I think you may have seen a another thread with one of my posts about using a Prexie stamp as a gauge for other stamp issues, so let me elaborate a few points to clarify and illustrate.
1. A perforation gauge is one of the most basic tools for any collector. It will make your journey through the hobby much more rewarding if you obtain a good one and learn how to use it correctly. Otherwise ...
2. The "Fourth Bureau" issue is the definitive series in use from 1923-1938. I did not know the term "Fourth Bureau" as a beginner, so I thought should make that clear here from the start since it is not necessarily obvious. This issue comes with several perforation rates, printing methods (flat & rotary), and in sheet/booklet/coil formats. Thus a perforation gauge is one valuable tool for differentiating them. Fortunately, there are no watermarks to contend with in this series. Here are two stamps which match your two:
(The point being that your 3 cent stamp is not a "Prexie" issue.)
3. The "Prexies" are the definitive series in use beginning in 1938, featuring (mostly) the US Presidents. The sheet versions of all values up to the 50 cent are all perf 11x10.5, here are the lowest values:
4. The point of another thread to which I think you are referring was in the absence of a perforation gauge, a stamp of known
gauge can be used in place of a perforation gauge. In this case, aligning the long side of the 2 cent Prexie (known to be 10.5) against the unknown 4th Bureau issue shows a match with both the 1 cent and the 3 cent stamps. Thus they can only be #632 and #635, just like yours. The top perforations of all 3 stamps in this post will be perf 11.
If the long sides did not align with the Prexie stamp as perf 10.5, then the Fourth Bureau stamp must be something else. I could use the top of the Prexie (known to be perf 11) against the long side of the Fourth Bureau to test for that match, etc.
5. "11.25", the listed perforation rates in the catalogs are rounded off slightly to the nearest half, thus 11x11. Don't get too caught up in the measurement being off by a tenth. You will not truly get exactly 10 or 10.5 or 11.
Still, get a perforation gauge and become adept at using it.
I hope this made it clearer.