Type in any box and the others update: decimal, hexadecimal, binary and octal. Or flip individual bits below and watch the value change. Switch on signed mode to see how negative numbers are stored.
In decimal each position is worth ten times the one to its right. In hex it's sixteen, in binary two. Here is your current number broken into positions, with the sum that gets back to it.
One hex digit is exactly four bits and one octal digit exactly three, so they're compact ways to write binary. Two everyday examples, both working.
This is the number from the converter above, at its chosen width. Your browser writes it into memory with a DataView in both byte orders, then runs it through the bitwise operators. JavaScript's operators quietly cut every number to 32 bits; only BigInt keeps all 64.
Converting to any base is repeated division: the remainders, read from bottom to top, are the digits. Pick a base from 2 to 36 to see every step for the converter's number. Then see how JavaScript's built-in parsers read the same text in different ways.
Every limit below was computed with BigInt when the page loaded. The last column shows what the maximum plus one wraps to in two's complement, which is what C, Java, Rust in release builds and most hardware do.
Developer tools people use alongside this one.