Question: what is the difference between b4 and c4 envelopes?
Answer: For example, B4 is between A3 and A4 in size, and B5 is between A4 and A5. The C series was introduced to provide an envelope with enough space for an A series sheet. ... That is, a sheet of A4 easily fits into a C4 envelope. The C sizes are just between the A and B series.