[en-vuh-lohp, ahn-]

An envelope is a packaging product, usually made of flat, planar material such as paper or cardboard, and designed to contain a flat object, which in a postal-service context is usually a letter, card or bills. The traditional type is made from a sheet of paper cut to one of three shapes: the rhombus (also referred to as a lozenge or diamond), the short-arm cross, and the kite. These designs ensure that in the course of envelope manufacture when the sides of the sheet are folded about a delineated central rectangular area, a rectangular-faced, usually oblong, enclosure is formed with an arrangement of four flaps on the reverse side, which, by virtue of the shapes of sheet traditionally used, is inevitably symmetrical.

In 1876 Ben published the Stationer's Handbook. He worked for the Samuel Raynor & Company in New York. He created the first commercial sizes of envelopes and simply numbered them from 0 through 12. It was mostly for social and business stationery purposes in those days. That's how the No. 10 envelope got its name.



Window envelopes have a hole cut in the front side that allows the paper within to be seen. They are generally arranged so that the sending address printed on the letter is visible, saving the sender from having to duplicate the address on the envelope itself. The window is normally covered with a transparent or translucent film to protect the letter inside, as was first designed by Americus F. Callahan in 1901 and patented the following year. In some cases, shortages of materials or the need to economize resulted in envelopes that had no film covering the window. One innovative process, invented in Europe about 1905, involved using hot oil to saturate the area of the envelope where the address would appear. The treated area became sufficiently translucent for the address to be readable. A typical use for window envelopes is courtesy reply mail.


The "envelope" used to launch the Penny Post component of the British postal reforms of 1840 was a lozenge-shaped lettersheet known as a Mulready. If desired, a separate letter could be enclosed with postage remaining at one penny provided the combined weight did not exceed half an ounce (about 13 grams). This was a legacy of the previous system of calculating postage, which partly depended on the number of sheets of paper used.

During the U.S. Civil War those in the CSA occasionally used envelopes made from wallpaper, due to financial hardship.



As envelopes are made of paper, they are intrinsically amenable to embellishment with additional graphics and text over and above the necessary postal markings. This is a feature that the direct mail industry has long taken advantage of -- and more recently the Mail Art movement. Custom printed envelopes has also become an increasingly popular marketing method for small business.

Most of the over 400 billion envelopes of all sizes made worldwide are machine-made. Some will be made by hand. These include some of the eastern poorer countries.

Post office requirements

According to international postal conventions, a letter envelope must measure at least 90 × 140 mm. The length of postcards and aerograms must be at least the width times the square root of 2. These requirements help sorting letters by making it easier to line up all the envelopes with the addresses reading the same way.

The same regulations also reserve certain regions on the envelope for the address, the postage, as well as markings that can be added by sorting machines.

In some countries using postcodes, common envelopes are preprinted with lines and boxes that help write those postcodes in a consistent way in a consistent position.

In Australia, post office-preferred envelopes have four boxes printed in orange ink at the bottom right-hand corner where handwritten postcodes are meant to be written. Character recognition software is used to read the postcode number.

Envelopes in the Soviet Union were printed with something like the common 7 segment LCD, to assist the user to write the 6-character postcode directly in machine-readable format.

While conforming to postal regulations can save postage and lead to a faster and more reliable delivery, postal workers usually try to deliver also more non-standard forms of envelope.

International standard sizes


Format Dimensions (mm) Suitable for content format
DL 110 × 220 1/3 A4
C7/C6 81 x 162 1/3 A5
C6 114 × 162 A6 (or A4 folded in half twice)
C6/C5 114 × 229 1/3 A4
C5 162 × 229 A5 (or A4 folded in half once)
C4 229 × 324 A4
C3 324 × 458 A3
B6 125 × 176 C6
B5 176 × 250 C5
B4 250 × 353 C4
E3 280 × 400 B4


North American sizes

There are dozens of sizes of envelopes available. Not all are used for posting mail, but for such things as former pay packets or putting a gift card or a key in. U.S. and Canadian postal regulations differ from those of the rest of the world; although envelopes are still deliverable worldwide by the regulations of the Universal Postal Union, the sorting machines will not accept the international sizes. This is not as much a difference as usually thought, for the location of sending address and return address differ between Germany and France, for example.

Most envelope sizes in this system have names, not designations. The designations under the system "A2", etc., do not correspond to ISO paper sizes.

Format Dimensions (in) Dimensions (mm) Ratio
A2 4 3/8 × 5 3/4 110.3 × 144.9 131%
A6 4 3/4 × 6 1/2 119.7 × 163.8 137%
A7 5 1/4 × 7 1/4 132.3 × 182.7 138%
No. 6¾ 3 5/8 × 6 1/2 92.1 × 165.1 179%
No. 9 3 7/8 × 8 7/8 98.5 × 225.5 229%
No. 10 4 1/8 × 9 1/2 104.0 × 239.4 230%

See also


External links

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