Johnny Decimal-ising my life

Colin Wren
6 min readApr 17, 2021


Photo by Daniel on Unsplash

A couple of months ago I was browsing HackerNews and came across a post about the Johnny Decimal system — A means of organising projects in a manner to how the Dewey Decimal system organises libraries.

This appealed to me as I have way too many projects on the go, split across multiple devices (six at last count), multiple cloud offerings (Dropbox, Google, iCloud) and multiple external drives, so being able to consolidate these and retain easy access was a strong selling point (as it’s often hard to find files when you don’t know what combination of machine and drive they’re on).

Of course life got in the way and so ‘Johnny Decimalise files’ was de-prioritised again and again, but I finally had some time off work and was able to sit down and go through the process.

Having completed that task I feel like I’ve regained some sort of control over my life and I’ve been able to see the breadth of experience I’ve had over the last 8ish years that I’ve been collecting these different files.

I also found a bitcoin wallet backup from 2013 which may or may not have 0.1BTC in it which I’ve forgotten the password to, so that’s going to be something I’ll be looking at getting access to shortly (0.1BTC was about £30 back then, it’s now about £4,000)

How Johnny Decimal works

The Johnny Decimal website goes into the full details behind the process but I’ll cover the basics so you’ve got an idea of what’s involved.

To put it simply though, you create 10 categories, each with 10 areas and then in those areas you can create an infinite number of items.

The areas have a number (dictated by the category they are in) and the items have a second number so the Johnny Decimal number for an item becomes [area].[item].

Johhny Decimal works well because of the numbering system and the shallow folder structure, it becomes easy to sort and find files but also the decimal value means you can use this elsewhere and build up a bigger system for classifying everything in your life.

I think the system works well because it’s flexible enough to grow it as you go through the process of sorting your files. I had multiple instances of finding really old files that would have up-ended a more strict process but was able to easily create new categories and items to cater for these.

1. Define your areas

The first step is to create up to 10 overarching areas that will represent what your file system contains. Each category has a number range associated with it which indicates the numbers being used by its subfolders.

I only ended up having 5 areas:

  • 10–19 Finances — For tax stuff mostly
  • 20–29 House — For lease agreements and paperwork from when I almost bought a flat last year
  • 30–39 Hobbies — For files I’ve generated as part of the different hobbies I have
  • 40–49 Professional — For work stuff but also projects I’ve had in the past
  • 50–59 Personal — For things like my 5 year plan and correspondence with people

2. Define your categories in those areas

The second step is slightly harder as you’re still bound by having up to 10 categories per area so you’ve got to start grouping things if you find yourself hitting that limit.

That being said I only struggled with this in the Professional area due to the ridiculous amount of projects I’ve done in the past, eventually I just put them under a ‘projects’ category.

The category has a number based on the area it lives within.

For example my Hobbies area has these categories:

  • 30 Gaming — For screenshots of games, save files etc
  • 31 Music — For guitar tabs, Logic projects, LSDJ saves etc
  • 32 Art — For drawings, photos of screen prints etc
  • 33 Photography — For photos, each item will be an album of photos
  • 34 Reading — For eBooks, I could also tag books I own with their item number
  • 35 Computing — For backup files from apps mostly
  • 36 Travel — For travel plans, emails for trips etc

3. Add items in your categories

The third step is pretty easy, at this point you’ve got a hierarchy of where everything should go, the next step is to ensure that you can create an item in your category that doesn’t have any sub-folders.

This may mean extracting subfolders into their own items or just deciding that an item is a category in it’s own right. Johnny Decimal doesn’t set hard rules on what sits at what level so it’s flexible enough to allow this.

Each item will have a decimal number associated with it. This is a combination of the category number and the item number and is the key to making it easy to find files as you can memorise the number easily or note it down and then traverse the file structure to find it.

To re-use my Hobbies example my Travel category has the following items:

  • 36.01 Chicago 2019
  • 36.02 Dortmund 2019
  • 36.03 Japan 2022
  • 36.04 Japan 2017

Note how the folders aren’t necessarily in chronological order — This was because I found the files relating to Japan 2017 after I found the others.

Technically I could correct this but there’s no connotation that a Johnny Decimal number represents when the event happened or when the files were created — It’s about having a system to find things easily.

Sorting your files using Johnny Decimal

The Johnny Decimal system makes it ridiculously easy to sort files as until the item level there’s only folders in each directory — here’s the process I followed when cleaning up my email inbox (which had about 500 unsorted emails).

  • Drop files into the area they should be in
  • Go through each area and drop the files in that area into the category they should be in
  • Go through each category in each area and drop the files into an existing item or create a new one

As I was doing this across multiple devices and multiple storage solutions I created a page in my Notion that listed out the hierarchy of each area, category and item so I could make sure I had consistent numbering.

The process of sorting my emails took about 20 minutes and that was mostly due to the speed of a new page of emails loading so working on a collections of local files would likely be even quicker.

A question of storage

After going through all my devices and storage solutions I had to decide how I was going to merge the different collections of files. I knew I wanted to use one of the cloud storage accounts I have but I wasn’t sure which one.

In the end as I’m tied into the iOS ecosystem I decided to use iCloud as I pay for extra storage and there was a means to use it in a similar manner to Dropbox on Windows.

This then allowed me to delete my Dropbox account and has put me one step closer to removing my need to have a gmail account.

One consideration I had to have was where to store source code for my programming projects. I decided that I would put these on GitHub and store these outside of the Johnny Decimal structure. This way I could keep the cloud storage usage lean and it gave me a good excuse to populate my GitHub.


Taking the time to go through the Johnny Decimal process allowed me to get my digital (and physical) life in order, cut down the services I use and gave me an excuse to go over my old projects.

It’s also given me a system to map every aspect of my life and being able to see a full hierarchy of everything I’ve done so far was really cool.

I was also able to find that Bitcoin wallet which, while I don’t have the password, means I might even have some long-forgotten riches waiting for me.



Colin Wren

Currently building Interested in building shared understanding, Automated Testing, Dev practises, Metal, Chiptune. All views my own.