In 1977, I bought 5,000 military surplus patches for a song. They were supposed to be for the M-14 and were roughly 2.5 inche squares of cotton fabric packed in little kraft paper envelopes about 20 or 25 each. It is turning into a lifetime supply. I use them as-is on my 45 ACP pistol. I cut them in half lengthwise for use on 9mm and 38 Special. And I cut them into quarters for use with 22 caliber.
Any size that will fit tightly enough in the barrel that you have to use some effort to push it through will do a sufficient job cleaning the bore and depositing oil back on it.