Check Image File Size
See exactly how many kilobytes or megabytes an image takes up, and how efficiently it is compressed for its pixel size.
- On-device
- No sign-up
- Batch
- Free, no watermark
Drop images on the plate
or paste with Ctrl/⌘ V
Processed on this device
How it works
- 01Drop, choose or paste the images to check.
- 02Read the size, bits per pixel and compression ratio for each file.
- 03Copy the exact byte count or size you need.
Why use this tool
Both KB definitions
Sizes are shown in decimal (1 KB = 1000 bytes) and binary (1 KiB = 1024 bytes) units, so you can match whichever one a form uses.
Compression at a glance
Bits per pixel and the ratio against uncompressed size show whether a file is lean or bloated for its dimensions.
Compare a whole batch
Add up to 200 images to see which files are making a page or an email attachment heavy.
Supported formats
Use cases
Forms with a size cap
A form accepts photos under 50 KB. Check the exact size in both units before uploading, because 50 KB and 50 KiB are not the same number of bytes.
Finding heavy page images
Drop the images from a slow page and sort out which ones have unusually high bits per pixel and need compressing.
Email attachment limits
Check the total size of a set of photos before attaching them, so the message stays under your mail provider’s attachment limit.
Technical details
File size depends on pixel count, format and compression settings. Bits per pixel divides the file size in bits by the number of pixels: a well-compressed web JPG is often around 1–3 bits per pixel, while a PNG photo can be 10 or more. The compression ratio compares the file with the uncompressed size, which is 24 bits per pixel for RGB or 32 with transparency. A ratio of 10:1 means the file is a tenth of its raw size.
The decimal and binary figures differ by about 2.4% at the KB level and almost 5% at the MB level, which is enough to push a file over a strict limit. When a form states a maximum, compare against the exact byte count and leave a little headroom. If a file is over a limit, Compress to Exact File Size finds the highest quality that fits under the target you set.
Your files stay with you
This tool runs entirely inside your browser using Web Workers and WebAssembly. Your images are never uploaded, never stored on a server and never used to train AI. Close the tab and they’re gone. Learn more
Frequently asked questions
Is 1 MB 1000 KB or 1024 KB?
Both conventions are in use. Decimal units count 1 MB as 1,000,000 bytes, which macOS and iOS use. Binary units count 1 MiB as 1,048,576 bytes, which Windows Explorer shows labeled as MB. The checker shows both, so you can match the number a form or app displays.
Why does my upload say the image is too large when it looks under the limit?
The site may measure in a different unit than your computer, or count the size after encoding. A file shown as 49 KB in binary units is about 50.2 KB in decimal. Check the exact byte count here and leave a small margin below the stated limit.
What is a good bits-per-pixel value?
For photos on the web, roughly 1 to 3 bits per pixel in JPG or WebP usually looks good. Far higher values suggest the file could be compressed further. Screenshots in PNG vary more, because flat colors compress very well and detailed photos saved as PNG do not.
Does the checker change or upload my files?
Neither. It only reads the files in your browser tab and produces a report, so no new files are created and nothing is sent to a server. Remove the images or close the tab when you are done.
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