What a portal actually measures
An upload form sees bytes, not a picture. It reads the length of the file, looks at the first few bytes to decide what it is, and sometimes reads the pixel size and the DPI from the header. This page reads the same things, the same way, and prints them before you change anything.
- Size in exact bytes, in KB (÷ 1,024), in kB (÷ 1,000) and in MB.
- The real format from the magic bytes, and whether the extension matches it.
- Pixels, megapixels and aspect; the DPI header and the printed size it implies.
- For JPEG: baseline or progressive, colour (including CMYK, which many portals refuse), chroma subsampling and an estimated quality.
- For PNG: bit depth, colour type, palette size and interlacing. Animation, if any: frames and duration.
- Every metadata block and its bytes, with GPS flagged as Location.
TIFF, AVIF and HEIC pixels need a decoder.
Their pixel sizes are not in a simple header. This page asks the browser to decode them; where the browser cannot, the pixel line says so rather than guessing.
Questions people arrive with
- Why does Windows show a different KB from this page?
- Windows Explorer divides by 1,024 and rounds up to the next whole kilobyte, so a 20,481-byte file shows as 21 KB there. This page prints the exact bytes and both readings — divided by 1,024 (KB) and by 1,000 (kB) — so you can compare with whichever the form uses.
- My file is called .jpg. Why does it say PNG?
- Because the format is read from the file's first bytes, not from its name. Renamed files are common, and some portals check the real type. Re-save it as the format the form wants; the compressor on this site does that and names the file correctly.
- What is the estimated JPEG quality?
- An estimate on the common IJG 1–100 scale, worked out from the file's luminance quantisation table. Encoders that use their own scales report different numbers for the same table, so treat it as a guide.
- What does the DPI line mean?
- It is the density written in the header — JFIF, EXIF or a PNG pHYs chunk — and the printed size it implies for these pixels. It changes nothing on screen. Some forms ask for one; the photo resizer in KB writes it.
- Does checking change the file?
- No. Nothing is re-encoded and nothing is written; the file is only read, on this device. "Make it fit this spec" opens the tuner with a copy, and the original stays as it is.
Elsewhere on this site
- Photo size in KB for formsMake a photograph meet a spec, then check it.
- Remove metadata from photoTake the blocks listed here out without re-encoding.
- Compress image to KBBring a file under a cap at the same pixels.