How (and Why) I Memorized 420 Digits of Pi

There are lots of things I do/have done that I think everyone should do. You should learn about your cognitive biases, learn some basic philosophy/logic, exercise regularly, and generally eat nutritious food. Memorizing 420 digits of pi isn’t one of those things. It’s not for everyone, but I do think more people should do it. So, here’s how and why I did it, so you can judge whether or not you should too.

I’ll start with why. Memorizing 420 digits of pi is a lot easier than most people think, but it will undeniably take some time and effort. So if you’re going to put hours of effort into doing something that is, on the surface, utterly pointless, you definitely need to check under the surface to see if there is any point. I would argue there is. 

Why? 

Short answer: because it’s funny. In addition to 420 being funny, by complete coincidence, it took 69 images. That will make more sense once you’ve read the how, but suffice it to say, this made the whole thing ten times funnier. 

Long answer: 

Using our memory is not something that we need to do very often in today’s society. With Google, Siri, and ChatGPT at our fingertips 24/7, there’s no reason to memorize most things. On its own, I think this is great. It’s great to have access to information without needing to have it memorized. However, such access can become bad when we let it stop us from exercising our memory.

As hunter-gatherers, we never had to think about going for a run or to the gym. Exercise was a part of surviving, so we got it from just going about our daily lives. Now, we can drive to buy some pre-packaged chicken instead of having to chase after it ourselves. This isn’t bad. It allows us to care about other things, but it does mean that we have to put in an extra effort to get our exercise in some other way. Memory is the exact same. Not having to use our bodies in the same way doesn’t mean we no longer need to exercise them to live a healthy life, and memory is no different. 

So you can think about memorizing 420 digits of pi as a back squat for your brain. Just like with back squats, it may start as an exercise to keep you strong and healthy, but it can then turn into something that is intrinsically enjoyable. It allows you to push yourself and discover capabilities beyond what you may have thought possible. It also has some carry-over benefits to other aspects of life. Having a strong memory that you have confidence in will help with far too many things in everyday life to even begin to list here. Plus, if you put the work in to learn how to memorize pi, then you can use the same system to memorize any other numbers: credit cards, phone numbers, or anything else that would be convenient to have easy access to. If you’re convinced, here’s how you can do it.

How?

There are many systems to memorize numbers. I’m only going to talk about the one I used, but if you’re interested, look up others, such as the major system. The system I used is called the Person-Action-Object or PAO system. 

In a nutshell, the way it works is that you assign a person to each two-digit number (i.e. 00, 01, 02…97, 98, 99), then give each person an action and an object. You could do this with only one-digit numbers, but I’m not one for half sends and you shouldn’t be either; plus, you won’t regret going for two-digit numbers, the extra effort on the front end will be well worth it.

Then, to memorize a string of 6 digits, you take the person of the first two, and have them do the action of the second two with the object of the third two. You know that the person always comes first, the action second, and the object third, so you’ll never confuse the order of the 6 digits. 

Example: if I had 972410, I would think of the person I’ve assigned to each of the three sets of two digits. For me, 97 is Connor McDavid, 24 is Kobe Bryant, and 10 is Lionel Messi. Then, to memorize the order, I would have Connor McDavid do Kobe Bryant’s action (dribbling) with Lionel Messi’s object (soccer ball). So if I imagine McDavid dribbling a soccer ball, I know the numbers are 972410.

To memorize 420 digits of pi, I already knew 3.14159, so I didn’t bother coming up with images for that. I started with the next 6. I imagined Crane from Kung Fu Panda firing spiders out of a rocket launcher. Crane is 26, firing a rocket launcher is Rocket Racoon’s (53) action and spiders are Spiderman’s (58) object. So, the next 6 digits in pi are 265358. That’s one image. Each image contains 6 digits, so 69 images get me to 420 (remember, my images start after 3.14159). Easy. 

How do you remember all 69 images?

To remember each image, including the order of the images, I use a memory palace. There are many names for memory palaces and the one I feel is most descriptive is “the journey method.” 

You basically go on a mental journey along a route you already know well. In my case, I start in the rec room of my dorm during my freshman year of college, make my way past the front desk, laundry room, and elevators, then leave the dorm and go to the library. Then, I finish by going inside the library and taking a lap around the second floor. Along the way, I place down my images. 

Example: My first image (Crane, rocket launcher, spiders) is on the piano in the rec room, then my second is on the pool table, third on the ping pong table, and fourth next to the door on the way out. 

Doing it this way, you’ll never confuse the order of your images because you’ll always take the same route to get to your destination. The important trick is that you need to make sure you’re putting your images at obvious and distinct locations along the way. If the locations (or loci if you want to sound like a fancy scientist) are obvious, it will be easier not to skip over them as you go through your journey; if they’re distinct, it will be easier to not confuse one with another. The great thing about this part of the process is that memory palaces can be used to memorize pretty much anything, not just numbers. For example, I have one for remembering every country in the world in order of population.

How do you decide who gets assigned to what number? 

How you assign people to each number is totally up to you. I used a few different methods for assigning people to numbers, so use whichever one or combination of ones that you think would be easiest for you. Just make sure you can visualize the people and the actions clearly and consistently.

Start by making a spreadsheet with 4 columns, the first for every two-digit number, then one each for people, actions, and objects. 

Assigning the people:

• I started by assigning the ones that popped out to me as obvious. Ronaldo 7, Messi 10, Joe Thornton 19, Taylor Swift 22, etc.

• Then, I took sets of ten numbers and gave them a theme. The 70s, for example, are all Harry Potter characters. I associated each number with the respective book: 72, Chamber of Secrets, Dobby; 75, Order of the Phoenix, Umbridge. Then I had Harry, Ron, and Hermione finish it off with 77, 78, and 79, respectively. 

• Then I used initials based on the numbers. For example, no one popped out as obvious for 15, and I didn’t have a theme for the tens, so I took 1 (A) and 5 (E) as the initials and came up with Albert Einstein. Some people use this method for every single number, but I just used it for ones where I couldn’t think of anything better. 

• Finally, I wrapped things up by assigning random people/characters to numbers that completely stumped me, such as a ninja for 17 and an astronaut for 18. 

Assigning the actions and objects:

• For the actions, assign whatever is most obvious, such as Michael Jordan dunking, but if you can’t, then just put whatever as long as it’s distinct from all your other actions (you don’t want one person doing pull-ups and another doing chin-ups, those would be way too easy to confuse). Then, do the same with the objects. 

Once you’re done, translating from numbers to PAO and back will feel a bit like learning a new language. You’ll have to consult your sheet every now and then, and you’ll be quite slow to start. But, just like with language, you’ll get faster with practice, and unlike with language, you only have 300 things to memorize, most of which will be extremely obvious. I’m not going to lie, this part will take some time, but I think it’s completely worth it because you’ll then have an easy, effective, and efficient way to memorize numbers for the rest of your life. It comes in handy more often than you may think.

Extra Tips

Here are a few more tips to make things even easier. 

• Give motion to your images: If your images involve lots of movement, they will be much easier to remember.

• Bring in as many senses as possible: If you can incorporate smell, touch, hearing, or taste in addition to just sight when you’re making your images, they will stick much better.

• Add emotion: If there’s an image you find particularly disgusting, exciting, amusing, or anything else, really let yourself feel that emotion when you visit that image. 

• Use active recall: When you review your images, which you must do, actively recall them. Don’t look at your sheet or the digits of pi, try to pull your images and their associated number out purely from memory, then confirm that you’re right. If you need to consult your sheet, make yourself struggle to pull it out of memory before you give up and look at it.

• Use spaced repetition: Gradually review less and less frequently. After you place down an image, review it a few minutes later, then again in 10 minutes, then half an hour, then a few hours, then a few days, then weeks, etc. The best time to review something is right before you forget it (and make sure you review it using active recall!)

• Have fun: Corny, I know, but this is the most important part. If you enjoy this process, which you should be able to do because many of these images will be very entertaining, then it will be far easier.

Happy memorizing!

If you’re interested in this kind of memory stuff, Joshua Foer’s book Moonwalking with Einstein and Nelson Dellis’s YouTube channel are fantastic places to get into it more.