USPS Priority Mail Box Selector
Enter your item's dimensions in inches to find which USPS Priority Mail boxes fit. This tool helps you avoid overpacking fees and save on shipping costs.
When you need something shipped fast-like a birthday gift, a replacement part, or an important document-USPS Priority Mail is one of the most reliable options for next-day or two-day delivery across the U.S. But if you’ve ever stood in front of a USPS counter wondering which box to pick, you’re not alone. The right box isn’t just about fitting your item. It’s about cost, speed, and avoiding extra fees. So what sizes does USPS actually offer for Priority Mail?
USPS Priority Mail Box Sizes: The Official Options
USPS doesn’t let you just use any box for Priority Mail. They offer free, pre-sized boxes designed specifically for this service. These aren’t just any cardboard boxes-they’re engineered for durability, stacking, and efficient sorting. And yes, they’re free. You can pick them up at any Post Office, or order them online for delivery to your door.
As of 2025, USPS offers seven standard Priority Mail boxes. Each has fixed dimensions and is meant for specific types of items. Here’s the full list:
- Priority Mail Small Flat Rate Box - 8 11/16" x 5 7/16" x 1 3/4"
- Priority Mail Medium Flat Rate Box (1) - 11" x 8 1/2" x 5 1/2"
- Priority Mail Medium Flat Rate Box (2) - 13 5/8" x 11 7/8" x 3 3/8"
- Priority Mail Large Flat Rate Box - 12" x 12" x 5 1/2"
- Priority Mail Regional Rate Box A - 12" x 10" x 5 1/2"
- Priority Mail Regional Rate Box B - 14" x 12" x 6"
- Priority Mail Large Flat Rate Box (2025 update) - 18" x 12" x 6" (newer, larger option)
These aren’t just random sizes. They’re based on how packages move through USPS sorting centers. The flat rate boxes are the most popular because you pay one price no matter how far it goes-whether it’s across town or across the country. The Regional Rate Boxes are cheaper for shorter distances within specific zones.
Flat Rate vs. Regional Rate: What’s the Difference?
It’s easy to confuse these two types. Flat Rate means the price stays the same no matter where you ship it. For example, a Medium Flat Rate Box costs $15.60 in 2025 whether it’s going to Alaska or Florida. That’s great if you’re shipping something heavy or dense.
Regional Rate Boxes, on the other hand, are priced based on distance. They’re cheaper for short hauls-like shipping from Chicago to Milwaukee-but get more expensive as the distance increases. If you’re sending something light and bulky, like a pillow or a set of books, and it’s going less than 300 miles, Regional Rate can save you money.
Here’s a quick comparison:
| Box Type | Dimensions (inches) | Price (2025) | Best For |
|---|---|---|---|
| Small Flat Rate | 8.6 x 5.4 x 1.75 | $9.35 | Jewelry, small electronics, documents |
| Medium Flat Rate (1) | 11 x 8.5 x 5.5 | $15.60 | Books, clothing, toys |
| Medium Flat Rate (2) | 13.6 x 11.9 x 3.4 | $15.60 | Shoes, bulkier items |
| Large Flat Rate | 12 x 12 x 5.5 | $21.50 | Board games, kitchenware, small appliances |
| Large Flat Rate (2025) | 18 x 12 x 6 | $24.75 | Larger electronics, multiple items |
| Regional Rate A | 12 x 10 x 5.5 | $11.95-$17.75 | Light items under 300 miles |
| Regional Rate B | 14 x 12 x 6 | $14.65-$21.95 | Medium-weight items under 500 miles |
Notice something? The Flat Rate boxes are priced the same nationwide. The Regional Rate boxes vary. That’s why most small businesses and online sellers stick with Flat Rate-it’s predictable. If you’re shipping 10 packages a week, you know exactly what your postage will cost.
Can You Use Your Own Box for Priority Mail?
You can. But there’s a catch. If you use your own box, you can’t use the Flat Rate price. You’ll be charged based on weight and distance-just like Priority Mail Parcel. That means you’ll need a scale and to know your recipient’s ZIP code to calculate the cost.
Here’s when using your own box makes sense:
- Your item is very light (under 1 pound)
- You’re shipping to a nearby zone (Zone 1-3)
- You have a custom-shaped item that won’t fit in a USPS box
But if your item weighs more than 2 pounds or you’re shipping across the country, you’re almost always better off using a USPS Flat Rate box. Why? Because the cost is fixed, and you avoid surprise fees. One customer in Ohio shipped a 5-pound box of tools using his own box and got charged $28. He could’ve used a Medium Flat Rate Box for $15.60 and saved over 40%.
What Happens If Your Item Doesn’t Fit?
USPS has rules. If you try to overstuff a Flat Rate box, they’ll reclassify it as a weight-based package and charge you the difference. That’s expensive. If you’re close to the edge, measure carefully.
Here’s a simple rule: If you can close the box with a single piece of tape and the flaps lie flat, you’re good. If you’re forcing the flaps shut or the box bulges, it’s too full. USPS scanners will catch it at the sorting center.
For oversized items-like a large lamp or a bike seat-your best bet is Priority Mail Large Flat Rate Box (2025 version) or a custom box with Priority Mail Parcel service. You’ll pay by weight, but you’ll still get 1-3 day delivery.
How to Get Free USPS Priority Mail Boxes
They’re free. Seriously. No strings. No purchase required. You can pick them up at any Post Office-just ask the clerk. Most locations keep them stacked near the counter.
Or, if you’re tired of driving, order them online:
- Go to usps.com/shop
- Search for "Priority Mail boxes"
- Select the type and quantity
- Enter your address
- They’ll arrive in 2-3 business days
You can order up to 500 boxes at a time. That’s why e-commerce sellers use this method to stock up before holiday seasons.
Pro Tips for Using USPS Priority Mail Boxes
- Don’t reuse old boxes - If the box has old labels, tape, or damage, USPS may reject it. Use new ones.
- Use packing peanuts or crumpled paper - Even in Flat Rate boxes, items can shift. Cushion fragile things.
- Label clearly - Write "Priority Mail" on the box if you’re hand-delivering it. Helps avoid delays.
- Track everything - Every Priority Mail box comes with a tracking number. Save it. If your package goes missing, you’ll need it.
- Ship early - If you need next-day delivery, drop it off before 2 p.m. local time. After that, it goes out the next day.
What About Speed? Is Priority Mail Really Next-Day?
USPS guarantees delivery in 1-3 business days for Priority Mail. But "next-day" isn’t guaranteed nationwide. It depends on where you’re shipping from and to.
Here’s the reality:
- Within the same metro area? Often next-day.
- From New York to Los Angeles? Usually 2 days.
- From rural Maine to rural Arizona? Could be 3 days.
USPS doesn’t promise next-day delivery like FedEx or UPS overnight. But for the price-starting at $9.35-it’s one of the fastest and cheapest options for non-urgent but important items.
What’s the Best Box for Online Sellers?
If you run a small online store, the Medium Flat Rate Box (1) is your best friend. It holds 10-15 books, 5-8 shirts, or a pair of shoes with padding. It’s the sweet spot: big enough for most items, small enough to keep shipping costs low.
Many sellers use the Small Flat Rate Box for accessories and the Large Flat Rate Box for bundled orders. The new 18x12x6 box is gaining traction for customers who buy multiple items at once.
Pro tip: Print your own labels online. You get a discount-about 10% off retail prices. And you can schedule pickup so the carrier comes to you.
Can I use Priority Mail boxes for regular mail?
Yes, you can use Priority Mail boxes for First-Class Mail or Parcel Select, but you won’t get Priority Mail speeds or tracking unless you pay for Priority Mail service. The box itself doesn’t determine the service-it’s the label you put on it.
Do USPS Priority Mail boxes have weight limits?
Yes. Flat Rate boxes have a maximum weight of 70 pounds. That’s the legal limit for any USPS package. Most items you ship won’t come close, but if you’re sending heavy tools or books, weigh them first. Exceeding 70 pounds means you’ll need to use a different service.
Are USPS Priority Mail boxes waterproof?
No. The boxes are made of standard corrugated cardboard. If you’re shipping something that can’t get wet-like electronics or documents-add a plastic bag or waterproof liner inside. Don’t rely on the box alone.
Can I ship liquids in a Priority Mail box?
Yes, but only if they’re non-hazardous and properly sealed. Liquids must be in leak-proof containers, surrounded by absorbent material, and packed so they can’t shift. USPS requires extra packaging for liquids-don’t just pour shampoo into a bottle and toss it in a box.
What if my Priority Mail package is late?
USPS doesn’t offer a money-back guarantee for Priority Mail like FedEx or UPS does. But if your package is significantly delayed-say, over 3 business days-you can file a claim for lost or damaged items. Tracking helps, but refunds aren’t automatic. Always insure valuable items.
Final Thoughts: Pick the Right Box, Save Money
USPS Priority Mail boxes aren’t just convenient-they’re cost-effective. The right size saves you from overpaying. The wrong size can cost you extra in shipping fees or damaged goods.
For most people, the Medium Flat Rate Box is the go-to. For small items, go Small. For bulky or multiple items, go Large. Always use the free boxes. Always track your package. And always ship early if you need it fast.
Next time you’re packing something for delivery, don’t guess. Grab the right box. You’ll save time, money, and stress.
