USPS: Letters & Flats
Send domestic First Class letters and flats with Postsale's USPS integration
In This Article
Quickly purchase and print postage for your domestic First Class letters and flats with Postsale’s built-in USPS integration. Depending on what fits your workflow best, you can choose to print on standard 4" x 6" or compact 2" x 1.5" labels.
In this article, we will look at:
- The differences between letters and flats
- Printing to 4" x 6" vs. 2" x 1.5" label stock
- Weight and dimension requirements for letters and for flats
- How to configure a shipment to print postage for letters and flats
- Non-machinable options
Before We Begin
This article assumes that you have added your USPS account to Postsale and that you have orders imported into Postsale that you wish to ship as a First Class Letter or Flat.
Postage for Letters & Flats
Letters vs. Flats: What's the Difference?
USPS classifies a mailpiece as either a letter or flat based on its size, shape, and flexibility. A letter is typically a standard envelope. It's rectangular, flat, and small enough to fit in a mailbox. Letters must be at least 3.5 inches high by 5 inches long and no more than 6.125 inches high by 11.5 inches long, with a maximum thickness of 0.25 inch.
A flat, on the other hand, is larger and more flexible. Think of items like large envelopes, newsletters, or magazines. Flats can be up to 12 inches high, 15 inches long, and 0.75 inch thick. To qualify as a flat, the item must be flexible and uniformly thick. Rigid or uneven items might be charged at parcel rates instead.
If your mailpiece is too large to be a letter but doesn’t exceed the flat-size limits, it’s considered a flat.
Quick Comparison
| Mail Type | Minimum Size | Maximum Size | Max. Thickness | Max. Weight |
|---|---|---|---|---|
| Letter | 3.5" x 5" | 6.125" x 11.5" | 0.25" | 3.5 oz |
| Flat | Over max. letter size | 12" x 15" | 0.75" | 13 oz |
General Examples
Common Letters
- Standard envelopes, such as a #10 envelope
- Birthday/Greeting cards
- Checks sent in envelopes
Common Flats
- Large manila envelopes
- Magazines or catalogs less than .75" thick
- Padded mailers less than .75" thick
Printing Letter and Flat Labels
You have the option of printing letter and flat labels to 4" x 6" or 2" x 1.5" label stock. We recommend double-checking that Postsale is set up correctly for the label size you will be printing your letter and flat postage to. Here's how:
Procedure: Settings > Account Settings
- Go to Settings.
- Select Account Settings.
- Select Printing.
Select the Correct Label Template
4" x 6" Labels
You may have previously configured Postsale's printer settings to print to your 4" x 6" labels when you first configured Postsale. If so, great! If either of the following templates are selected in the Printing screen, you're all set.
- Label 4 x 6 (wide)
- Label 4 x 6 (tall)
When you print your letter or flat labels, they print with the From address, To address, and the correct postage formatted for your 4" x 6" label stock. Here's an example:
2" x 1.5" Labels
When printing your letter and flat postage to a roll of 2" x 1.5" labels, you'll want to make sure to select the Label 2 x 1.5 (wide) template prior to purchasing your postage so that Postsale knows to format the labels correctly for your printer and label stock.
With this template selected, your letter and flats postage will print to your 2" x 1.5" labels like this:
Remember to Set the Template Back to 4x6
If you typically print postage for your packages, like USPS Priority Mail, FedEx Ground, UPS Ground, etc., to 4" x 6" label stock, be sure to set the Printer label template back to the correct 4 x 6 template once you're finished printing letter and flat postage.
Configure Your Shipments for Letters or Flats
In this section, we will look at how to configure a single shipment as a letter or flat. Check out our Ship Your Orders help article for more information on how to configure your shipments and how to print postage for multiple orders.
- Select the order you wish to ship.
- Open the Dock.
- Verify that the shipment is selected in the Shipments Grid.
- Expand the Package section if it isn't already expanded. Then…
- Select either Letter or Flat from the Packaging drop-down menu.
- Enter the correct Weight, Length, Height, and Thickness for the letter or flat. (See the Quick Comparison chart in the Letters vs. Flats: What's the Difference section above for weight and dimension requirements.)
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- Expand Additional Details. Then, verify that USPS is selected as the Carrier and that USPS First Class Mail is selected as the Service.
The correct rate is shown in the Dock's Rate Selector for the correctly configured shipment.
Aspect Ratio Surcharge
Letter-sized mailpieces are considered non-machinable and can incur a surcharge when the mailpiece has an aspect ratio (the length divided by the height) of less than 1.3 or more than 2.5.
For example, a letter with the dimensions of 10 inches by 3.5 inches has an aspect ratio of 2.875 and is considered non-machinable by USPS.
10 / 3.5 = 2.875
Since Postsale displays the rates generated by USPS, the rate will be displayed in the Rate Selector so that you are aware of any additional surcharges.
Non-Machinable Options
USPS uses automated machines to sort most mail, but some items can’t go through those machines due to their shape, rigidity, or contents. These are considered non-machinable, and a non-machinable surcharge may be applied.
Flats
Most flats are already sorted manually due to their size, so USPS doesn’t apply a "non-machinable" surcharge to flats in the same way they do for letters. However:
- Flats must still be flexible and uniformly thick
- If a flat is too rigid, bulky, or uneven, it may be reclassified and charged at parcel rates
Letters
A letter is considered non-machinable if it meets any of these conditions:
- Polybagged: The letter is polybagged, polywrapped, enclosed in any plastic material, or has an exterior surface made of a material that is not paper. Windows in envelopes made of paper do not make mailpieces nonmachinable. Attachments allowable under applicable eligibility standards do not make mailpieces nonmachinable.
- Closure Devices: The letter has clasps, strings, buttons, or similar closure devices.
- Loose Items: The letter contains items such as pens, pencils, keys, or coins that cause the thickness of the mailpiece to be uneven; or loose keys or coins or similar objects not affixed to the contents within the mailpiece. Loose items may cause a letter to be nonmailable when mailed in paper envelopes.
- Rigid: The letter is too rigid (does not bend easily when subjected to a transport belt tension of 40 pounds around an 11-inch diameter turn).
- Self Mailer: The letter is a self-mailer that is not prepared according to DMM 201.3.14.
- Booklet: The letter is a booklet that is not prepared according to DMM 201.3.16.
If your letter meets any of the above conditions, we recommend configuring your shipment in Postsale so that it specifies the non-machinable condition. This helps to ensure that the shipment is handled correctly by USPS and may help to avoid additional USPS surcharges. Here's how:
- Expand the USPS section in the Dock.
- Check the box for the correct non-machinable condition.
