Resize Photo to KB

about this tool

Bring a photo to the size a form asks for

Many online forms, exam and job applications above all, set a size for the photo and the signature — between 20 and 50 KB, under 100 KB, 200 × 230 pixels — and refuse anything else. An ordinary compressor asks for a quality and leaves you to guess what size comes out. This works the other way round: say the size, and it finds the best picture that fits.

1. Pick what the form wants: photo 20–50 KB, signature 10–20 KB, one of the plain limits from 20 to 500 KB, or my own size to type the range and the pixels from your form — 50, 50 KB, 1 MB and 20-50 all work.
2. Choose the photo, or a photo of your signature in dark ink on white paper, cropped close round it first with image resize so it does not shrink to a strip.
3. Download the JPG. The page shows its size in KB and in bytes, its pixel size, and the quality it settled on. The file is marked 200 dpi, which some forms' instructions ask for; it changes no pixels and no bytes.

The two ready-made sizes — a 200 × 230 pixel photo at 20 to 50 KB and a 140 × 60 pixel signature at 10 to 20 KB — are what many exam and job forms ask for, but rules change from form to form and year to year, so check yours and use my own size when it differs.

How it finds the size

The page encodes the picture as a JPEG and searches the quality, halving the gap each time, for the highest quality whose file is no bigger than the limit. That takes about ten encodes for each pixel size it tries, and a moment.

When the form sets no pixel size, a large phone photo is first brought down to a sensible size, and if the quality that fits is still poor, the picture is made smaller again instead — a smaller sharp picture beats a large blocky one, and a form never needs twelve megapixels. When the form does set the pixel size, that size is kept exactly; if the shape differs from your photo, crop to fill trims it to fit — evenly from the sides, but more from the bottom than the top, so a face keeps its forehead — and fit inside keeps everything and fills the rest with white.

When even the best quality is smaller than the least size the form accepts — common with a small signature — the file is padded with an empty JPEG comment, which every viewer skips, to half a KB past the least, for a form that checks "more than" rather than "at least". The picture is exactly the same, only the file is bigger, and the page says how much was added.

Counting KB the strict way

Some forms count a KB as 1,000 bytes and some as 1,024, and they rarely say which. So the page counts the strict way at both ends: the most as 1,000 bytes a KB and the least as 1,024. A file made for "20 to 50 KB" is at least 20,480 bytes and at most 50,000, and passes either way. The page shows the size both ways too: a phone or a Mac counts 1,000 bytes a KB and shows 50 KB, Windows counts 1,024 and shows 48.8.

Private

The photo never leaves your device: it is opened, resized and encoded by your browser, and the JPG it makes carries no camera details or location, since a re-encoded picture keeps none of the original's metadata. To shrink many photos at once by quality instead, use the image compressor; to crop by hand or to a social-media size, image resize; and to turn an iPhone's HEIC photo into a JPG first, the image converter.

questions

How do I make a photo between 20 and 50 KB?

Pick photo 20–50 KB, then choose the photo. The page crops it to 200 × 230 pixels and searches the JPEG quality for the best picture that still fits under 50 KB; if even the best quality comes out under 20 KB, it pads the file to just over 20 KB without changing the picture. Then download the JPG. For a different range, choose my own size and type what your form says.

Why is my file a little under the limit, not exactly on it?

Forms disagree about what a KB is: some count 1,000 bytes and some 1,024. The page counts the strict way at both ends — the most as 1,000 bytes a KB and the least as 1,024 — so the file passes either way. A 50 KB limit gives a file of at most 50,000 bytes, which a phone or a Mac shows as 50 KB and Windows as 48.8 KB; the page shows both.

How can a file be made bigger without changing the picture?

A JPEG can carry comments that every viewer skips. When a picture at the best quality is still smaller than the least size the form accepts, the page adds an empty comment just after the file’s header, making up the bytes it is short and half a KB more, for a form that wants more than the least rather than at least. The picture is exactly the same; only the file is bigger. That is better than making the picture larger, which only blurs it.

What if the photo is still too big?

When no pixel size is set, the page makes the picture smaller rather than dropping the quality so far that it turns to blocks, and says so. When the form fixes the pixel size, the size stays and the quality goes down as far as it must; if even the lowest quality is too big, the page says how big it is, so you can allow more KB or fewer pixels.

Does it crop my photo?

Only when the form asks for a pixel size with a different shape from your photo. Crop to fill trims it to fit — evenly from the sides, and more from the bottom than the top, so a face keeps its forehead; fit inside keeps all of it and fills the rest with white. With no pixel size, or only a width or a height, the photo keeps its own shape.

Is my photo uploaded?

No. The photo is opened, resized and encoded by your browser on your device, and nothing is sent anywhere. The JPG it makes has no camera details or location in it, since a re-encoded picture carries none of the original’s metadata.