In USA, Canada and parts of Mexico you can find the following paper sizes. The 4 most commonly used US standard paper sizes are known as Letter, Legal, Ledger and Tabloid.
Canadian paper sizes
In Canada they also use P series.
P1
560 x 860 mm
22.0 x 33.9 in
P2
430 x 560 mm – 16.9 x 22.0 in
P3
280 x 430 mm – 11.0 x 16.9 in
P4
215 x 280 mm – 8.5 x 11.0 in
P5
140 x 210 mm – 5.5 x 8.3 in
P6
105 x 140 mm – 4.1 x 5.5 in
International standard for papers
Most countries don’t use US standard paper sizes. The A-series is the International Standard for paper sizes (ISO).