64-bit Hex Endian Converter
Swap the byte order of a 64-bit (8-byte) hex value — locked to exactly 8 bytes, padding or rejecting input that doesn't fit.
Built by
Swapnil SanghviFull-Stack Web Developer & WordPress Developer
Swapnil Sanghvi is a full-stack web and WordPress developer, UI designer, and full-time freelancer who builds and maintains Hex Calculator.
Further reading: Endianness — Wikipedia
How 64-bit Byte Swap Works
Pad the value to exactly 16 hex digits (8 bytes) if it's shorter, then reverse the order of those 8 bytes. A value that needs more than 8 bytes is rejected rather than truncated.
Where 64-bit Byte Swap Actually Comes Up
Converting a 64-bit File Offset or Size Field
Large files and modern file formats often use 64-bit offsets — converting between a file format's declared byte order and your code's native order is a standard parsing step for these fields.
64-bit file offset in a container format
Reading a 64-bit Timestamp or Large ID
Some systems represent high-precision timestamps or large unique IDs as 64-bit integers — endian conversion may be needed when such a value crosses between systems with different native byte order.
64-bit snowflake-style ID
Verifying a uint64_t Swap Function
Checking that a language's or library's 64-bit byte-swap function (like C's __builtin_bswap64) produces the expected result for a known test value.
confirm bswap64 output against this calculator
Why Use This Calculator Instead of Doing It by Hand
- Locks to exactly 64 bits, catching a value that doesn't fit rather than silently mishandling it
- Pads shorter values to the full 8 bytes automatically
- Runs entirely in your browser — nothing you type gets sent anywhere
- Removes the ambiguity of a general-purpose converter when you specifically need 64-bit width
Limitations
- Locked to exactly 64 bits (8 bytes) — a value with more digits returns an error instead of being truncated or reinterpreted.
- This is a pure byte-order swap, not a bit-order reversal — the bits inside each byte stay in the same order.
Frequently Asked Questions
Why use a fixed 64-bit converter instead of the general one?
It guarantees the result is always exactly 8 bytes, which matters when working with a value you know is a specific 64-bit type (like a uint64_t, a 64-bit timestamp, or a file offset) and want consistent, explicit padding.
What happens if my value needs more than 8 bytes?
It's rejected with an error rather than silently truncated — this converter is locked to exactly 64 bits, so a larger value means either the wrong tool or a data-size mismatch worth investigating.
What's a common 64-bit value that needs endian conversion?
64-bit file offsets, large IDs, and some timestamp formats are stored as 64-bit integers — converting their byte order comes up when moving such values between systems or file formats with different native endianness.
Does this pad a shorter value automatically?
Yes — a value with fewer than 16 hex digits (8 bytes) is padded with leading zeros to fill the full 64 bits before the byte order is reversed.