How to Compress an Image to 100 KB (or Any Target Size)

Step 0: Read the requirements carefully

Before touching the image, note exactly what the upload asks for. Most portals specify some mix of the following:

• Maximum (and sometimes minimum) file size, in KB or MB.
• Exact dimensions in pixels, or an aspect ratio.
• File format, usually JPEG (also written JPG).
• Content rules, such as a plain background or a visible face.

If the portal gives exact dimensions, use them exactly. If it gives only a size limit, you have freedom — and that freedom is what makes the next steps work.

Step 1: Crop to what you actually need

Crop away empty background first. Every pixel you remove is a pixel you do not have to compress. For a portrait that means framing the head and shoulders; for a document it means cutting to the page edges.

Step 2: Resize the dimensions

Resizing is the biggest lever. A 4000 × 3000 phone photo has far more pixels than any form needs. If no dimensions are required, something around 1000–1600 pixels on the long edge is plenty for viewing on a screen and is much smaller to store. Our guide on resizing and compressing photos explains why this should always come before compression.

Step 3: Save as JPEG and lower the quality in steps

Photos belong in JPEG. A photo saved as PNG is usually much larger, so converting a PNG photo to JPEG is often the quickest win. Then compress gradually:

1. Save at a high quality (for example around 80%) and check the file size.
2. If it is still too big, step the quality down a little at a time — 70%, then 60%.
3. Stop as soon as you are under the limit. Do not compress more than you need to.

Quality numbers mean slightly different things in different apps, so treat them as a guide and judge by the resulting file size and how the image looks.

If it is still too large

• Shrink the dimensions further rather than dropping quality very low. A smaller, cleaner image usually beats a bigger, blocky one.
• Always start from the original each time you retry. Re-compressing an already compressed JPEG stacks up damage.
• Expect busy images to compress less. Detailed backgrounds cost more bytes than plain ones.
• Remove metadata. Camera details and GPS location add to the file and are worth stripping anyway if you are sending the photo to an unknown recipient.

Check the size before you upload

Check the final size in your phone's file manager. Be aware that some systems count 1 KB as 1,000 bytes and others as 1,024, so leave a small margin — aim a few percent under the limit rather than exactly on it. Then open the image and zoom in to confirm faces and text are still readable.

You can do all of these steps on your phone with ResizeKit, our Android app that resizes, compresses, converts and crops images. It works on your device, so your photos are never uploaded — handy when the photo is an ID or a signature.