Calculating your octal permission code is straightforward once you know the Chmod Permissions formula and what each input means. This guide explains the method in plain language, walks through a manual calculation, and gives worked examples you can follow — then you can do it instantly with the Chmod Permissions Calculator.
What is Chmod Permissions?
The Chmod Permissions calculation tells you your octal permission code from a few simple inputs. The figure you are solving for here is the octal permission code.
The Chmod Permissions formula
The core formula is:
Octal permission code = (Owner read (1=yes) × 4 + Owner write (1=yes) × 2 + Owner execute (1=yes)) × 100 + (Group read (1=yes) × 4 + Group write (1=yes) × 2 + Group execute (1=yes)) × 10 + (Others read (1=yes) × 4 + Others write (1=yes) × 2 + Others execute (1=yes))Here is what each input means:
- Owner read (1=yes) — a number. Example: 1.
- Owner write (1=yes) — a number. Example: 1.
- Owner execute (1=yes) — a number. Example: 1.
- Group read (1=yes) — a number. Example: 1.
- Group write (1=yes) — a number. Example: 0.
- Group execute (1=yes) — a number. Example: 1.
- Others read (1=yes) — a number. Example: 1.
- Others write (1=yes) — a number. Example: 0.
- Others execute (1=yes) — a number. Example: 1.
How to calculate it step by step
- Write down the owner read (1=yes) (for example, 1).
- Write down the owner write (1=yes) (for example, 1).
- Write down the owner execute (1=yes) (for example, 1).
- Write down the group read (1=yes) (for example, 1).
- Write down the group write (1=yes) (for example, 0).
- Write down the group execute (1=yes) (for example, 1).
- Write down the others read (1=yes) (for example, 1).
- Write down the others write (1=yes) (for example, 0).
- Write down the others execute (1=yes) (for example, 1).
- Apply the formula above to get your octal permission code.
- Double-check the result with the Chmod Permissions Calculator.
Worked examples
Example 1
| Input / Output | Value |
|---|---|
| Owner read (1=yes) | 1 |
| Owner write (1=yes) | 1 |
| Owner execute (1=yes) | 1 |
| Group read (1=yes) | 1 |
| Group write (1=yes) | 0 |
| Group execute (1=yes) | 1 |
| Others read (1=yes) | 1 |
| Others write (1=yes) | 0 |
| Others execute (1=yes) | 1 |
| Octal permission code | 755 |
With owner read (1=yes) of 1, owner write (1=yes) of 1, owner execute (1=yes) of 1 and group read (1=yes) of 1, the octal permission code works out to 755.
Tips for an accurate result
- Keep your units consistent — mixing, say, months with years or grams with kilograms is the most common source of error.
- Round only at the very end. Rounding inputs early can shift the final answer noticeably.
- Re-run the numbers whenever an input changes, rather than estimating from an old result.
Prefer not to do the maths by hand? — the Chmod Permissions Calculator does it instantly, for free, with the formula and a worked example built in.
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