How Long does Flat Rate Shipping Take?

Monday, Nov 14th 2022
postal worker with stack of mail

Before you read any further, understand that there is no guaranteed time when your mail will be delivered. Priority Flat Rate shipping, as far as saving money and time goes, is the best option for satisfying both criteria. Because of this, it is also one of USPS’s most popular class types of mail. 

Firstly, we suggest you start with learning what ‘Flat Rate’ means and how flat rate shipping works. From there, you will better understand why your flat rate mail may (possibly) take more time than initially projected.

What is Flat Rate Shipping?

When someone says ‘Flat Rate’ they’re referring to the consistent, baseline rate charged to ship a package. 

Flat Rate is the least-complicated shipping method.

Many individuals choose it because Flat Rate Shipping is the mail class type that is often described as having the best value. Its delivery is fast, it is cost-effective, and senders will know the exact cost of shipping in advance of arriving at the post office. 

When people refer to ‘Flat Rate Shipping’ or ‘Priority Mail Flat Rate’, they usually mean USPS Priority Flat Rate Shipping. 

The box you choose will match to a consistent price – no more trouble having to calculate the price of your package or box. Flat Rate is an ideal shipping option for businesses as they will be able to forecast their costs. 

For other class types of mail, the weight is calculated into the price. With Flat Rate Shipping, the exact weight of the package does not matter – as long as it is under 70 lbs. 

How Does Flat Rate Shipping Work?

For mail to qualify for the Flat Rate, the package or box you ship your mail in must fit within the size standards/dimensions listed below.

The simplest way to make sure your package meets the Flat Rate size qualifications is to use one of the USPS Flat Rate Envelopes or Boxes (information displayed above). These can be purchased at your local USPS post office. 

Free Supplies Dimensions
Flat Rate Envelope 12 1/2" x 9 1/2"
Small Flat Rate Envelope 10" x 6"
Padded Flat Rate Envelope 12 1/2" x 9 1/2"
Legal Flat Rate Envelope 15" x 9 1/2"
Small Flat-Rate Box Outside: 8 11/16" x 5 7/16" x 1 3/4"
Inside: 8 5/8" x 5 3/8" x 1 5/8"
Medium Flat Rate Box - 1 (top-loading) Outside: 11 1/4" x 8 3/4" x 1 3/4"
Inside: 11" x 8 1/2" x 5 1/2"
Medium Flat Rate Box - 2 (side-loading) Outside: 14" x 12" x 3 1/2"
Inside: 13 5/8" x 11 7/8" x 3 3/8"
Large Flat-Rate Box Outside: 12 1/4" x 12 1/4" x 6"
Inside: 12" x 12" x 5 1/2"

Note: you can put a package or box inside the USPS Flat Rate Box you choose. 

If you were sending a parcel, such as a pair of sneakers, for example, you may decide to put the shoe box (with the shoes inside) inside of the USPS Flat Rate Box. The weight of the entire box must be under 70 lbs.

USPS Flat Rate Shipping Time

Flat Rate shipping typically takes one to three days to arrive at the destination – excluding Sundays or certain holidays. All flat rate shipping will be processed as USPS Priority Mail. 

1 – 3 days is the estimated delivery date. The majority of mail pieces sent through Priority Flat Rate shipping will arrive at their destination within this time frame, but some may not.

From the starting point and ending point – where the mail is sent and where its destination is – are shipping zones. These range from a ‘zone 1’ (local) to a ‘zone 9’ (far away). 

USPS pledges to have all Priority Flat Rate mail delivered within the 1 – 3 day time frame, regardless of what zone the mail’s destination is in. But the farther away the zone is, the more unpredictable variables the mail will confront. 

From its starting point to its destination, mail rarely goes in one trip. It will often change hands along the way – one truck will take it to another post office, where it will be scanned, and then another driver will take it to the next. 

Variables – or causes for a delay – may include slow traffic, processing errors, or more generally busy mailing periods.

Busy mailing periods can be random, but some you can predict. Certain times of the year are expected to be busier than others. 

Christmas (December), for instance, is a time where (literally) millions of mail pieces are processed. During this time, it should not come as a surprise if your Priority Flat Rate mail takes longer than 3 days.

If you require faster delivery, we suggest Priority Mail Express (1 – 2 day delivery). Visit: https://www.usps.com/ship/priority-mail-express.htm.

Flat Rate Shipping Prices

In the table below, you will find the price for the mail size you wish to send. We have included more envelope and box options than in the table displayed above in ‘How Does Flat Rate Shipping Work?’

Free Supplies Shipping Price Dimensions
Flat Rate Envelope $7.75 Commercial Base
$8.95 at Post Office & Online
12 1/2" x 9 1/2"
Window Flat Rate Envelope $7.75 Commercial Base
$8.95 at Post Office & Online
10" x 5″
12 1/2" x 9 1/2"
Small Flat Rate Envelope $7.75 Commercial Base
$8.95 at Post Office & Online
10" x 6"
Padded Flat Rate Envelope $8.45 Commercial Base
$9.65 at Post Office & Online
12 1/2" x 9 1/2"
Legal Flat Rate Envelope $8.05 Commercial Base
$9.25 at Post Office & Online
15" x 9 1/2"
Small Flat-Rate Box $8.25 Commercial Base
$9.45 at Post Office & Online
Outside: 8 11/16" x 5 7/16" x 1 3/4"
Inside: 8 5/8" x 5 3/8" x 1 5/8"
Medium Flat Rate Box - 1 (top-loading) $14.25 Commercial Base
$16.10 at Post Office & Online
Outside: 11 1/4" x 8 3/4" x 1 3/4"
Inside: 11" x 8 1/2" x 5 1/2"
Medium Flat Rate Box - 2 (side-loading) $14.25 Commercial Base
$16.10 at Post Office & Online
Outside: 14" x 12" x 3 1/2"
Inside: 13 5/8" x 11 7/8" x 3 3/8"
Large Flat-Rate Box $19.20 Commercial Base
$21.50 at Post Office & Online
Outside: 12 1/4" x 12 1/4" x 6"
Inside: 12" x 12" x 5 1/2"

For more Flat Rate mail supplies – different types of boxes and envelopes – visit https://www.usps.com/ship/priority-mail.htm.

Despite its occasional delays, the USPS is a miracle of efficiency. To deliver mail in a shipping network as vast and complex as the United States in 1-3 days is truly impressive. 

As times change, and the world of e-commerce becomes the new standard, the USPS will occasionally fall short. But chances are high that your Flat Rate mail will arrive, safe and sound, within the 1-3 day time frame.