Privacy
What is File hash?
Also called checksum or hash value.
A file hash is a fixed-length value calculated from a file’s bytes using an algorithm such as SHA-256, used to check that a file hasn’t changed.
How it works
A hash function reads every byte of a file and produces a short fingerprint: 64 hexadecimal characters for SHA-256. The same bytes always produce the same fingerprint, and even a one-byte change produces a completely different one.
That makes hashes useful for checking downloads, confirming a backup copy is identical to the original, or finding byte-for-byte duplicates among photos. The algorithm is part of the comparison: an MD5 value and a SHA-256 value of the same file look nothing alike and can’t be compared with each other.
Hash vs checksum
People use the words interchangeably. Strictly, a checksum is any value used to detect errors, including very simple ones such as CRC32 inside ZIP archives, while a cryptographic hash such as SHA-256 is also designed so nobody can deliberately craft a different file with the same value. When a download page lists a “checksum”, it is almost always a SHA-256 hash.
A practical example
Calculate a downloaded file’s SHA-256 value and compare it with a checksum published through a trusted channel. A mismatch means the bytes don’t match.
What to watch out for
A matching hash doesn’t prove that a file is safe or that its publisher is trustworthy. It only supports an integrity check against the reference you trust.
Tools you can use
- File Hash Checker · Verify a download against its checksum
Go a little deeper
- How to verify a file checksum
- How to open a zip file on a phone or Chromebook
- How to send a folder by email
Common questions
Which hash algorithm should I use?
SHA-256 for anything new. MD5 and SHA-1 are still fine for spotting accidental corruption but are no longer considered safe against deliberate tampering.
Does renaming a file change its hash?
No. The hash is calculated from the file’s contents, not its name or dates, so a renamed copy has the same hash as the original.
Can two different files have the same hash?
In theory, yes, but with SHA-256 the chance of an accidental match is so small that it is treated as impossible in practice.