Checksum Calculator
Calculate Adler-32, Fletcher, CRC, XOR, and sum checksums.
Adler-32 · 32 bits
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Fletcher-16 · 16 bits
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Internet checksum (RFC 1071) · 16 bits
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CRC-16/ARC (IBM, LHA) · 16 bits
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CRC-32 (ISO-HDLC, zip, PNG) · 32 bits
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CRC-32C (Castagnoli, iSCSI) · 32 bits
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BSD checksum (sum -r) · 16 bits
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System V checksum (sum -s) · 16 bits
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Sum-8 (8-bit sum) · 8 bits
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8-bit two’s complement (Intel HEX) · 8 bits
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XOR-8 (LRC) · 8 bits
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Sum-16 (16-bit byte sum) · 16 bits
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Sum-32 (32-bit byte sum) · 32 bits
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Checksum Calculator
Compute many checksums of text, hex bytes, or a file at once: Adler-32, Fletcher-16, the Internet checksum (RFC 1071), CRC-16 and CRC-32, the BSD and System V sum values, and simple 8/16/32-bit sums, XOR (LRC), and two's-complement checks. Everything is calculated in your browser.
What a checksum is for
A checksum condenses a block of data into a short value so that accidental changes — a flipped bit on a serial line, a truncated download, a corrupted memory card — can be detected by recomputing and comparing. Checksums are fast and small, but they are not secure: an attacker can easily produce data with any desired checksum.
Included algorithms
- Adler-32 – used by zlib; faster than CRC-32 but weaker on short data
- Fletcher-16 – lightweight position-sensitive sum
- Internet checksum – the 16-bit one's-complement sum from IP, TCP, and UDP headers
- CRC-16 / CRC-32 / CRC-32C – strong burst-error detection
- BSD sum / System V sum – the classic Unix
sum -randsum -s - Sum-8/16/32, XOR-8 (LRC), 8-bit two's-complement – common in serial and firmware protocols
Features
- Text, hex, Base64, or file input, up to 200 MB
- Chips to show or hide each checksum
- Hex or decimal output
- Compare with a known value
For dedicated CRC pages see the CRC-16 Hash Generator and CRC-32 Hash Generator. For cryptographic integrity use the SHA256 Hash Generator.
Frequently Asked Questions
What is the difference between a checksum and a hash?
A checksum is a small value used to detect accidental errors, and it is usually fast and short (8–32 bits). A cryptographic hash is much larger and is designed to resist deliberate tampering. Use a checksum for error detection, a hash like SHA-256 for security.
Which checksum should I use?
It depends on the target system. Adler-32 and CRC-32 are common for files and archives, the Internet checksum (RFC 1071) is used by IP/TCP/UDP, and simple XOR or two's-complement sums appear in serial protocols and Intel HEX records. Match whatever the receiving system expects.
What is a longitudinal redundancy check (LRC)?
An LRC is the XOR-8 of all bytes, sometimes followed by a two's-complement. It is used in Modbus ASCII, magnetic stripe cards, and many industrial protocols. Both XOR-8 and the 8-bit two's-complement sum are provided here.
Can I checksum a file?
Yes. Switch to File mode and every checksum is computed from the same file in one local pass. Nothing is uploaded.