3-7/8  x 8-7/8  Self-Sealing Security Business Envelope with Double Window #9 - White (24 lb.) (500 per box) Ideal for mailing invoices, letters, and other documents requiring two windows. Self-sealing security envelopes feature blue tint for privacy and confidentiality. Top window size is 1-3/16  x 3-1/2 . Bottom window size is 1  x 4 . 