I rarely use pi. But when I do I only use 3 digits. I wish I could use less, but we still need to use change when we make purchases.

Mechatronics student. If your not using 3.1416 at a minimum, then your doing it wrong.

Back in middle school I memorized this much of pi (for no good reason):

3.14159265358979323846264338327950288419716939937510

That’s far more accurate than I’ll ever need.

The digital field, and we use the first ten digits, especially when those first ten digits is some person's password with the password hint "easy as pi".

Chip R&D. We only use 1's, 0's if management is feeling generous. There are no circles, no need for pi.

This probably won’t play well with this audience, but I’m a management/strategy consultant. “~5” (technically one decimal place but also rounded to the nearest interval of 5) for any C-level decks ;)

In Biostatistics - only ever use pi in the variance of the logistic density. Using 3.14 gives substantially equivalent results to using arbitrarily large precision. But I use whatever my calculator or R give me.

Equipment engineering. Usually 2 if I'm doing math by hand. 5 for more accurate calculations.

I don't use Pi but I do use GPS fairly often and try to get down to 7 digits after the decimal point. Our equipment probably isn't quite that accurate though lol so the seventh digit is likely a guess. Probably even the 6th digit.

Molecular biology. 4 digits.

Mechanical engineer here - Matlab uses 16 digits for pi(), so that's my go-to. When doing some larger thermodynamic simulations, I sacrifice some digits of pi to get more computational headroom. But that's only after I get really annoyed at the code, and it almost never helps (but rarely hurts, as well)

I can't say "professionally" but I learned CAD design with FreeCAD, and know the topological naming issue thoroughly.

Almost all "mystery" problems in CAD are due to a combination of the hacks that get around the Topological Naming Issue and π.

In CAD, you cookie, you brownie, you might even salad, but you stay the hell away from importing π as a reference on anything complex. For 3D printing, I never need better than 0.05mm so 3.1416.

Embedded engineer, working in education. I use 3 for mental estimations and whatever is stored in the calculator, I have happened to grab, for "precision" work. Sometimes I'll even round pi to 4, to build in some tolerance when calculating materials.

I work in the Bakery field and our specialty is Pie.

One digit

I'm a nothing in particular, and I used to remember 100 digits. I could probably remember again in an hour.