Help 10 Cents Stamp From 1923 Monroe

Good morning,
I'm new to the world of stamps and I have questions about some of them, which I'll share with you later.
I'd like your help with the perforation of this stamp. Do you think it's 9 1/2 or 10? And if it's 9 1/2, could you give me some information because I can't find anything.
Thank you very much.

measure the top and side perfs as well

In short, your stamp is Scott 591, perf 10x10.

As for a longer answer, the choices you have are perf 11, perf 10, and perf 11x10.5
Scott and other catalogs could be more clear about this, but catalogs "round" perforation rates to the nearest 0.5 (or some to the nearest 0.1 or 0.25 depending on the issue and era). You have found such an example, where all of the "perf 10" U.S. stamps of the early 20th century gauge slightly less than 10. Nor will you find exact 11's. Find the best match and go forward. Your encounter also depends somewhat on whether your gauge is accurate (there are some which aren't). In many cases, it is equally easy to use a stamp of known rate as a gauge and eliminate the rounding effect.

Thank you very much