Envelope Size & Mailing Guide
#10 envelope: 9.5 x 4.125 in (standard business)
USPS Letter: max 11.5 x 6.125 in, 0.25 in thick, 3.5 oz
USPS Large Envelope/Flat: max 15 x 12 in, 0.75 in thick, 13 oz
Envelope weight estimate: ~5-10g for standard, ~15-25g for catalog