About the CRC Checksum Calculator
This tool calculates nine classic checksums at once: CRC-32, CRC-32C, three CRC-16 variants, CRC-16/MODBUS, CRC-8, Adler-32 and Fletcher-16. Type text, paste hex bytes or pick a file, and every result updates immediately, in hex and in decimal. Checksums are short numbers that catch accidental changes such as a flipped bit in a download or a serial-line frame. They are not security hashes, so do not use them to prove a file is safe. Everything is worked out in your browser and nothing is uploaded.
Updated September 2026
How to use the CRC Checksum Calculator
- 1Choose Text, Hex bytes or File.
- 2Type, paste or pick what you want to check. Results appear straight away.
- 3Switch between upper and lower case hex if your other tool uses one style.
- 4Paste a checksum from another source into the compare box to see which algorithm it matches.
- 5Press Copy next to the result you need.
What checksums are for
A checksum is a small number computed from a block of data. Send the data together with its checksum, and the receiver can compute the number again: if the two differ, something changed on the way. CRCs are popular because they are fast, need almost no memory and are very good at finding the burst errors that happen on cables, disks and radio links.
They were designed against noise, not against attackers. Someone who wants to change a file and keep its CRC the same can do that in seconds, so never use one as a signature.
Which algorithm should I pick?
- CRC-32: the default when someone just says CRC32. Use it for ZIP, PNG and gzip checks.
- CRC-32C: storage and network protocols such as iSCSI and SCTP.
- CRC-16/MODBUS: industrial devices, sensors and PLCs. Modbus sends the result low byte first.
- CRC-16/XMODEM and CCITT-FALSE: serial protocols, Bluetooth and many embedded systems.
- Adler-32: zlib streams. Quicker than CRC-32 but weaker on short inputs.
- Fletcher-16: a simple two-sum check used in some network protocols.
Tips for matching a result
If your number does not match, the usual causes are a different variant, different line endings, a trailing newline or a different text encoding. Try hex mode to rule out encoding problems, then paste the expected value into the compare box: a match against another algorithm tells you which variant the other system uses.
A value that begins with zeros keeps them here (00000000 is a valid CRC-32), and the compare box ignores leading zeros and a 0x prefix.
On a phone or computer
The page works the same on both. On a phone, pick a file from your storage; it is read in place and never sent anywhere. A few hundred megabytes is fine on a computer, while phones can run out of memory on very big files. For stronger file fingerprints use the SHA-256 Hash Generator, and for text encoding the Base64 Encoder & Decoder.
Features
- Nine checksums in one view: CRC-32, CRC-32C, CRC-16/ARC, CRC-16/CCITT-FALSE, CRC-16/XMODEM, CRC-16/MODBUS, CRC-8, Adler-32, Fletcher-16
- Text is read as UTF-8 exactly as typed, including spaces and line breaks
- Hex input accepts spaces, commas, colons and 0x prefixes
- Works on files of any type, read on your device
- Compare box tells you which algorithm matches
- Checked against the standard test value for the text 123456789
Frequently asked questions
What is a CRC32 checksum?
CRC-32 is a 32-bit number worked out from the bytes of a file or message using polynomial division. The same bytes always give the same number, and almost any accidental change gives a different one. ZIP, PNG, gzip and Ethernet all use it to detect damaged data.
Is CRC32 safe for checking downloads?
It catches accidental corruption well, but it is easy to forge on purpose, so it cannot prove a file is authentic. For that, compare a SHA-256 value with the Hash Generator.
Why does my CRC-16 not match another tool?
There is no single CRC-16. ARC, CCITT-FALSE, XMODEM and MODBUS use different start values, polynomials and bit orders. Paste the expected value into the compare box and see which one matches, then use that variant.
What is the difference between CRC-32 and CRC-32C?
They use different polynomials. CRC-32 (IEEE 802.3) is used by ZIP and PNG. CRC-32C (Castagnoli) is used by iSCSI, ext4 and many storage systems, and has a hardware instruction on modern processors.
How is text turned into bytes?
Text is converted to UTF-8 first, so a letter like é counts as two bytes. Line breaks count too, so a file saved with Windows line endings gives a different result than one with Unix line endings. If you want exact control, use the hex bytes mode.
Is my file uploaded?
No. The file is read into memory on your device and the checksums are calculated there. Very large files may fail on phones with little memory.