• # Question: How many digits in the pi number have you been able to memorise?

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Asked by on 15 Jun 2020. This question was also asked by .
• Helen Fletcher answered on 15 Jun 2020: last edited 15 Jun 2020 7:17 pm

I somehow just know the first 10 digits now – I think I might have been born with them programmed in :’) Learning more is something I’ve always meant to do, but not quite gotten around to yet.

I do know the first n digits of some other iconic numbers, like the Golden Ratio and the square root of 2 (but pi is my favourite).

• Sophie Carr answered on 16 Jun 2020:

Personally, 3.142 as that’s all I’ve ever needed for my maths! Some people have memorised lots more digits.

• Chris Budd answered on 16 Jun 2020:

When I work with pi I use

3.1415926535897932…

Yes .. I really DO need to know all of these digits. Modern GPS systems which I work
with have to work to insane levels of accuracy to function, and part of this means that
they have to use very accurate values of pi. It is quicker to memorise these than to
look them up every time.

But .. you can also calculate pi using the utterly wonderful formula

pi/4 = 1 – 1/3 + 1/5 – 1/7 + 1/9 – 1/11 + 1/13 – 1/15 + ….

• Chelsea Houghton answered on 16 Jun 2020:

Only 8, although anything past 2-4 decimal places isn’t really used

• Katy Tant answered on 16 Jun 2020:

I know the first 8 – I’ve never tried to learn any more!

• Liam Brown answered on 16 Jun 2020:

Eight. I don’t really need that many — usually 3.141 is enough — but over time you just end up picking it up.

• Alexandre Borovik answered on 16 Jun 2020:

I remember pi as 3.1415926 — mostly because of the poetic rhythm of digit when they are pronounced in Russian, my native tongue. I hardly ever use pi; if I do, pi = 3 suffices. I was lucky that at school, I was taught the art of quick back of an envelope, or even mental, estimates for rough approximate answers to physics problems, at university I was taught to do rough estimates for problems in economics; not much practical use, but it helps when I read newspapers. I explained that because I remember one curious thing about pi: it is pretty close to the square root of acceleration of gravity on the surface of Earth. And this is explained by history: meter as a standard unit of length was proposed in the 18th century and defined as the length L of a pendulum with the half period T = pi * sqrt[L/g] of small oscillations T = 1 second (at the latitude of Paris). After some discussion it was replaced by 1/20,000 part of the length of the meridian through Paris, which was easier to measure with high precision, but happened to be approximately the same. If we substitute T= 1 and L= 1, we see that 1 = \pi*sqrt[1/g], and, measured in second and meters, pi = sqrt[g].

• Maja Popovic answered on 16 Jun 2020:

I just remember 3.141

And for “e”, 2.7172

Never really needed the rest.

• Richard Pinch answered on 16 Jun 2020:

There are many tricks for remembering pi: one is to find a memorable sentence in which the number of letters in each word gives you a digit of pi. My favourite is

How I wish I could recollect pi easily.

• Omduth Coceal answered on 16 Jun 2020:

Irrational as it might seem, I once learnt the first 100 digits of pi. It was a good challenge. Then I thought “what’s the use of that”? I’ve only ever needed to use 3.142 in calculations. If more accuracy is required you probably need to use a computer code anyway. And to be honest, in many calculations I’ve been all too happy to leave the answer in terms of pi. Rarely have I needed to compute actual numbers!…

• Hannah Speed answered on 16 Jun 2020:

I learned the first 6, but my brother used to know it to 20!

• Andrew Harrison answered on 16 Jun 2020:

I know pi as far as 3.1415926 but I always rely on the constant in whatever programming language I’m using. Most programming languages can only be guaranteed to be accurate to 6 or 8 places. So there’s no need to know it more accurately than that.

• Arick Shao answered on 18 Jun 2020:

I remember 3.14159 off the top of my head, but I’d start stumbling after that!

These days, there are very few situations where one would need to memorise digits of pi. (We make computers do the really nasty computations!) Also, there are probably not very many people that you can impress by reciting digits of pi.

A more interesting question is to ask (1) how you could compute pi up to, say, 500 decimal places, and (2) how you would know that the number you found is actually accurate to 500 decimal places.