Paper Size Metric mm Imperial Inches
A0 841 x 1189 33.1 x 46.8
A1 594 x 841 23.4 x 33.1
A2 420 x 594 16.5 x 23.4
A3 297 x 420 11.7 x 16.6
A4 210 x 297 8.3 x 11.7
A5 148 x 210 5.9 x 8.3
15" x 20" 381 x 508  
20" x 30" 508 x 762  
30" x 40" 762 x 1016  
40" x 60" 1016 x 1524  
Measurement Conversion:
Millimeters to Inches DIVIDE by 25.4 e.g. 1000mm to inches is 1000 / 25.4 = 39.37 inches
Inches to Millimetres MULTIPLY by 25.4 e.g. 12 inches to mm is 12 x 25.4 = 304.8mm