Compress an image to 40 KB

Forty kilobytes is 320,000 bits. At about one bit per pixel that supports a square of roughly 565 pixels, or a portrait of 530 by 600. This is the first size on the ladder where a face looks properly smooth rather than merely recognisable.

Upload pages sometimes measure with a different rule than your computer does. A file of 49 KB can read as 47.9 KiB, or be counted with extra header bytes, and then fail. A 40 KB file leaves ten kilobytes of room, so no rounding rule can trip it.

Compression likes plain surfaces. A solid shirt and a wall of one colour keep the file small and the face sharp. Fine stripes, checks and lace are the opposite, because every thread is detail the encoder has to describe.

If you can retake the picture, stand facing a window, with the light in front of you rather than behind.

Crop to head and shoulders, set the pixel size the form asks for, compress to 40 KB, then check the result at actual size. That order spends the budget in the right place: on the part of the picture the reviewer will look at.

Softness at 40 KB usually means too many pixels are sharing the bytes. Lower the width in Resize by a fifth and compress again, and the same weight is spread over fewer pixels at a higher quality.

Cropping helps as well. Removing a wide margin of wall or sky changes nothing the reviewer cares about and frees bytes for the face.

Resize before you compress, not after. If you shrink a picture that was already squeezed to 40 KB, the file gets smaller but the damage stays. Doing it in the right order means the compressor sees the final pixels once and chooses the best setting for them.

If the limit is exactly 40 KB, the margin on this page protects you from a rejection.

Resize before you compress, not after. Shrinking a picture that was already squeezed to 40 KB makes the file smaller but keeps the damage. In the right order the compressor sees the final pixels once and picks the best setting for them.