What is the default test string 123456789 and why is it used?

The string 123456789 is the universal CRC check vector. Every CRC standard publishes a known result for this exact input. When you run the calculator with this string, you can compare your output to the published check value shown below the result. If they match, the algorithm is set up correctly. It is a quick way to verify that settings like the polynomial, initial value, and reflections are all right.

What is the difference between RefIn and RefOut?

RefIn reverses the bits of each input byte before it enters the CRC register. RefOut reverses all the bits of the final CRC register before the final XOR is applied. Some algorithms use both, some use neither. These settings must match the standard you are following, or your result will be wrong. When you pick a preset algorithm, the calculator sets both values for you.

What is the difference between Normal, Reversed, and Koopman polynomial notation?

Normal is the most common form. It drops the leading 1 bit and shows the rest. For example, CRC-32 uses 0x04C11DB7 . Reversed flips the bit order, which matches how LSB-first shift registers work. The same CRC-32 polynomial becomes 0xEDB88320 . Koopman keeps the leading 1 but drops the trailing 1. All three describe the same polynomial — they just write it differently. The calculator converts between them when you switch the dropdown.

How do I enter hex bytes as input?

Select HEX Bytes as your input format. Then type your bytes separated by spaces, like FF A0 3C . You can also use 0x prefixes, like 0xFF 0xA0 0x3C , or type a continuous hex string with an even number of digits, like FFA03C . The Processed Bytes area below the input will show you exactly how the calculator read your data.

Can I create a custom CRC algorithm?

Yes. Click the Custom button under CRC Width, or choose Custom (manual entry) from the algorithm dropdown. This unlocks all fields so you can type your own bit width, polynomial, initial value, final XOR, and reflection settings. You can set any width from 1 to 64 bits.

What does the Final XOR value do?

After the CRC register finishes processing all input bytes and any output reflection is applied, the final XOR value is XORed with the result. For example, CRC-32 uses a final XOR of 0xFFFFFFFF , which flips every bit of the output. Some algorithms use 0x00000000 , which leaves the result unchanged. This step is the last thing that happens before you get your CRC value.

What does the Run All Algorithms button do?

It computes the CRC of your input using every built-in algorithm at once. The results appear in the table below, where you can sort, filter, and compare them side by side. This is useful when you have a known CRC value and need to figure out which algorithm produced it.

What programming languages does the code generator support?

The calculator generates ready-to-use CRC code in nine languages: C , C++ , Arduino , Python , Rust , Java , JavaScript / TypeScript , C# , and PHP . The code includes the lookup table and a compute function. You can copy it with one click and paste it into your project.

What is the CRC lookup table and why is it useful?

The lookup table has 256 precomputed values. Instead of processing data one bit at a time, software can use the table to process one full byte at a time. This makes CRC calculation much faster. The calculator builds this table for your chosen polynomial and lets you view, copy, or reflect it. The generated source code also uses this table.

Why does my CRC result not match what I expected?

CRC results depend on every parameter being exactly right. Check these things: the polynomial must match your standard, the initial value must be correct, RefIn and RefOut must be set properly, and the final XOR must be accurate. Also make sure your input format is correct. A hex input read as ASCII will give a different result. Use the check value for 123456789 to verify your settings against the published standard.

What is the difference between CRC-16 and CRC-32?

The number refers to the bit width of the output. CRC-16 produces a 16-bit value (up to 4 hex digits), and CRC-32 produces a 32-bit value (up to 8 hex digits). A wider CRC can detect more types of errors and is better for larger blocks of data. CRC-32 is the most common choice for files and network frames. CRC-16 is often used in simpler serial protocols where speed and small size matter more.

Does the calculator work with empty input?

Yes. If you leave the data field empty or clear it, the calculator will compute the CRC of zero bytes. The result depends only on the initial value, the final XOR, and any reflection settings. This can be useful for testing or verifying how an algorithm behaves with no data.

How do I copy the CRC result?

Each result format — hex, decimal, octal, and binary — has a small Copy button next to it. Click that button to copy that specific value to your clipboard. You can also copy the processed bytes, the lookup table, and the generated source code the same way.

What does the step-by-step solution show?

It walks you through the entire CRC calculation from start to finish. It shows the algorithm parameters, the input bytes, the initial register value, the register state after each byte is processed, the output reflection (if used), and the final XOR. This is helpful for learning how CRC works or for debugging when your result does not match.

Is CRC the same as a hash like MD5 or SHA?

No. CRC and cryptographic hashes both turn data into a short value, but they serve different purposes. CRC is designed to catch accidental errors quickly. It is fast but not secure. Hashes like MD5 and SHA are designed to make it very hard to find two inputs with the same output. CRC should never be used for security, passwords, or detecting intentional tampering.

What does the 7-bit data width option do?

Most data uses 8-bit bytes, which is the default. The 7-bit option is for older protocols that send only 7 bits per character, like some forms of ASCII teletype communication. Unless you know your protocol uses 7-bit characters, keep this set to 8-bit.

CRC Calculator - CRC-8/16/32/64, Lookup Table, Code Output

Facebook

X