Standard Paper Sizes used in the UK

A Paper Sizes : A1, A2, A3, A4, A5, A6, A7

A sizes - Standard UK
A0 - 1189mm x 841mm
A1 - 841mm x 594mm
A2 - 594mm x 420mm
A3 - 420mm x 297mm
A4 - 297mm x 210mm
A5 - 210mm x 148mm
A6 - 148mm x 105mm
A7 - 105mm x 74mm

Standard UK Envelope sizes
C6 - 162mm x 114mm
DL - 110mm x 220mm
C5 - 229mm x 162mm
C4 - 324mm x 229mm
C3 - 458mm x 324mm

Standard UK Printing Paper sizes - SRA sizes & B sizes
SRA1 - 900mm x 640mm
SRA2 - 640mm x 450mm
SRA3 - 450mm x 320mm
SRA4 - 320mm x 225mm

B1 - 1000mm x 707mm (Actual paper size in UK is 1020mm x 720mm)
B2 - 707mm x 500mm (Actual paper size in UK is 720mm x 520mm)
B3 - 500mm x 353mm (Actual paper size in UK is 520mm x 360mm)
B4 - 353mm x 250mm

Tolerances specified in ISO 216 for the C series envelope sizes are the same as for A & B series paper sizes and are as follows:
±1.5 mm or dimensions up to 150 mm
±2 mm for lengths in the range 150 to 600 mm
±3 mm for any dimension above 600 mm