How to convert image MB to kB on PC?

Converting an image from MB to kB means re-saving it so it takes fewer bytes: a little less JPEG quality and, when that is not enough, fewer pixels. Mb2KbSizer handles both. You type the size a form asks for, press Compress image, and the file comes out at or just under that number. Everything runs inside your browser, nothing is uploaded, and the clicks are the same on Windows, Mac, Android and iPhone.

On a Windows PC or Mac

1. Open mb2kb.online in Chrome, Edge, Firefox or Safari. Nothing to install, no sign-in.
2. Add the picture. Drag it onto the panel that reads Drop your image here, click browse your files, or paste a copied image with Ctrl + V (Cmd + V on a Mac). JPG, PNG, WebP, GIF, BMP and AVIF files up to 60 MB are accepted.
3. Set the Target file size. Type the number and pick kB or MB, or click a Quick sizes chip: 20, 50, 100, 150, 200, 250, 300 or 350 kB. The note under the box confirms the output lands at or just under this figure, counting 1 kB as 1,000 bytes.
4. Open Format & dimensions only if you need it. This optional panel holds Output format and Resize. For a plain “under 100 kB” rule leave it closed.
5. Click Compress image. A progress bar appears with the line “Working on your device — nothing is being uploaded.” A phone photo takes a few seconds.
6. Read the result card. It lists Original, Compressed, Saved and Dimensions above a “Size vs target” meter. A green message such as “Done: 97,812 bytes at 82% quality. That is safely under your 100.0 kB limit.” gives the exact byte count. Use the slider or Hold to compare to check sharpness.
7. Click Download. The new size appears on the button and in the file name, for example photo-98kb-mb2kbsizer.jpg.

Need another size? Change the target and press Compress again with these settings. Compress another image clears the page for the next file.

On an Android phone

The page is identical on a phone; only the file picker and the download location differ.

• Open the site in Chrome or Samsung Internet and tap the dashed panel. Android offers its file picker, your gallery app and usually the camera, so you can photograph a document and compress it in one pass.
• A typical phone photo today is roughly 2–8 MB, so Saved often reads 95% or more at targets under 100 kB. That is normal.
• The result lands in your Downloads folder. When a portal asks for the file, pick it through Files or Downloads rather than the gallery, which can be slow to notice new images.
• A weak signal does not slow the compression; data is needed only to load the page, and the work runs on the phone itself.
• Dozens of photos? The bulk image compressor handles up to 200 files with one target and offers Download all as ZIP.

On an iPhone or iPad

Use Safari. Tap the panel, choose a photo from the library, the camera or a file, set the target and press Compress image as above. Safari saves the result to the Files app (Downloads folder by default), where Choose File on any form will find it.

The iPhone-specific wrinkle is HEIC. According to Apple’s support note on HEIF and HEVC (December 2025), the camera’s default High Efficiency setting stores photos as HEIF, seen as a .heic file. Safari 17 and later can open that format, so Mb2KbSizer compresses it directly and returns a JPG, which every portal accepts. Chrome, Edge and Firefox cannot decode HEIC (caniuse.com, October 2026); there the tool stops with “Your browser cannot open HEIC photos. Open this page in Safari, or set your iPhone camera to “Most Compatible” (JPG) and try again.”

To switch permanently, open Settings > Camera > Formats and tap Most Compatible; new photos are then captured as JPEG. Apple also notes that photos sent by Mail, Messages or AirDrop may be converted to JPEG automatically when the receiving device cannot read HEIF.

Compressing a PDF instead

Certificates, mark sheets and signed forms usually have to be PDFs. The PDF compressor follows the same pattern:

1. Drop the file on Drop your PDF here or tap browse your files. One PDF at a time, up to 100 MB, any number of pages. A password-protected file is refused with “This PDF is password-protected. Remove the password first, then try again.”
2. Enter the Target file size in kB, MB or % of original, or tap a quick chip.
3. For a scan or a signed form, tick Convert to black & white. Grayscale pages hold far less data.
4. Press Compress PDF; large files can take a minute.

The result message says which of two methods ran. If a lossless clean-up was enough, it reads “using lossless optimisation — text stays selectable”. If the pages had to be re-rendered, it gives the dpi used (up to 150, lower only when necessary); the text then becomes part of an image, so it is no longer selectable or searchable, and links and fillable fields are lost. Page 1 is shown before and after so you can check legibility before pressing Download. The 100 kB PDF preset pre-fills the target.

Hitting an exact size every time

• Type the real limit, not a round guess. If the portal says 50 kB, enter 50. The tool searches quality levels until the output is at or just under that figure, so expect something like 47–49 kB. The 50 kB and 200 kB preset pages have the number filled in already.
• Shrink pixels before you squeeze quality. At small targets, dimensions matter more than the quality setting. A 3.2 MB photo at 4000 × 3000 px typically comes out around 96 kB at about 1200 × 900 px. Mb2KbSizer makes this trade automatically, but you can steer it: set Resize to Fit within width × height and enter a longest side such as 1000 px.
• Use Exact when the form names pixels. A rule like “200 × 230 px, under 20 kB” needs Exact width × height (crops edges). The photo is scaled and centre-cropped, never stretched.
• Pick the format the portal expects. Auto gives JPG for photos and keeps WebP input as WebP, which suits most forms. WebP is worth choosing for your own website: Google’s WebP documentation reports lossy WebP about 25–34% smaller than JPEG at similar quality, but some upload forms still reject it. Choose PNG only for graphics that must keep transparency; PNG is lossless, so it only shrinks through smaller dimensions.
• Transparent areas turn white when a PNG is saved as JPG. For a signature scan that is what most portals want.

Further reading: reduce image size without losing quality and JPEG vs PNG vs WebP.

If the result is blurry or still too big

It looks soft. The target was small for the pixel count, so the tool cut dimensions or used a low quality setting. Check the Dimensions value and the quality percentage in the result message, then either raise the target (if the portal allows) or accept a smaller picture that stays sharp. Judge at normal size with Hold to compare; zooming to 300% exaggerates artefacts that will never show on the portal.

An amber warning says the target was not reached. The message begins “We could not get this image under … with your settings.” It almost always means Resize is holding dimensions too large for the size, for example a 6000 × 4000 px scan with a 20 kB target. Open Format & dimensions, switch to Fit within, enter something like 800 px, and compress again.

Text or line art looks smudged. JPEG adds halos around sharp edges. Try WebP, or PNG with smaller dimensions.

The result equals the original. You will have seen “Good news: your image is already …”. The file was under the target to begin with, so the original is offered untouched.

A PDF will not go small enough. Tick Convert to black & white, raise the target, or split the document and compress each part. For exam and job portals, compress images for government forms lists the common pitfalls.