How many KB are in 1 MB?
There are two conventions, and both are in use. In the binary one, 1 KB is 1,024 bytes and 1 MB is 1,024 KB (1,048,576 bytes); Windows File Explorer and many upload forms count this way. In the decimal one, 1 KB is 1,000 bytes and 1 MB is 1,000 KB; macOS Finder and storage makers use it. The gap is under 5%, so it only matters when a file sits right at a limit.
| Megabytes | KB (1 MB = 1,024 KB) | KB (1 MB = 1,000 KB) |
|---|---|---|
| 0.5 MB | 512 KB | 500 KB |
| 1 MB | 1,024 KB | 1,000 KB |
| 2 MB | 2,048 KB | 2,000 KB |
| 3 MB | 3,072 KB | 3,000 KB |
| 5 MB | 5,120 KB | 5,000 KB |
| 10 MB | 10,240 KB | 10,000 KB |
What actually makes a photo smaller in KB?
A photo's file size comes from three things: how many pixels it has, how much detail those pixels hold, and how strongly it is compressed. You control two of them, plus a small bonus:
- Pixel dimensions first. Phone cameras commonly save 12 megapixels (4,032 × 3,024) or more. Halving the width and height keeps a quarter of the pixels and cuts the file by roughly three-quarters, with no visible loss on a phone or laptop screen.
- JPEG quality second. Cameras save at a high quality. Re-saving at 70–80 usually halves the file again, with no difference you can see at normal size.
- Metadata last. Camera data, GPS location and the embedded preview add a few KB to a few tens of KB; removing them costs nothing.
Quality alone has a floor. Squeezing a full 12-megapixel photo into 100 KB would leave less than 0.1 bit per pixel, and the result would be blocky. The guide to compressing an image to a specific size explains the math.
How do I reduce a 3 MB photo to under 500 KB, 200 KB or 100 KB?
Typical results for a 4:3 phone photo saved as JPEG (busy scenes land at the top of each range)
| Goal | Resize the long edge to | JPEG quality | Typical result |
|---|---|---|---|
| Under 1 MB | 3,000 px | 70–75 | 600–950 KB |
| Under 500 KB | 2,048 px | 75 | 300–480 KB |
| Under 200 KB | 1,280 px | 70–75 | 100–190 KB |
| Under 100 KB | 1,000 px | 65–70 | 55–100 KB |
| Under 50 KB | 700 px | 60–70 | 30–50 KB |
| Under 20 KB | 450 px | 50–60 | 12–20 KB |
Down to about 1,280 px, the photo still looks sharp full screen on a phone. The smaller rows suit thumbnails, ID photos and form uploads, where the site decides the size for you.
How do I convert a photo from MB to KB, step by step?
- Open the compressor at the size you need: under 500 KB, under 200 KB, under 100 KB, or the compressor with Target size set to any number.
- Drop the photo. It works in Chrome, Edge, Firefox and Safari, on a computer, an iPhone or an Android phone; HEIC photos from an iPhone open in Safari.
- Keep Same as original, or choose JPG if the site only takes JPEG. HEIC photos become JPG either way.
- Compress. The tool finds the highest quality that fits, and scales the photo down step by step only if quality alone cannot get there.
- Check the new size and dimensions shown with the result, then download.
How do I check a photo's size in KB?
On Windows, right-click the file and choose Properties; on a Mac, select it and press Command-I for Get Info. The Details tab on Windows and the More Info section on a Mac also show the pixel dimensions. Windows reports sizes in 1,024-based units and macOS in 1,000-based ones, so the same file shows slightly different numbers. The guide to checking image file size and dimensions covers phones too.