SHA-512 maps any input to a fixed 512-bit digest: 64 bytes, always 128 hex characters or 88 Base64 characters. This page encodes text as UTF-8 (or reads a dropped file) and hashes it with crypto.subtle.digest. The digest is twice the length of SHA-256's and comes from the same SHA-2 family defined in FIPS 180-4.
The arithmetic behind the numbers: SHA-512 works on 64-bit words over 1,024-bit blocks for 80 rounds, where SHA-256 uses 32-bit words, 512-bit blocks and 64 rounds, which is why SHA-512 is often the faster of the two on 64-bit CPUs despite the longer output. A 512-bit digest puts a generic birthday collision search at 2²⁵⁶ work, against 2¹²⁸ for SHA-256; both are far beyond reach, so the choice is about output length and platform speed, not strength in practice. SHA-384 is SHA-512 with different initial values, truncated to 384 bits (96 hex characters).
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A SHA-512 that does not match a published value: count the characters first. 128 hex characters is SHA-512, 96 is SHA-384, 64 is SHA-256, and the Verify field on this page detects the algorithm from the length and names the one it compared. If the algorithm matches, the bytes differ: a trailing newline, CRLF vs LF, or a UTF-8 BOM in pasted text flips the entire digest, so for files use File mode and hash the file itself.
When a checksum file or protocol specifies SHA-512 (Debian's CD images ship SHA512SUMS files), or when a longer digest is wanted for signatures and key derivation. As a general-purpose default, SHA-256 is shorter and universally supported.
This page is a focused view of theHash Generator: SHA-256, SHA-512, SHA-1, MD5, which has the full set of options.
Both are unbroken members of SHA-2. SHA-512's longer digest gives a larger theoretical margin (2²⁵⁶ versus 2¹²⁸ generic collision work), but neither bound is approachable, so in practice pick by output length and platform: SHA-512 is often faster on 64-bit CPUs, SHA-256 is shorter and has dedicated CPU instructions on more hardware.
512 bits = 64 bytes. As hex that is 128 characters (2 per byte); as Base64 it is 88 characters (4 per 3 bytes, padded).
SHA-384 runs the same SHA-512 computation with different initial values and keeps only the first 384 bits, 96 hex characters. It exists for protocols that want a 384-bit output, such as the TLS cipher suites ending in SHA384; it is not faster.