편지봉투 envelope 규격...펌

On the internet I find these PRC sizes:
PRC Envelope #1 102 x 165 mm
PRC Envelope #2 102 x 176 mm
PRC Envelope #3 125 x 176 mm
PRC Envelope #4 110 x 208 mm
PRC Envelope #5 110 x 220 mm
PRC Envelope #6 120 x 230 mm
PRC Envelope #7 160 x 230 mm
PRC Envelope #8 120 x 309 mm
PRC Envelope #9 229 x 324 mm
PRC Envelope #10 324 x 458 mm

Also see these US sizes (a.o.):
US Envelope #9 3 7/8 x 8 7/8
US Envelope #10 4 1/8 x 9 1/2
US Envelope #11 4 1/2 x 10 3/8
US Envelope #12 4 \276 x 11
US Envelope #14 5 x 11 1/2

My wild guess is that US means United States. If that is true, PRC may mean Peoples Republic of China.

Here in Europe we use size names that are not related to a country. They are defined in the International standard ISO 269 and have names like:
Envelope B4 250 x 353 mm
Envelope B5 176 x 250 mm
Envelope B6 176 x 125 mm
Envelope C3 324 x 458 mm
Envelope C4 229 x 324 mm
Envelope C5 162 x 229 mm
Envelope C6 114 x 162 mm
Envelope C65 114 x 229 mm
Envelope DL 110 x 220 mm