Compress an image to 100 KB

Where the 100 KB limit comes from

A hundred kilobytes is a limit that predates smartphones and has survived because the forms behind it were never rewritten. It appears on government application portals, examination boards, membership registrations, older bank and insurance systems, and a great many things that ask for a photograph of your face.

It is a demanding budget. A phone photograph is fifty to a hundred times this size. The good news is that images at this limit are almost always displayed small — as a form photo, a profile picture, a record in a database — so the resolution you give up is resolution nobody was going to see.

Crop before you compress

This is the single most effective thing you can do at 100 KB and almost nobody does it. Every pixel in the frame costs bytes, including the pixels of the wall behind you and the floor at the bottom of the shot. If the form wants a head-and-shoulders photograph, cropping to head and shoulders before compressing means the whole budget is spent on the part that matters.

A photograph cropped to its subject and then compressed to 100 KB will comfortably beat the same photograph compressed to 100 KB whole, because you have not spent a third of the file describing a beige wall. The crop tool is right there above this text, and the ratio presets cover the shapes forms usually ask for.

What usually goes wrong

Two things. The first is the compress-again loop: taking an already-compressed file and compressing it a second and third time, which bakes the previous round’s artefacts in as though they were detail. Always go back to the original.

The second is fighting for resolution that is doing nothing. At this budget, holding a photograph at 4000 pixels wide leaves roughly a fiftieth of a bit per pixel. There is no encoder setting that makes that look acceptable. Letting the image come down to something like 800 pixels on the long edge and spending the budget there produces a result that people describe as fine rather than as broken.

FileBelow makes that trade automatically and then tells you what it did — the result panel shows the dimensions it chose and what they were before, so nothing is hidden.

Where to go from here

A hundred kilobytes is tight enough that the two-axis search does visible work — the result panel will usually report smaller dimensions than you started with, and why that is the right trade is worth two minutes if the number surprises you.

If this limit came from an application form, it almost certainly came with others: photos and signatures for an application form covers the dimensions, the format and the minimum file size that these forms impose alongside it. Tighter still: 50 KB.

Either side of this: 50 KB if the form is stricter still, 200 KB if it is more forgiving than you first read.

Check for a minimum too

Forms that specify 100 KB quite often also specify a floor — 20 KB, or 50 KB — and reject anything below it. If your destination publishes one, choose it on the Destination tab and FileBelow will show the floor as its own line in the checklist so you can confirm you landed inside the range.