How many bits does one octal digit hold?

One octal digit holds three bits, because eight values need three bits.

What is 0o755 in binary?

The octal value 755 is 111101101. Each digit gives three bits.

A byte is two groups of four bits, so two hex digits cover it. Three does not divide eight.

One octal digit holds exactly three bits.

To convert octal to binary, replace each digit with its three bits.

To convert binary to octal, split the bits into groups of three from the right.

The octal value 454 as bits. Edit the expression or select a bit to flip it.

Expression

0b0000000100101100

binary · 16 bits

Replace each octal digit with its three bits: The steps follow the value above.

A permission of 755 becomes 111 101 101, one group for each group of three bits.

A field of three bits in a register reads as one octal digit.

The conversion needs no arithmetic, so it works by eye.

Group the bits from the right. A short group at the left needs zeros in front.
An 8-bit register does not divide into whole octal digits, because 8 is not a multiple of 3.
Hex needs no extra zeros for a byte, which is why a register view uses hex.
Do not mix the prefixes. The value 0o10 is 8 and the value 0b10 is 2.

The full editor holds many values, evaluates expressions across them, and reads live values from a serial port.

How many bits does one octal digit hold?: One octal digit holds three bits, because eight values need three bits.
What is 0o755 in binary?: The octal value 755 is 111101101. Each digit gives three bits.
Why does hex suit a byte better than octal?: A byte is two groups of four bits, so two hex digits cover it. Three does not divide eight.