Did you know that not all postage options can be used with every package type? If an incorrect postage option is used it can lead to additional charges or rate adjustments. Here we will help you understand how to choose the right packaging to get the right postage and your shipment to your customer! 

There are 4 different package types on our platform: Letter, flat envelope, thick envelope and parcel.


The letter package type includes small envelopes, postcards, greeting cards and other rectangular mail pieces that are "machineable." What is "machineable"? It means the package has no bumps, no padding or ridged items like protective cardboard backing. Basically, the Letter package must be made of paper, flexible or bendable and uniform in shape. It must also fall within specific measurements. If you are sending postcards with this postage type make sure they are:

  • Are under the maximum dimensions
  • Do not contain a seal
  • Are not in an envelope

The USPS guidelines for postcards and letters are as follows:

Minimum DimensionsMaximum Dimensions
PostcardsHeight: 3-1/2 inches high
Length: 5 inches long
Width: 0.007 inch thick
Height: 4-1/4 inches high
Length: 6 inches long
Width: 0.016 inches thick
LettersHeight: 3-1/2 inches high
Length: 5 inches long
Width: 0.007 inch thick
Height: 6-1/8 inches
Length: 11-1/2 inches
Width: 1/4 inch
Weight: 3.5 ounces

Additionally, USPS First Class Mail International with letter packaging can only contain documents.

Flat & Thick Envelopes

All envelopes must be machineable or a surcharge may apply. The envelope category can be further divided into flat envelopes and thick envelopes. 

With flat envelopes, carriers will typically only accept documents such as newsletters, magazines and documents in other large envelopes (including flats in courier bags). Whereas, thick envelopes are your standard bubble mailers and other large padded envelopes (e.g. poly or kraft mailers). However, the USPS guidelines for thick envelopes align more closely with their guidelines for parcels–reference the section below for dimensional guidelines. 

First Class Mail postcards, letters and flats are not eligible for USPS tracking. These items are eligible for tracking with other USPS services such as Priority Mail.

Minimum DimensionsMaximum Dimensions
Flat EnvelopesHeight: 6-1/8 inches
Length: 11-1/2 inches
Width: 1/4 inch
Height: 12 inches
Length: 15 inches
Width: 3/4 inch


Parcels refer to standard packaging like your boxes, or irregular parcels like tubes or rolls. The USPS general guidelines for parcels are as follows.

Minimum DimensionsMaximum Dimensions
Machineable ParcelsHeight: 3 inches
Length: 6 inches
Width: ¼ inch
Weight: 6 ounces
Height: 27 inches
Length: 17 inches
Width: 17 inches
Weight: 25 pounds, 35 pounds if Parcel Select

Additional weight and dimension restrictions may depend on the parcel type like irregular parcels like tubes, rolls and triangles or the postage type selected. For example, in order to receive a USPS Priority  rate for your thick envelope, it must adhere to the requirements for cubic pricing. If your shipment does not meet the cubic requirements, we recommend selecting the "parcel" package type instead.

Compatible Postage & Package Types Combinations

Below are all of the combinations of compatible postage and package types on the Chit Chats platform.

LettersFlat EnvelopesThick EnvelopesParcels
Chit Chats Select

Chit Chats Slim

Chit Chats Canada Tracked

Chit Chats Collect 

Chit Chats U.S. Select

Chit Chats U.S. Edge

USPS First Class Mail

USPS Priority Mail

Chit Chats International Tracked

USPS First Class Mail International

USPS First Class Package International

USPS Priority Mail International
USPS Priority Mail Express International*
USPS Media Mail*
USPS Priority Mail Express*

If you are still experiencing issues with getting a postage rate, check that you've entered the weight and dimensions of your shipments and that they are within the allowable limits. When shipping with Chit Chats Canada Tracked, check out these other conditions.

*Service availability may vary, e.g. USPS First Class Mail International service will only accept documents.. Find USPS's additional requirements for Media Mail content here.