Accepted formats: spaces, commas, new lines, optional 0x prefix, or continuous hex string.
Optional. Useful for protocol-specific initial checksum values.
What is a hexadecimal checksum?
A hexadecimal checksum is a compact value calculated from a set of bytes. It is used to detect accidental data corruption during storage or transmission. You will see checksums in serial protocols, firmware updates, packet headers, embedded systems, and binary file formats.
Hexadecimal representation is simply a human-friendly way to view bytes. Since each byte maps cleanly to two hex digits (00 to FF), checksum work is usually written and shared in hex.
How to use this calculator
- Paste your hex bytes in the input box.
- Select a checksum method, or choose Show all common checksums.
- Optionally enter a seed value when your protocol starts from a non-zero checksum.
- Click Calculate checksum.
The tool normalizes your input bytes and returns the checksum in both hexadecimal and decimal formats.
Supported checksum modes
8-bit additive sum
Adds all bytes and keeps only the lowest 8 bits. This is common in lightweight packet formats where speed and simplicity are more important than strong error detection.
16-bit additive sum
Same concept as the 8-bit version, but keeps 16 bits. This reduces collisions compared with 8-bit sums.
8-bit XOR checksum
XORs every byte together. It can catch many single-bit and odd patterns quickly, and is frequently used in microcontroller serial messages.
One's and two's complement checksums
These are derived from the additive sum:
- One's complement: invert all bits.
- Two's complement: invert bits, then add 1.
Two's complement is often used when the checksum byte should make the total byte sum equal zero (mod 256).
Internet checksum (16-bit one's complement)
This is the classic checksum used in IP/UDP/TCP headers. Bytes are processed as 16-bit words using one's-complement arithmetic with end-around carry.
Worked example
Suppose your payload is: 01 A0 FF 2B.
- 8-bit sum:
0xCB - 8-bit XOR:
0x75 - 8-bit two's complement (of sum):
0x35
In a simple framed protocol, appending 0x35 may cause the full frame sum to wrap to zero,
which is a common validation strategy.
Common input mistakes
- Using non-hex characters (anything outside 0-9 and A-F).
- Supplying an odd number of hex digits in a continuous string.
- Confusing ASCII text with hex bytes (for example,
41is hex for ASCII "A").
If the calculator reports an error, check your separators, prefixes, and digit counts first.
Final note
Checksums are excellent for detecting random transmission errors, but they are not cryptographic integrity tools. If your use case requires tamper resistance or authentication, use a cryptographic hash or MAC in addition to a checksum.