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Modulo 256 Checksum (Sum8)

Calculate Sum8 (Modulo 256) checksums from ASCII text or hexadecimal byte sequences

Enter data above to calculate the checksum.

What Is Sum8 (Modulo 256 Checksum)?

Sum8 — Modulo 256 Checksum

Sum8 is a simple error-detection method used in protocols and file formats. All byte values are summed together and the result is taken modulo 256, yielding a single 8-bit checksum byte.

How the Sum Works

Each byte value (0–255) is added to a running total. After all bytes are processed, the final total is reduced modulo 256 (i.e., only the lowest 8 bits are kept). A mismatch on the receiver side indicates data corruption.

Hex Input Format

Enter bytes in any format: continuous (F6A30D), space-separated (F6 A3 0D), comma-separated (F6, A3, 0D), 0x-prefixed (0xF6 0xA3 0x0D), or concatenated 0x (0xF60xA30x0D). All formats and mixed separators are accepted.

How to Use Sum8 Checksum

  1. 1Choose Text for plain ASCII strings or Hex for raw byte sequences.
  2. 2In Text mode every character is converted to its ASCII byte value.
  3. 3In Hex mode enter bytes in any format: space-separated (F6 A3 0D), comma-separated (A1, B2, C3), 0x-prefixed (0xA1 0xB2), concatenated 0x (0xA10xB20xC3), or continuous (F6A30D).
  4. 4The Sum8 checksum is the arithmetic sum of all input bytes modulo 256. Results are shown in HEX, DEC, OCT and BIN.

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