A standard DL window envelope measures 220x110mm. This is what most people consider a “letter envelope” and fits A4 paper folded into thirds. Business ‘With Compliments’ slips are designed to fit inside a DL envelope. High quality bright white envelopes made from sustainable forest resources. Available in a range of envelope sizes, weights, and pack sizes. DL Window White Envelopes 220x110mm 100 GSM Pack/25pcs.