How to Reduce an Image to 100 KB, 200 KB or 1 MB: Measured Settings

An upload form says the image must be under 100 KB, or 200 KB, or 1 MB. Most advice for this tells you to drag a quality slider until the number gets small enough. That works for a photo that is only slightly too big. It fails when the file is far over the limit, and it never tells you how much quality you have to give up before you get there.

So I measured it. I took one full-size text screenshot and one large photo, and for each I recorded the file size at different qualities and widths, then searched for the quality that lands just under each common limit. The tables below are those results. They let you choose a width and a quality in one try instead of guessing.

What I Tested, and What I Did Not

• Screenshot: a capture of a long Wikipedia article at a 1470 by 956 window on a 2x display setting, which is 2940 by 1912 pixels. It is mostly text, so it is a hard case for JPEG. As a PNG it was 989,464 bytes.
• Photo: a 4032 by 3024 landscape picture, about the size of a phone camera shot, saved as a JPEG of 2,201,303 bytes. It is a stand-in made from a large Apple landscape image on my Mac, not a picture from a camera, so a noisy real photo with more fine grain will land somewhat larger at the same settings.
• Tools: ImageMagick for the size measurements and the quality search. File sizes depend on the encoder, so another program will be a few percent off but follow the same pattern.
• Not measured: how the results look on your screen. I checked one screenshot crop by eye, described below, and I did not judge the photo results visually.

Finding 1: Converting to JPG Does Not Always Shrink the File

The first surprise was that the usual first move, convert the PNG to a JPG, made the screenshot bigger at high quality:

Flat colors and sharp text are what PNG compresses well, so a text screenshot gains little from JPEG until the quality is low. Notice also how slowly the size falls. Going from quality 90 to quality 30 cuts the file by about two thirds, and it is still 292,014 bytes, nearly three times a 100 KB limit. This is the core problem with the quality slider alone: at full size, it runs out of room before it reaches a small target. If you are choosing between formats in general, PNG vs JPG vs WebP: Which Format Should You Use covers the tradeoffs, and Why PNG Files Get Bigger After Re-Encoding explains why sizes can grow.

Finding 2: Width Moves the Size More Than Quality Does

Here is the same screenshot at smaller widths. Each width was scaled down and saved at two qualities:

Halving the width removes about three quarters of the pixels, and the file dropped by roughly the same proportion at quality 70, from 474,422 bytes to 181,242. Lowering quality from 85 to 70 at one width only trims about a quarter. Width is the big lever and quality is the fine adjustment.

The Lookup Table: Which Width and Quality Hit Each Limit

For each target I searched for the highest JPEG quality that stays at or under the limit, at three widths. The cap of the search was quality 95, so a value of 95 means the limit is met with room to spare. "Not reachable" means even the lowest quality I tried (5) stayed over the limit.

Screenshot (text, 2940 by 1912 at full size)

Photo (4032 by 3024 at full size)

Read it by finding your limit in the left column and moving right until the quality is somewhere between about 60 and 90. That is the width to use. For a 100 KB limit, the screenshot needs to be around 1000 pixels wide to keep a quality of 70, and the photo is the same at 1000 pixels. For 1 MB, the photo only needs a quality of 70 at full size, so no resizing is needed at all.

Does a Very Low Quality Look Bad?

A low number does not always look as bad as it sounds. I took the 100 KB case for the screenshot, the full-size file at quality 26, and compared a 600 by 300 pixel crop of body text against the original PNG at 100 percent zoom. The text was still sharp and readable, and I saw no visible difference between the two at that zoom. That is why the table shows quality 26 as a workable result for a text screenshot, and it is the reason I would not rule out a low quality for text without checking.

The other route, shrinking the screenshot to 1000 pixels wide and then stretching it back up to compare, looked soft, but that comparison is unfair, because you would normally view the smaller file at its own size. This is the real tradeoff:

• Keep the pixels, lower the quality if the image will be zoomed or printed, or if the form insists on a minimum width or height.
• Lower the pixels, keep the quality if it will only be shown at a small size, such as a thumbnail, a profile picture or a form preview.

I did not judge the photo results by eye, so for a photo, look at the output yourself before submitting it. Skies, skin and gradients show banding and blocks sooner than text does. The general rules for spotting a setting that is too low are in Image Compression Quality Settings Explained With File Sizes.

Three Ways to Do It

1. Mac Preview

• Open the image in Preview and choose Tools, Adjust Size. Set the width in pixels with the proportions locked.
• Choose File, Export, set Format to JPEG, and drag the Quality slider. The dialog shows the estimated file size, so you can stop when it is under your limit.

2. Windows

• Open the image in Paint and use Resize and Skew to set the width by percentage or pixels with the aspect ratio kept.
• Use File, Save as, JPEG picture. Paint does not give you a quality slider, so you control the size mostly with the width. Check the file size in File Explorer and shrink again if it is still too big.

3. Command line, for an exact target

If you have ImageMagick, it can search for the quality itself. This writes the largest JPEG it can that stays under 100 KB, after shrinking to 1470 pixels wide:

magick input.png -resize 1470x -define jpeg:extent=100kb output.jpg

On my screenshot this gave a 96,445 byte file at quality 24. I also ran it at full size with no resize, and it reached 83,442 bytes only by dropping to quality 2, which is a reminder to set the width first. On the photo, a 2000 pixel wide copy with a 200 KB target came out at 195,641 bytes and quality 38.

Where PasteDownloadApp Fits, and Where It Does Not

PasteDownloadApp does one conversion job. It turns the image on your clipboard into a PNG, JPEG or WebP file in your browser, without uploading it. It does not have a size target, a resize option or a quality slider. By its source, JPEG and WebP are written at a fixed quality of 0.92 at the image's original dimensions, so the output from a full-size screenshot will land near the quality 90 to 95 rows in the first table, which is close to 1 MB for my screenshot. I measured 934,922 bytes at quality 92 and full size.

The practical use is getting a clean file out of the clipboard in the first place. Paste the screenshot, download it as JPEG, then reduce its width with one of the three methods above. If the file is going into an email, How to Turn a Pasted Screenshot Into an Email Attachment covers the next step, and the batch options in How to Convert Multiple Screenshots Fast help when there are many files.

A Few Things That Trip People Up

• Kilobytes and mebibytes: some forms count 1 KB as 1,000 bytes and some as 1,024. I used 1,024 for the limits above (100 KB is 102,400 bytes). If a form is strict, aim 5 to 10 percent under the limit.
• Transparency: JPEG has no transparent pixels, so a transparent PNG gets a solid background. The tool paints white behind it.
• Pixel size requirements: a form that asks for a size in KB sometimes also asks for exact dimensions. Set the dimensions first, then tune the quality for the size.
• Re-saving: each time a JPEG is opened and saved again it loses a little more detail. Work from the original and save once.
• Metadata: a phone photo carries location and camera data that adds a little to the size. For a 100 KB target it rarely matters, but you may want it removed for privacy anyway.

Sources and Method

• All sizes are measurements I made on October 25, 2026, with ImageMagick 7.1.2 on macOS. The screenshot was captured from a public Wikipedia page with a headless Chrome window at a 2x scale factor. The photo is a 4032 by 3024 crop of a landscape image bundled with macOS, used only for measurement.
• The quality search was a binary search between 5 and 95, and recorded the highest quality at or under each limit.
• Quality 92 and the fixed output settings of PasteDownloadApp come from reading the tool's own code. The 934,922 byte figure is an ImageMagick measurement at quality 92, and a browser's encoder can differ by a few percent.
• Not tested: Windows Paint, macOS Preview export estimates and the visual quality of the photo results. Those steps come from how the programs are laid out and are worth checking on your own file.

Frequently Asked Questions

How do I reduce an image to under 100 KB?

Shrink the width first, then lower the JPEG quality. In my test, a 2940 by 1912 screenshot could not reach 100 KB at any quality worth using, but at 1470 pixels wide it fit at quality 26, and at 1000 pixels wide it fit at quality 70.

Does converting PNG to JPG always make the file smaller?

No. A text-heavy 2940 by 1912 screenshot was 989,464 bytes as PNG and 1,122,123 bytes as JPEG at quality 95. JPEG only wins once the quality is lowered or the image is made smaller.

What is the lowest JPEG quality that still looks fine?

There is no single number, because it depends on the image. On a text screenshot, quality 26 at full size still read cleanly at 100 percent zoom in my check, while a photo needs more care. Judge by looking at the result at the size it will be shown.

Can I set a target file size in PasteDownloadApp?

No. The tool converts at its original dimensions with a fixed JPEG or WebP quality of 0.92 and has no size target. It is useful for turning a clipboard image into a file, and you then shrink the file with the steps in this guide.

How can I hit an exact size from the command line?

With ImageMagick, add -define jpeg:extent=100kb to a convert command. In my test it produced a 96,445 byte file from a 1470 pixel wide screenshot at quality 24.

Related Guides

Image Compression Quality Settings Explained, With Real File Sizes What a JPEG or WebP quality number actually changes, shown with real before-and-after file sizes. PNG vs JPG vs WebP: Real File Sizes Compared PNG vs JPG vs WebP for quality, transparency, and file size, backed by real measured results, not general claims. How to Turn a Pasted Screenshot Into an Email Attachment Gmail and Outlook can paste an image straight into the message body, but that is not the same as an attachment. Here is how to turn a clipboard image into a real file first.