Double SHA256
Calculate Double SHA-256—SHA-256 applied twice—from UTF-8 text, hexadecimal bytes, Base64, or other encodings. Read more
What is Double SHA256?
Double SHA-256, often written SHA256d, calculates SHA256(SHA256(message)): the second pass hashes the 32 raw bytes produced by the first pass, not its 64-character hexadecimal display. It is used in Bitcoin data structures such as block-header hashes, as documented in the Bitcoin block chain reference, but it is not a general replacement for single SHA-256.
How to use this hash calculator
Enter the source and choose the encoding that represents the intended bytes. For serialized protocol data shown as hexadecimal, select Hex input; UTF-8 input would hash the visible hex characters instead. Select the desired display encoding for the final 32-byte result.
Result example
Double SHA-256 of UTF-8 abc is 4f8b42c22dd3729b519ba6f68d2da7cc5b2d606d05daed5ad5128cc03e6c6358 in Hex.
Important limitations
Double SHA-256 is unkeyed and does not encrypt or authenticate data. It should not be used directly for password storage. Protocols may also display hash bytes in reverse order, so a visually reversed Bitcoin identifier can still represent the same underlying bytes.
Frequently asked questions
Why does my result differ from another tool?
Check whether the source is text or decoded hexadecimal bytes, whether the reference expects single or double SHA-256, and whether its displayed byte order is reversed.
Can I use the result to verify data?
Yes, when the protocol explicitly specifies Double SHA-256 and the expected value comes from a trusted source. For ordinary SHA-256 or HMAC-SHA-256, use the SHA-256 calculator.