About the Chmod Calculator
On Linux, macOS and other Unix systems every file and folder has permissions for three groups of people: the owner, the group and everyone else. Each group can be allowed to read, write and execute. The chmod command sets them, usually with a three-digit number. This calculator lets you tick the boxes and see the number, the symbolic form such as rwxr-xr-x, a plain-English summary and the finished command, or type a number and see the boxes. Type the permissions you want, or an octal number such as 755 and the chmod permission number appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Chmod Calculator
- 1Enter the permissions you want, or an octal number such as 755.
- 2Pick the units or options from the menus if the chmod permission number tool offers them.
- 3Read the chmod permission number in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the chmod permission number
Web developers and system administrators set permissions every day: 755 for programs and folders that everyone may enter, 644 for ordinary files that only the owner may change, 600 for private keys and 700 for private folders. Getting the number right avoids both security holes and mysterious permission errors.
The calculator works in both directions. If a tutorial tells you to run chmod 640 and you want to know what it does, type the number and read the summary. If you know what access you want, tick the boxes and copy the command.
How the chmod permission number is worked out
Read = 4, write = 2, execute = 1. Add the values you want for each of the three groups to get one digit, then write the three digits in the order owner, group, others. Permissions rwxr-xr-x are 4+2+1 = 7 for the owner, 4+1 = 5 for the group and 4+1 = 5 for others: chmod 755. Permissions rw-r--r-- are 6, 4, 4: chmod 644. Permissions rwxr-x--- are 7, 5, 0: chmod 750.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Tick boxes or type the number
- Symbolic form such as rwxr-xr-x
- Ready-made chmod command
Mistakes to avoid with chmod permission number
A very common mistake is to use 777 to get rid of an error. That lets anybody write to the file, which is a security risk, especially on a web server. Another is forgetting that folders need the execute bit to be entered. Special bits such as setuid are not covered by this tool.
On phone and computer
On a phone, type into the boxes one after another and read the chmod permission number underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the chmod permission number move. The chmod calculator works the same on both. Permissions are built from octal digits, so Number Base Converter, Octal to Decimal Converter and Decimal to Octal Converter help you check each digit. Cron Expression Generator is the next stop when a script needs to run on a schedule.
Features
- Avoid 777
- Folders need execute
- Keep private keys at 600
- Clear messages when the chmod permission number inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate chmod permission number?
Read = 4, write = 2, execute = 1. Add the values you want for each of the three groups to get one digit, then write the three digits in the order owner, group, others. Permissions rwxr-xr-x are 4+2+1 = 7 for the owner, 4+1 = 5 for the group and 4+1 = 5 for others: chmod 755. Permissions rw-r--r-- are 6, 4, 4: chmod 644. Permissions rwxr-x--- are 7, 5, 0: chmod 750.
What is the formula for chmod permission number?
Read = 4, write = 2, execute = 1. Add the values you want for each of the three groups to get one digit, then write the three digits in the order owner, group, others. The chmod calculator applies it exactly and rounds only the displayed answer to six significant figures.
What does chmod 755 mean?
The owner can read, write and execute; the group and others can read and execute. It is the usual setting for programs and public folders.
What does chmod 644 mean?
The owner can read and write; everyone else can only read. It is the normal setting for web pages and documents.
What does the execute bit do on a folder?
It allows people to enter the folder and reach the files inside. Without it, even a readable folder cannot be used.
Is this chmod calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.