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Checksum Calculator

Calculate and verify checksums instantly. Generate CRC32, CRC16-CCITT, CRC16-Modbus, Adler-32, XOR, SUM and SHA-256 values from text or raw hexadecimal bytes — right in your browser.

Calculate a checksum

Text is encoded as UTF-8. Hex mode accepts byte pairs such as 48 65 6C 6C 6F or 48656C6C6F.
0 bytes
CRC-16/CCITT-FALSE: polynomial 0x1021, initial value 0xFFFF, no reflection, final XOR 0x0000.

Quick reference

CRC32

A widely used 32-bit cyclic redundancy check for detecting accidental changes in files, archives and data streams.

CRC16

A family of 16-bit CRC algorithms used in embedded systems, serial communications and industrial protocols. Variants have different parameters and results.

Adler-32

A fast 32-bit checksum used in formats and libraries such as zlib. It is not a cryptographic integrity mechanism.

XOR and SUM

Lightweight checksums useful in simple protocols and learning exercises. They can miss many types of data corruption.

SHA-256

A cryptographic hash that produces a 256-bit digest. It is useful for comparing file integrity, but a digest alone does not prove who supplied the data.

Privacy: calculations run locally in your browser. The input is not sent to this page's PHP server by the calculator.

Checksum algorithms explained

A checksum is a value calculated from a sequence of bytes. When the same algorithm is applied to the same bytes, it should produce the same result. Comparing the result with a previously recorded checksum can help identify accidental corruption or changes.

Algorithm Output size Typical use Cryptographic?
XOR-8 8 bits Simple byte-oriented protocols No
SUM-8 8 bits Basic additive error checks No
SUM-16 16 bits Simple checks over byte streams No
Adler-32 32 bits Fast data integrity checks No
CRC-16/CCITT-FALSE 16 bits Serial protocols and embedded systems No
CRC-16/MODBUS 16 bits Modbus RTU communications No
CRC-32/ISO-HDLC 32 bits Files, archives and network data No
SHA-256 256 bits Cryptographic integrity comparisons Yes

Choose the exact algorithm required by your file format or protocol. Two algorithms with the same output length can produce different results because their parameters differ.

How to use this checksum calculator

  1. Select Text (UTF-8) to calculate a checksum from a string, or select Hexadecimal bytes to provide raw byte values.
  2. Enter or paste your data. In hexadecimal mode, enter complete pairs of hexadecimal digits, optionally separated by spaces, commas or colons.
  3. Select the checksum algorithm that matches your application.
  4. Click Calculate checksum to generate the result.
  5. Use Copy checksum to copy the result, or choose Verify a checksum to compare it with a known value.
Important: the input bytes must match exactly. A newline, a space, a different character encoding or a missing byte can change the checksum. In hexadecimal mode, whitespace and separators are ignored.

Frequently asked questions

What is a checksum?

A checksum is a compact value calculated from data. It can help detect transmission errors, accidental modifications or file corruption by comparing the calculated value with an expected value.

What is the difference between CRC16 and CRC32?

CRC16 produces a 16-bit result, while CRC32 produces a 32-bit result. Both use polynomial-based calculations to detect common data errors. The exact polynomial and other parameters determine the specific variant.

Why do two checksum calculators give different results?

They may use different algorithm variants, initialization values, reflection settings, final XOR values, byte ordering or input encodings. Verify that both tools use the same algorithm and exactly the same bytes.

Can a checksum prove that a file is authentic?

No. A checksum or hash can help establish that data matches a known value, but an attacker may replace both the data and an unprotected checksum. For authenticity, use a trusted digital signature or a keyed message authentication code (MAC).

Is SHA-256 better than CRC32?

They serve different purposes. CRC32 is designed for efficient detection of accidental errors. SHA-256 is a cryptographic hash and is more appropriate when comparing data against a trusted digest. Neither one alone authenticates the source of a file.

Does the calculator support binary files?

You can enter binary file bytes as hexadecimal pairs. For example, bytes 48 65 6C 6C 6F represent the UTF-8/ASCII text “Hello”. The calculator processes the supplied bytes rather than opening a file directly.