#10 White Left Window Envelopes - Size 4 1/8 X 9 1/2 - 24lb. - 100 Envelopes - Superfine Inc. Brand #10 White Window envelopes made from premium 24 lb. white wove stock; 4.12 x 9.5 inch; 100 envelopes per box. window size is 1.12 x 4.5 inch, positioned 7/8" from left, 1/2" from bottom. Envelope is ideal for all business, professional and personal correspondence; Poly-Klear left window position eliminates need to address envelope. moisture activated gummed seal.