OneTaskBy Tim King · Updated
CRC32 Calculator
CRC-32C and Adler-32 Checksums of Text or Hex Bytes, in Hex or Decimal
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How the CRC32 Calculator works
Type text or paste hex bytes into this CRC32 calculator to get the CRC-32 checksum used by ZIP, PNG and gzip, the CRC-32C variant used by iSCSI, ext4 and many databases, and the Adler-32 checksum from zlib. Results appear in hex and decimal as you type.
What the CRC32 calculator computes
A cyclic redundancy check treats the data as one very long binary number and divides it by a fixed polynomial; the remainder is the checksum. CRC-32 uses the polynomial 0x04C11DB7 (processed in its reversed form 0xEDB88320), starts at all ones and flips the result. CRC-32C uses the Castagnoli polynomial, which catches more error patterns and has its own CPU instruction on modern processors.
Checking your implementation
The standard check value is the checksum of the ASCII text 123456789. CRC-32 gives cbf43926 and
CRC-32C gives e3069283. If your code produces something else, the usual causes are a missing final
XOR, the wrong starting value, or bits processed in the wrong order.
Checksums are not security
A CRC detects accidental corruption — a flipped bit on a disk or a dropped byte on a wire. It is easy to forge on purpose: anyone can change a file and adjust four bytes to keep the CRC the same. To prove a file has not been tampered with, use SHA-256, and to prove who sent it, use an HMAC or a signature.
FAQ
Why do two tools give different CRC32 values?
There are dozens of CRC-32 variants with different polynomials, starting values and bit orders. This page uses the ISO-HDLC variant from ZIP and PNG, plus CRC-32C. Also check the input: a trailing newline or a different text encoding changes the bytes and so the result.
How do I enter binary data?
Choose Hex bytes and paste the data as hexadecimal. Spaces, commas, colons and 0x prefixes are
ignored, so output from most hex dump tools can be pasted as is. The byte count confirms how much data
was read.
What is Adler-32 used for?
Adler-32 is the checksum inside zlib and PNG's compressed data streams. It is faster than CRC-32 but weaker on short inputs. It is shown here because it often needs checking alongside CRC-32 when debugging compressed files.
See also: all Security & Identifiers tools, Dev Utilities, Formatters & Validators, Data & Encoding, SEO, Accessibility, AI.
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