Decimal to octal

Decimal value

Octal 755

Divide by eight, keep the remainders

The same number elsewhere

Decimal 493

Binary 111101101

Binary, grouped 0001 1110 1101

Hexadecimal 1ED

Bits needed 9

Note

Group binary into threes

The same number in each base

Decimal	Binary	Octal	Hex
0	0	0	0
1	1	1	1
8	1000	10	8
10	1010	12	A
15	1111	17	F
16	10000	20	10
64	1000000	100	40
100	1100100	144	64
255	11111111	377	FF
256	100000000	400	100
1024	10000000000	2000	400
65535	1111111111111111	177777	FFFF

Divide repeatedly by eight and read the remainders backwards. 493 gives 755. Alternatively convert to binary and group the bits into threes from the right — each group is one octal digit.

How to convert decimal to octal

1 Enter the decimal number.

2 Read the octal result.

3 Check the binary form to see the three-bit grouping.

4 Prefix with 0o if pasting into modern code.

Going via binary is usually faster than dividing by eight. Convert to binary, group the bits into threes from the right, and read each group — the grouping is exact because 8 is 2 cubed. This is the same trick that makes hex easy, with three bits instead of four, and it works for any base that is a power of two.

Questions

What is 493 in octal? −

755, which as Unix permissions is rwxr-xr-x.

How do I convert quickly? +

What prefix marks octal? +

What is 8 in octal? +

Is octal still used? +

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