Introduction
A checksum is a short code made from data. If even one bit of the data changes, the code changes too. That makes checksums a fast way to check if a file or message is still correct.
This free online checksum calculator makes that code for you. Type text, paste hex bytes, upload a file, or load a URL. Then pick an algorithm and get the result right away. Everything runs in your browser, so your data stays on your computer.
You can choose from many hash and checksum types:
- Cryptographic hashes: MD5, SHA-1, SHA-224, SHA-256, SHA-384, SHA-512, SHA3, and RIPEMD-160
- Simple checksums: Adler-32, Fletcher-16, and Fletcher-32
- CRC codes: CRC-8, CRC-16, CRC-32, CRC-32C, and more
The tool also does more than just print a hash. You can turn on HMAC to add a secret key, paste a known checksum to verify a download, and view the result in hex, Base64, decimal, or binary. A step-by-step section shows how the answer was found, and a chart shows each byte of the digest. If you only need a plain digest with no CRC options, the Hash Value Calculator is a simpler starting point, while the CRC Calculator focuses on cyclic redundancy checks alone.
How to use our Checksum Calculator
Pick an algorithm, enter your text, file, or hex data, and the calculator shows the checksum or hash value in hex, Base64, and more, plus the steps used to get it.
Hash Algorithms tab: Click this tab to use a hash function like MD5, SHA-1, SHA-256, SHA-512, SHA-3, RIPEMD-160, Adler-32, or Fletcher.
Hash / checksum algorithm: Choose the hash you need from the drop-down list. SHA-256 is the default and is a safe pick for most files.
CRC Algorithms tab: Click this tab to use a CRC check instead, such as CRC-8, CRC-16, or CRC-32.
CRC variant: Pick the exact CRC type, like CRC-32, CRC-32C, or CRC-16-CCITT. Each one uses its own polynomial and start value.
Polynomial representation: Leave this on the preset choice to match the standard CRC value. Change it to Normal, Reversed, or Reversed reciprocal only if you need a different bit order.
Quick pick buttons: Tap any button in the list to jump straight to that algorithm.
Input format: Choose Text if you are typing words, or Hex String if you are pasting hex bytes like 54 68 65. To convert those bytes to other bases first, try the Hex Calculator or the Binary Calculator.
Data to hash: Type or paste the data here. The box below shows how many bytes and characters you entered.
Upload a file: Pick a file from your device to hash it. Files up to 32 MB work, and they stay in your browser.
Load from URL: Paste a web address and click Load URL to fetch a file and hash it. Some sites block this, so upload the file if it fails. For big files, the Download Time Calculator can estimate how long the transfer will take.
Auto-Calculate: Leave this on to get results as you type. Turn it off if you want to press Calculate yourself.
Enable HMAC: Turn this on to make a keyed hash, then type your secret key in the box. Use the eye button to show or hide the key.
Calculate and Reset: Press Calculate to run the hash, or Reset to go back to the sample values.
Lowercase / Uppercase: Switch the letter case of the hex result to match the format you need.
Expected checksum: Paste the known checksum from the file's source, then click Verify. The tool says MATCH or NO MATCH, and ignores case, spaces, colons, and a leading 0x.
Copy and Download: Use Copy Output to copy the result, or Download Result to save it as a text file.
What Is a Checksum?
A checksum is a short code made from a file or a piece of text. You run the data through a math formula, and it gives back a fixed-length string of numbers and letters. If even one bit of the data changes, the checksum changes too. That makes it an easy way to check if a file arrived whole and unchanged.
Why People Use Checksums
- Check downloads. Many websites post a SHA-256 value next to a file. You hash the file you downloaded and compare the two codes. A match means the file is good.
- Find errors. Networks, hard drives, and ZIP files use CRC codes to spot bits that flipped by accident. Storage admins often pair this with a RAID Calculator when planning redundancy.
- Compare files. Two files with the same hash are almost always the same file.
- Store passwords safely. Apps save a hash instead of the real password.
Hash Functions vs. CRC
Cryptographic hashes like SHA-256, SHA-512, SHA-3, and RIPEMD-160 are built to be hard to fake. It should be impossible, in practice, to make two different files share one hash. Use these when security matters.
CRC codes like CRC-32 and CRC-16 are fast but not secure. They catch random mistakes, not attacks. Anyone can change a file and fix the CRC to match. Use CRC for error checking only.
Simple checksums like Adler-32 and Fletcher-16/32 sit in the middle. They are very fast and used inside formats like zlib, but they are also easy to fool.
Common Algorithms and Digest Sizes
| Algorithm | Output size | Good for |
|---|---|---|
| MD5 | 128 bits (32 hex chars) | Old file checks only — broken for security |
| SHA-1 | 160 bits (40 hex chars) | Legacy systems — no longer safe |
| SHA-256 | 256 bits (64 hex chars) | The common choice today |
| SHA-512 / SHA-3 | 384–512 bits | Extra strength, long-term use |
| CRC-32 | 32 bits (8 hex chars) | ZIP files, Ethernet, quick error checks |
A Warning About MD5 and SHA-1
Both MD5 and SHA-1 are broken. Researchers can build two different files that share one hash. They still work fine for spotting accidental damage, but never trust them for signatures, passwords, or proof that a file is safe. Pick SHA-256 or better.
CRC Polynomial Forms
Every CRC is based on a polynomial written as a hex number. The same polynomial can be written three ways: normal (as written, bits shift left), reversed (bits flipped, used by CRC-32 and CRC-16-IBM), and reversed reciprocal (Koopman form). The math result depends on which form and bit order you use, so a CRC-32 in normal form will not match the value your ZIP program shows. Each CRC variant has one standard form, and that is the one you almost always want. The bitwise XOR steps behind each shift are easier to follow with an XOR Calculator, and the remainder idea comes from plain modulo arithmetic.
What HMAC Adds
HMAC mixes a secret key into the hash. Without the key, no one can create a matching code, even if they have the message. APIs and web tokens use HMAC to prove a message came from the right sender and was not edited on the way. Plain hashes cannot do this, because anyone can hash anything.
Hex, Base64, and Case
A hash is really just a string of bytes. Hexadecimal is the usual way to show it, with two characters per byte. Base64 packs the same bytes into fewer characters, which some tools prefer. Upper and lower case hex mean the exact same value, so A3FF and a3ff match. If you need to move between number bases while checking a digest, the Binary to Decimal Calculator handles the conversion.
Tips for Comparing Checksums
- Make sure both codes come from the same algorithm. A SHA-256 will never match a SHA-1.
- Check the length. 32 hex characters is MD5, 40 is SHA-1, 64 is SHA-256.
- Spaces, colons, and a leading
0xdo not change the value. - Text hashes depend on encoding and on hidden characters. An extra newline at the end changes the whole result.
Related Technology Tools
- Hash Value Calculator — quick MD5, SHA-1, and SHA-256 digests for text and files.
- CRC Calculator — CRC-8, CRC-16, and CRC-32 remainders with polynomial details.
- Subnet Calculator — split networks and read host ranges.
- CIDR Calculator — turn prefix lengths into address blocks.
- IP Address Calculator — inspect any IPv4 address in binary and decimal.
- Data Transfer Calculator — work out how much data a transfer moves.
- Bandwidth Calculator — size a link for your traffic load.
- Chmod Calculator — build Unix permission bits in octal and symbolic form.