CRC-16 Calculator
Free, client-side, works offline.
Loading tool...
What is CRC-16 Calculator?
CRC-16 Calculator computes 16-bit cyclic redundancy check checksums — the error-detection workhorse of embedded and industrial protocols. Ten standard variants (Modbus RTU, CCITT-FALSE, XMODEM, Kermit, X-25, IBM/ARC, USB, MAXIM/iButton, GENIBUS, DNP3) are computed simultaneously with their exact parameters, so firmware engineers can match datasheets and protocol analyzers without guessing.
Key Benefits
- Ten variants computed at once
- Exact catalog check values
- Text and hex input modes
- File upload up to 10MB
- Full parameter transparency
- Works offline in the browser
Common Use Cases
- •Verifying Modbus RTU frame checksums
- •Debugging SCADA/DNP3 traffic
- •Implementing bootloader CRC checks (XMODEM)
- •Checking Dallas 1-Wire device data
- •Cross-checking protocol analyzer captures
How to Compute a CRC-16 Checksum
- Choose input mode: Pick Text for UTF-8 strings or Hex bytes for raw protocol payloads like 01 04 02 FF FF.
- Enter data: Type or paste your data, or upload a file (up to 10MB) which is converted to hex bytes.
- Select variant: Choose the variant your protocol uses, e.g. CRC-16/MODBUS for Modbus RTU. The parameter table shows poly, init, refin, refout and xorout.
- Copy the result: Copy the checksum in hex, or hit Compare all variants to see every result side by side and identify which CRC a device is using.
Key Features
- 10 CRC-16 variants: Modbus, CCITT-FALSE, XMODEM, Kermit, X-25, IBM, USB, MAXIM, GENIBUS, DNP3
- Correct catalog check values (verified against CRC-16/arc catalog)
- Text and hex-byte input modes
- File upload up to 10MB with hex conversion
- Parameter table with poly/init/refin/refout/xorout
- Hex, decimal, and binary outputs with one-click copy
Frequently Asked Questions
What is the difference between CRC-16/Modbus and CRC-16/IBM?
Both use the same polynomial (0x8005) and reflected processing, but Modbus starts from init 0xFFFF while IBM/ARC starts from 0x0000, producing different checksums for the same data.
Why do CCITT-FALSE and XMODEM give different results?
They share the polynomial 0x1021 and non-reflected processing, but CCITT-FALSE initializes the register to 0xFFFF while XMODEM uses 0x0000.
Is CRC-16 secure against tampering?
No. CRC-16 detects accidental errors (noise, corruption) and was never designed as a security hash. For authenticity use HMAC-SHA256 or similar cryptographic MACs.
How do I compute a Modbus RTU CRC by hand?
Take the raw message bytes, run CRC-16/MODBUS (poly 0x8005, init 0xFFFF, reflected), then append the low byte first and the high byte second (little-endian) to the frame.
Does text input include the UTF-8 BOM?
No. Only the characters you type are encoded as UTF-8. If you need a BOM (EF BB BF) in the checksum, switch to hex mode and prepend it manually.