Paper sizes - Overview formats
 
The German DIN paper sizes originate already from the early 30's.
DIN A0 is a paper format of 1qmtr surface with an aspect ratio of 1:1,414.
The format DIN A1 develops thereafter with the halving of DIN A0.
DIN B/C sizes are oversizes, which are meant for envelopes.
DIN B is in the surface exactly 1,414 as largely as DIN A.
DIN C lies exactly between the two sizes.
A A4 format fits in a C4 cover and a C4 format into a B4 envelope.

In the USA there are other formats.
ISO (International Organization for Standardization) / DIN (German Industrial Norm) / JIS (Japan Industrial Standard)
 

   
ISO / JIS / DIN A ISO mm ISO inch US name US inches   Fix sizes
4A0 1682x2378 66.22x93.62        
2A0 1189x1682 46.81x66.22        
A0 841x1189 33.11x46.81 E 34x44   Poster / Technical Drawings
      F 28x40    
A1 594x841 23.39x33.11 D 22x34   Poster / Technical Drawings
A2 420x594 16.54x23.39 C 17x22   Drawings / Diagrams / Large Tables
      Super A3/B 13x19    
A3 297x420 11.69x16.54 B ledger 11x17   Newspapers / Drawings / Diagrams / Large Tables
      Legal 8.5x14    
A4 210x297 8.27x11.69 A letter 8 1/2x11   Letters / Magazines / Forms / Catalogs
      Executive 7.5x10    
A5 148x210 5.83x8.27 5x8 5x8   Note pads / Books
A6 105x148 4.13x5.83 Microfiche 4.13x5.83   Postcards / Books
A7 74x105 2.91x4.13 3x5 3x5    
A8 52x74 2.07x2.91 Businesscard 2x3 1/2   Playing Cards
A9 37x52 1.46x2.05        
A10 26x37 1.02.x1.46        
             
ISO / DIN B ISO mm ISO inch       Variable sizes
B0 1000x1414 39.37x55.67        
B1 707x1000 27.83x39.37        
B2 500x707 19.69x27.83        
B3 353x500 13.90x19.69        
B4 250x353 9.84x13.90        
B5 176x250 6.93x9.84       Books
B6 125x176 4.92x6.93       Books
B7 88x125 3.46x4.92        
B8 62x88 2.44x3.46       Playing Cards
B9 44x62 1.73x2.44        
B10 31x44 1.22x1.73        
             
JIS B ISO mm ISO inch       Variable sizes
B0 1000x1414 39.37x55.67        
B1 707x1000 27.83x39.37        
B2 500x707 19.69x27.83        
B3 353x500 13.90x19.69        
B4 250x353 9.84x13.90       Newspapers
B5 176x250 6.93x9.84        
B6 125x176 4.92x6.93        
B7 88x125 3.46x4.92        
B8 62x88 2.44x3.46        
B9 44x62 1.73x2.44        
B10 31x44 1.22x1.73        
             
ISO / DIN C ISO mm ISO inch       Variable sizes
C0 917x1297 36.10x51.06        
C1 648x917 25.51x36.10        
C2 458x648 18.03x25.51        
C3 324x458 12.76x18.03        
C4 229x324 9.02x12.76       Envelopes for A4 letters: unfolded
C5 162x229 6.38x9.02       Envelopes for A4 letters: folded once
C6 114x162 4.49x6.38       Envelopes for A4 letters: folded twice
C7/6 81x162 3.19x6.38        
C7 81x114 3.19x4.49        
C8 57x81 2.24x3.19        
C9 40x57 1.57x2.24        
C10 28x40 1.10x1.57        
             
ISO / DIN D ISO mm ISO inch       Variable sizes
DL 220x110 8.66x4.33