Envelopes: Business, Mailers and Pouches

Size codes and windows: how the paper sits inside

The number on an envelope is a size standard. A number 10 envelope, 4 1/8 by 9 1/2 inches, holds a letter folded in thirds, and a number 9 is slightly smaller so it fits inside as a reply envelope. Announcement sizes like A-7 suit cards and invitations, and square or clasp envelopes carry flat documents. Windowed envelopes show the address printed on the letter, so choose single or double window to match your template and fold, and test one sheet before ordering a box.

Paper weight, security tint and closure

Paper weight is quoted in pounds, with 24 lb the common office standard and 28 lb noticeably heavier and more opaque. Security tints, such as a blue woodgrain pattern printed inside, hide the contents of statements and records. Closures vary: gummed flaps need moisture, self-seal strips press shut, and clasp and open-end styles suit bulky papers. Kraft stock is stronger and suits heavier loads; poly and corrugated mailers add protection for flat items. Box quantities often run into hundreds, so confirm the count.

Questions about Envelopes: Business, Mailers and Pouches

What size envelope fits a letter?

A letter-size sheet folded in thirds fits a number 10 envelope, and a folded A4 sheet fits as well. Windowed versions need the address to sit exactly where the window is, so do a test fold first.

What is a security tint envelope?

It has a printed pattern inside, often a blue woodgrain or similar, that stops the contents showing through when held to the light. It is used for confidential mail such as statements and records.

What does 24 lb mean on an envelope listing?

It is the weight of the paper stock, based on a standard ream. 24 lb is typical office weight, while 28 lb is thicker and more opaque. Higher weights feel more substantial and hide the contents better.