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CRC32 and Checksum Calculator: CRC16, CRC32, Adler-32

This free checksum calculator computes CRC32, two CRC16 variants and Adler-32 for text or hex bytes. It is useful for checking data, comparing files and testing protocols.

By Debmedia Technologies LLP · Kolkata, India · Updated

What Is It and When Do You Need It?

A checksum is a small fingerprint of some data. Archives, network packets, file formats and firmware use CRCs to notice corruption. Developers often need to compute one to match a specification.

Paste text or hex bytes and read four common checksums.

How to Use This Tool

  1. Paste text or hex bytes.
  2. Choose how to read the input.
  3. Press Calculate.
  4. Copy the checksum you need.

How the Calculation Works

CRC32 uses the reflected polynomial 0xEDB88320 with start value 0xFFFFFFFF and a final XOR. CRC16-CCITT-FALSE uses polynomial 0x1021 with start 0xFFFF. CRC16-XMODEM uses the same polynomial with start 0. Adler-32 keeps two running sums modulo 65521.

Worked Example

The text 123456789 gives CRC32 CBF43926, CRC16-CCITT 29B1, CRC16-XMODEM 31C3 and Adler-32 091E01DE.

Common Uses

  • Checking a download or file.
  • Matching a protocol specification.
  • Testing code against known values.
  • Teaching error detection.

Tips and Common Mistakes

  • Check which variant a specification uses.
  • Spaces and line endings change the result.
  • Use SHA-256 for security.
  • A Windows file with CRLF line endings has a different checksum from the same file with LF endings, which is a common reason two checksums do not match.

Next, you may need the bitwise calculator, IEEE 754 converter, Base58 encoder, ASCII table.

Everything runs in your browser. Nothing you type is uploaded, stored or sent to any outside service.

Frequently Asked Questions

A cyclic redundancy check is a short number computed from data. If the data changes, the CRC almost always changes too, so it detects accidental errors.
No. It is for detecting accidents, not attacks. For security use a hash such as SHA-256.
The text 123456789 has CRC32 CBF43926, CRC16-CCITT-FALSE 29B1, CRC16-XMODEM 31C3 and Adler-32 091E01DE.
The standard one used in ZIP, PNG and Ethernet (polynomial 0xEDB88320, reflected).

Disclaimer: results are calculated in your browser from the numbers you enter. Check important results before you rely on them for money, health, safety or legal decisions.