How to Make an Image Smaller Than 100KB (or Any Size) for Upload Forms

You try to upload a photo to an application form, and it's rejected because the file is too big. This guide shows how to make an image smaller than 100KB, 1MB or any other limit in one step. It also explains what decides file size, why "1KB" can mean two different things, and what to check when the photo is of an ID document. The steps are the same on a phone and a computer.

The short answer: set a target and fit it in one step

The easiest way is the browser-based Compress Image to Size tool.

1. Pick a target size: choose 20KB, 50KB, 100KB, 200KB, 300KB, 500KB, 1MB, 2MB, 3MB or 5MB, or type any size in KB or MB under Custom. Use the form's limit as the target and the result won't go over it.
2. Add your photos: drop them in or tap "Choose photos". JPG, PNG, WebP and iPhone HEIC photos all work (up to 50 at a time).
3. Check and save: each photo shows its new size with the exact byte count, such as 98.2KB (98,213 bytes), plus its quality and pixel dimensions. Compare it with the original in "View and compare", then save it. With several photos, "Save all (ZIP)" puts them in one file.

The tool finds the highest JPEG quality that fits and reduces the pixel dimensions only when quality alone isn't enough. Your photos are processed in the browser and never uploaded, and saved images carry no location data.

You can choose how it fits:

• Best quality (the default): keeps quality at 70% or higher and reduces the pixel dimensions instead.
• Keep dimensions: keeps the width and height and lowers the quality to fit. With a small target, faces and text can blur.

Under "Pixel limits", you can also cap the long side or set a minimum short side (such as 480px), which helps when a form asks for something like "at least 480 pixels wide."

Three things that decide an image's file size

An image's file size comes down mainly to three things: pixel dimensions, quality and format.

1. Pixel dimensions (width × height)

A digital image is a grid of tiny colored dots called pixels. The more pixels, the bigger the file. Halve both the width and the height and you're left with a quarter of the pixels, and the file shrinks a lot too. In our tests with this tool, halving the width and height at the same quality left files at roughly a third to a fifth of their original size, depending on the photo.

2. Quality (how hard it's compressed)

JPG keeps files small by throwing away fine detail that's hard to notice, and the quality setting (a percentage) controls how much goes. Lower quality means a smaller file, but push it too far and edges smear, blocky patches appear, and text gets hard to read.

3. Format (JPG, PNG, HEIC, WebP)

For photos you need to upload, JPG is the safe choice (Compress Image to Size also saves JPG by default, and transparent areas in a PNG turn white).

Why phone photos are so large

Phone cameras today shoot at resolutions such as 12 megapixels (4032×3024 pixels), so a single photo is often several megabytes. For a small limit like "under 100KB," lowering the quality usually isn't enough on its own; the pixel dimensions have to come down too. In the examples below, a 4032×3024 photo didn't fit into 100KB at its full size even at the lowest quality, 5%.

An application usually only needs the text on a document or your face to be readable, so you can often reduce the pixel dimensions and still keep the photo looking sharp.

iPhone photos are often HEIC

iPhones usually save photos as HEIC, which some upload forms don't accept. Compress Image to Size reads HEIC directly and saves a JPG. For more on HEIC, see What Is HEIC? How to Convert iPhone Photos to JPG. If you just need a JPG, the HEIC to JPG Converter does the job.

Fix sideways photos first

When you shoot a document lying flat on a desk, your phone can misjudge which way is up and record the photo sideways or upside down. Turn it the right way with the Image Rotator first, then fit it to size (see how to rotate and flip photos).

Upload limits, and is 1KB 1,000 or 1,024 bytes?

Upload forms often set a maximum such as "up to 300KB per file" or "under 5MB," and sometimes a minimum such as "at least 20KB." Rules differ from form to form, so read the instructions.

The tricky part is what "1KB" means. File sizes are counted in bytes, and some systems count 1KB as 1,000 bytes while others count it as 1,024 (figures in the table are bytes).

For example, a 101,000-byte image passes an "under 100KB" check that counts 1,024 bytes per KB, but fails one that counts 1,000. Forms don't always say which they use.

The safe approach is to count maximums as 1KB = 1,000 bytes and minimums as 1KB = 1,024 bytes, which meets the rule either way. Compress Image to Size counts 1KB as 1,000 bytes when keeping under the target (a 100KB target means at most 100,000 bytes). Your computer or phone may show a slightly different size for the same file because of the difference in counting, so when you're close to a limit, go by the byte count the tool shows. For more on the units, see Data Size Units Explained.

Tips for photos of ID documents

With a driver's license or other ID, what matters most is that your name, address, numbers and face are clearly readable. Compress too far and the text can blur beyond reading.

• When you shoot: use good light, keep the photo in focus, and watch for glare that washes out the text. Follow any instructions such as including all four corners.
• Crop to the document: a desk or background around the card uses up file size. Crop to the document first (keeping all four corners) and the text stays larger at the same file size. Use the Image Cropper (iPhone HEIC photos work as they are) or Crop in the iPhone Photos app or Google Photos.
• Don't go smaller than you need: set the target to the destination's limit. There's no need to go lower.
• Check at 100%: before saving, tap "Show compressed at 100%" in "View and compare" to see the image at its actual size and make sure the text is readable. If it isn't, raise the target or crop to the document.

If your ID shows a sensitive number, such as a national identification number, send that side only when the recipient asks for it.

Japan's My Number Card: online photo rules

This part applies only to Japan's My Number Card. As of October 2026, the official My Number Card site lists these rules for online applications: JPEG format, RGB color (CMYK and similar modes are not accepted), a file size of 20KB to 7MB, and a width and height of 480 to 6000 pixels each. It adds that images edited with image-editing software may not be accepted. For every application method, the photo must have been taken within the last six months and show your face from the front, with no hat, against a plain background.

To make one with Compress Image to Size, set the target below 7MB (for example, 5MB) and keep the format as JPG. Before saving, check that the dimensions shown in the result are between 480 and 6000 pixels for both width and height; if not, set the long or short side under "Pixel limits". The tool changes only the file size and pixel dimensions, never your face or the background, but it can't tell you whether the application will be accepted. Check the official My Number Card site (in Japanese) for the latest rules.

When a photo won't fit the target

When a photo can't reach the target, Compress Image to Size tells you why and what to try next. Common cases:

• A minimum short side stops it from shrinking further: crop to a smaller area. Fewer pixels means a smaller file.
• The target is very small: double-check the destination's limit. A higher target gives a cleaner result.
• You're shrinking a PNG as a PNG: photos stay large as PNG, so save them as JPG. This tool takes PNG files as they are and can save them as JPG.
• "Keep dimensions" left the quality very low: check faces and text in the large view, then switch to "Best quality".
• The original is too small to meet a minimum: the tool never enlarges images, so use a photo with more pixels.

Examples from this tool

These are results from our tests in Chrome on October 18, 2026 (Best quality and a 100KB target unless noted). You can try the same sample photo with "Try a sample photo" in the tool.

• The more fine detail, the more a photo is shrunk: both photos were 4032×3024, yet at 100KB the smooth one kept 1420×1065 pixels while the detailed one went down to 862×646. Fine textures such as leaves or grass need more data for the same number of pixels.
• A smaller target means fewer pixels: at 20KB, the detailed photo came out at 493×370.
• Keep dimensions sacrifices quality: even at the lowest quality, 5%, the photo didn't fit until it was also shrunk slightly. For photos, Best quality usually looks better.

The smooth photo's quality of 70% may look low, but that's because Best quality keeps quality at 70% or higher while keeping as many pixels as it can. Results vary with the photo and the browser.

Summary

File size comes down to pixel dimensions, quality and format. Phone photos have a lot of pixels, so reducing the dimensions, not just the quality, is the quickest way under a limit.

• Fit a set size in one step: Compress Image to Size (HEIC works as is)
• Choose the quality yourself: Image Compressor
• Set exact pixel dimensions: Image Resizer
• Crop to the document: Image Cropper
• Fix sideways or upside-down photos: Image Rotator

For ID documents, check that the text is readable at 100% before you save.

Sources

• My Number Card official site, "顔写真のチェックポイント" (face photo checkpoints, in Japanese): face photo rules (checked October 18, 2026)

This article reflects information as of October 2026. Application requirements can change, so check the destination's instructions or the official website for the latest.