Resize Image to KB: Pixel Size, KB Limit and DPI

Last updated: September 28, 2026

Three requirements that are really three different things

Upload forms tend to ask for a photo “at most 100 KB, 300 DPI, 35 × 45 mm” as if that were one setting. It is three, and they are independent:

• The size, in pixels or in millimetres at a given DPI. This is the picture itself: how many pixels it has, and what shape it is.
• The file size in KB: how strongly those pixels are compressed. The same 413 × 531 photo can be 40 KB or 400 KB.
• The DPI: a number in the file header that says how large the pixels should print. It changes neither the picture nor the KB.

This tool applies all three in one pass, in that order: crop and resize, compress to the limit, write the DPI.

How the KB limit is met

The photo is saved as a JPEG at the highest quality that still fits under the limit, found by testing qualities between high and low. If you keep the original pixel size and even the lowest quality is too big, the pixel size is reduced step by step until it fits — and the result says so. A size you fixed is never changed behind your back: when the photo cannot fit at that size, you are told, with the number.

One KB is counted as 1000 bytes. Some forms count 1024; counting 1000 keeps you under the limit either way.

Millimetres, pixels and DPI

When a form gives the size in millimetres, the pixels follow from the DPI: 35 × 45 mm is 413 × 531 pixels at 300 DPI and 827 × 1063 at 600 DPI. Choose “Millimetres” and the tool works it out; the DPI calculator does the same arithmetic for any size.

What this tool does not check

Size, file size and DPI are arithmetic, and the tool gets them exactly right. Whether a photo meets an authority’s rules for ID documents — head size, background colour, lighting, expression — is another question, and this tool does not answer it. The form’s own instructions are the reference for those.

Your photo stays with you

An ID or application photo is exactly the kind of picture not to hand to a random website. Everything here happens in your browser. The output is a freshly drawn JPEG, so EXIF data from your phone — location, device, capture time — is not carried into it.

How to resize a photo to a KB limit

1. 1

   Step 1: Add the photo

   Drag it onto the box above or click to choose it. JPG, PNG and WebP work everywhere; HEIC opens in Safari.

2. 2

   Step 2: Set the size

   Keep the original size, or enter the pixels or millimetres the form asks for. For a fixed size, drag the frame to choose what is kept, and zoom in if needed.

3. 3

   Step 3: Set the KB limit and DPI

   Pick the maximum file size from the form, or type your own; choose the DPI it asks for.

4. 4

   Step 4: Prepare and download

   The result card shows the final size in KB, the JPEG quality used and the DPI written into the file, before you download.

Frequently Asked Questions

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