Checksum Calculator: CRC32, CRC16, Adler-32, Fletcher
Calculates CRC-32, CRC-32C, three CRC-16 variants, Adler-32, and Fletcher-16/32 for text or a file in one go. Everything runs in your browser and nothing is uploaded. For cryptographic hashes such as MD5 and SHA-256, use the Hash Generator or the File Hash Calculator.
🔒 Runs in your browser · Your data is never sent to a server
Drag and drop files here, or pick them with the button.
How to use
- Type a string into the "Text" field, or drag and drop files into the "Files" box.
- CRC-32, CRC-16, Adler-32, Fletcher, and other checksums are listed.
- If you have an expected value, paste it into "Value to compare (optional)" to see which algorithm matches.
- Use the Copy button to copy any value.
Notes
- CRC and Adler-32 detect accidental errors only and cannot detect deliberate tampering. Use a cryptographic hash such as SHA-256 for that.
- Files are read in 4 MB chunks, so memory use stays low. Each file can be up to 1 GB.
- Text is checksummed as UTF-8 bytes. Different line endings (LF vs CRLF) give different values.
- CRC-16 has many variants. This tool shows ARC, CCITT-FALSE, and XMODEM; compare against the same variant in the other tool.
Glossary
CRC (cyclic redundancy check)
An error-detection method based on the remainder of polynomial division. It is used in networking, ZIP, PNG, and more to detect corrupted data.
Adler-32
A lightweight checksum used inside zlib and PNG. It is fast, but tends to be weak on very short inputs.
Fletcher
A checksum built from two stacked running sums. Fletcher-16 works on 8-bit units and Fletcher-32 on 16-bit units.
FAQ
When should I use CRC-32 instead of SHA-256?
CRC-32 is for quickly catching accidental corruption in transfers or files. It cannot detect deliberate tampering, so use a cryptographic hash such as SHA-256 where security matters.
My CRC-16 value does not match another tool.
CRC-16 has many variants with different polynomials and initial values. This tool shows ARC, CCITT-FALSE, and XMODEM, so compare against the same variant in the other tool.
Why does a text checksum differ from another environment?
Text is checksummed as UTF-8 bytes. A different encoding such as Shift_JIS, or different line endings (LF vs CRLF), changes the value.
Can I checksum large files?
Yes, up to 1 GB per file. The file is read in 4 MB chunks, so it is never loaded into memory all at once, and it is never uploaded.
How does Fletcher-32 handle an odd number of bytes?
It works on 16-bit words, so a single leftover byte is treated as a word padded with zeros. Other implementations may handle this differently.
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