiple of A's, and the area ratio. A photo resized to half its width has a quarter of the pixels — the area ratio says ×0.25 even though the linear ratio says ×0.5. When the two aspect ratios differ, the photo was cropped as well as resized; the alignment note in the workspace says where the crop sits.

The drawing in the panel puts both photos on one canvas at their true relative size, the smaller one outlined over the larger, with a dashed 1080 × 1080 px square for reference — the size Instagram's help centre gives for photos uploaded at their best quality.

This compares; it does not resize

Some people searching for photo size want to make a picture smaller. This page will not change your file. It tells you exactly how two files differ in size, so you can check what an app, an editor or a messaging service did — and for whether a file meets an exam or form limit, the compressed-image check has editable targets.