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Unix Permission Calculator (chmod)

Convert between octal, symbolic and rwx Unix file permissions, with special bits and a chmod command.

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Unix Permission Calculator (chmod) is free to use as often as you like, directly from this page. You will find it under Data & computing, with ASCII Table Reference and Citation Generator (APA / MLA / Chicago) for the neighbouring cases.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What does Unix Permission Calculator (chmod) do?

Convert between octal, symbolic and rwx Unix file permissions, with special bits and a chmod command.

When would I actually use this?

Finding out how big a thing will be before you make it: how many gigabytes an hour of footage takes, how long a file needs on the connection you have, how large a photo prints before it goes soft, what bitrate fits the budget you were given.

What is the most common mistake?

Taking the advertised connection speed as the transfer speed. A 100 Mb/s line is megabits, the file is in megabytes, and the eight-fold difference between them is where most download estimates go wrong — before overhead and contention take their own share.

How is Unix Permission Calculator (chmod) different from ASCII Table Reference?

They sit next to each other but answer different questions: ASCII Table Reference is the one to open when you need it to full ASCII table (0-127) with a decimal / hex / octal / binary / character converter and a text-to-codes panel. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Citation Generator (APA / MLA / Chicago) is the closest one after this: Generate a correctly formatted reference-list entry and in-text citation (or footnote) in APA 7, MLA 9 or Chicago 17 for websites, books, journal articles and newspapers, with one-click copy.

What else is worth having open alongside it?

Depth of Field (DoF) Calculator and Exposure Triangle Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

Byte prefixes follow the IEC convention where a kibibyte is 1 024 bytes and a kilobyte is 1 000 — drive makers use the second, operating systems often report the first, and a disk that shrinks on arrival is that gap and nothing else. Print sizing assumes 300 dpi unless you change it.

Further reading

All guides →
ExplainerHow Unix File Permissions Work: Reading 755 Without GuessingRead is 4, write is 2, execute is 1, and each of the three digits describes a different party. The part most explanations get wrong is what the execute bit does on a directory — it grants traversal, not the right to run anything.How-toHow to Write a Cron Expression: Five Fields and the OR Rule Nobody MentionsMinute, hour, day of month, month, day of week. The traps are that a step is a stride through a range and not an interval, and that the two day fields are combined with OR — so 0 0 1 * 1 fires on the 1st and on every Monday.ExplainerThe Golden Hour and the Blue Hour Are Angles, Not HoursGolden hour runs from +6° to −4° of solar elevation and blue hour from −4° to −6°, which is why it lasts forty minutes at the equator, over an hour at mid-latitudes, and above 72.6° in June does not happen at all. The thresholds this calculator uses, checked against its own output.ExplainerDepth of Field: What Actually Controls ItFour variables set depth of field, and subject distance dominates the other three. The exact formulas, a computed table, why the circle of confusion is a decision rather than a measurement, and what "full frame has less depth of field" really means.ExplainerThe Exposure Triangle Is Three Routes to the Same StopA stop is a factor of two in light. The f-number scale is powers of √2 for a reason you can derive in one line, EV = log2(N²/t) puts a number on it, and the three controls are equivalent in brightness only — never in the picture.ExplainerCrop Factor: What It Changes and What It Does NotCrop factor is a ratio of sensor diagonals. It changes framing, not the lens — proved by computing field of view both ways — and it applies to the f-number as well as the focal length, which is the half most articles leave out.