A1 Envelope Postage
An A1 envelope, also sold as 4 Bar, measures 3 5/8 x 5 1/8 in. At 1 oz or less it is a standard letter and needs $0.82, one Forever stamp.
Your answer
Standard letter
No extra postageRegular letter postage. No surcharge.
- Postage per piece
- $0.82
- 100 invitations
- $82.00
Stamps for each one
1 × Forever (1 oz letter)
Why
- This is a standard letter: within 6.125 x 11.5 in, no thicker than 0.25 in, and length divided by height is 1.41 (it must be between 1.3 and 2.5). USPS rule
Rates last verified on
100 invitations: $82.00 in postage ($0.82 each, standard letter)
The smallest envelope you can safely mail
USPS will not accept a letter under 3 1/2 in high or 5 in long. The A1 clears both by exactly 1/8 in. That is why it became the default reply envelope: it is about as small as mail gets.
The thin margin matters if you buy from a maker whose "4 Bar" runs small, or if you are tempted by a mini envelope a size down. Anything under the minimum is not charged extra. It is simply not mailable.
What the A1 is used for
Most A1 envelopes carry an RSVP card of 3 1/2 x 4 7/8 in back to the hosts. One card in one envelope is far below 1 oz, so a single Forever stamp covers it with room to spare.
If you pre-stamp the reply envelopes, that is $0.82 per guest household on top of the outer envelope. For 100 invitations it adds $82.00. The RSVP postage guide covers the choices, including the cheaper reply postcard.
Address direction is not optional here
On a larger envelope, writing the address along the short side only costs you the surcharge. On an A1 it makes the piece unmailable, because USPS measures length along the address and 3 5/8 in is under the 5 in minimum.
If you print reply envelopes yourself, keep the address running along the 5 1/8 in side.
A common reply card is too small for a postcard
It is tempting to skip the envelope and mail the reply card as a $0.65 postcard. The usual A1 reply card, 3 1/2 x 4 7/8 in, cannot do that: postcards must be at least 5 in long, and it is 1/8 in short. If you want postcard replies, order cards cut to 3 1/2 x 5 in or 4 1/4 x 5 1/2 in instead.
Compare the options
| Option | Mail class | Each | For 100 |
|---|---|---|---|
| A1, address along the long side | Standard letter | $0.82 | $82.00 |
| A1 with a wax seal | Nonmachinable letter | $1.31 | $131.00 |
| A1, address along the short side | Not mailable as is | Not mailable | - |
| Bare 3.5 x 5 reply postcard instead | Postcard | $0.65 | $65.00 |
Questions and answers
How many stamps does an A1 envelope need?
One Forever stamp ($0.82) covers an A1 envelope up to 1 oz with nothing lumpy or rigid inside.
Is an A1 envelope big enough to mail?
Yes. At 3 5/8 x 5 1/8 in it is 1/8 in over the USPS minimum of 3 1/2 x 5 in in both directions.
Is A1 the same as 4 Bar?
Yes. A1 and 4 Bar are two trade names for the same 3 5/8 x 5 1/8 in envelope.
Can I use a postcard stamp on an A1 reply envelope?
No. The $0.65 postcard price is only for a bare card with no envelope. An A1 envelope needs letter postage of $0.82.