CRC32 calculator
Compute the CRC-32 of text or files — free, instant, in your browser. An error-detecting code, not a cryptographic hash; details below.
the hash appears here — type above or drop a file
Error detection, not cryptography
A CRC is polynomial arithmetic, not a one-way function. CRC-32 exists to answer one question — "did this data get mangled in transit or storage?" — and it answers it well: all single- and double-bit errors caught, all bursts up to 32 bits caught. What it cannot do is resist a person. Fabricating data to hit any chosen CRC-32 is a first-year exercise, so a matching CRC proves nothing about authenticity or tampering. The moment an adversary enters the story, you want SHA-256; the distinction is unpacked in what is a checksum.
Where CRC-32 lives
Inside formats, mostly — you use it daily without seeing it. Every zip archive entry, every PNG chunk, every gzip stream ends in a CRC-32; Ethernet frames carry one; SFV files from the archiving world are lists of them. When you need to match one of those embedded values, or a legacy protocol asks for "the CRC," this page computes it without ceremony.
Which CRC-32, exactly
The standard one: IEEE 802.3 polynomial, reflected (0xEDB88320), initial value 0xFFFFFFFF, final XOR — bit-for-bit what zlib, zip, gzip and PNG compute. If another tool disagrees with this page, you're almost certainly looking at a different family member: CRC-32C (Castagnoli — iSCSI, ext4), CRC-32/BZIP2, CRC-32/MPEG-2, or POSIX cksum, which is its own thing. Same name, different polynomial, different answer.
Reading the output
Eight hex characters — 32 bits — versus SHA-256's 64 characters. That brevity is the tell when identifying an unknown hash, and also the limitation: with only ~4.3 billion possible values, unrelated files collide by coincidence all the time. Fine for "probably intact," never for "these are the same file." For that, or to check a published checksum of any kind, use the verify tool.
questions
Is CRC32 a cryptographic hash?
No. CRC-32 is an error-detecting code: excellent at catching accidental bit flips and truncation, trivially easy to forge on purpose. Anyone can craft a file with any CRC they like. Use it for corruption checks; use SHA-256 when tampering is a concern.
Which CRC-32 variant does this calculate?
The standard one — the IEEE 802.3 polynomial in its reflected form (0xEDB88320), initial value 0xFFFFFFFF, final XOR — exactly what zip archives, gzip, PNG images and zlib use. If another tool disagrees, it's likely computing a different variant.
Why does my CRC32 differ from another tool's?
Variants. CRC-32C (Castagnoli, used by iSCSI and some filesystems), CRC-32/BZIP2 and CRC-32/MPEG-2 all use different polynomials or conventions, and POSIX cksum is different again. Same name, different math — check which variant the other side expects.
How reliable is CRC32 at catching corruption?
Very good for its purpose: it detects all single- and double-bit errors and all burst errors up to 32 bits. But with only 4.3 billion possible values, unrelated files collide by chance easily — it confirms "probably intact," never "identical" or "authentic".
Why is the output only 8 characters?
CRC-32 produces 32 bits — 8 hex characters — versus 64 for SHA-256. That tiny size is fine for spotting transmission errors and hopeless as an identity. The hash identifier uses that length as its tell.