A standard curbside mailbox is about 19 inches long, 6 to 7 inches wide and 8 to 9 inches tall outside. That is the classic "T1" size. The larger T2 runs about 23 inches long, 11 inches wide and 13 inches tall. Today's USPS standard no longer fixes sizes: an approved box just has to swallow a test gauge of 18.5 x 5 x 6 inches, or 16 x 13 x 7 inches for large-capacity models.
So "standard" covers a range, and the right size depends on how much mail and how many small parcels you get. If you regularly come home to packages on the porch, a large mailbox is the easy fix. Below are the official size classes, real dimensions of boxes we sell, and how cluster and apartment compartments compare.
Standard mailbox size at a glance
| Size | Approximate dimensions (L x W x H) | Holds |
|---|---|---|
| Standard / T1 / No. 1 | About 19 x 6.5 x 8.5 in. | Letters, catalogs, magazines rolled |
| Medium / No. 1A | About 21 x 8 x 10.5 in. | Flat magazines, padded envelopes |
| Large / T2 / No. 2 | About 23.5 x 11.5 x 13.5 in. | Small boxes and soft packs |
| USPS "Next Generation" package box | About 16.5 deep x 13.63 wide x 12 in. tall at center | Several small packages plus mail |
The first three rows come from the No. 1, No. 1A and No. 2 sizes USPS specified in 1953 and 1954, and are still roughly how the trade describes boxes. The last row is from the USPS package mailbox page, which notes models vary slightly by manufacturer. Exterior sizes vary by a half inch or more between brands, so always check the listing.
What T1, T2 and T3 actually mean
You will see "T1" and "T2" on a lot of mailbox listings. They are traditional size designations from USPS history, not the current rulebook: today USPS-STD-7C defines the requirements.
| Era | Size names | Minimum interior (L x W x H) |
|---|---|---|
| 1992, USPS-STD-7A | T1 / C1 | 18.5 x 5 x 6 in. |
| 1992, USPS-STD-7A | T2 / C2 | 19.5 x 6 x 7 in. |
| 1992, USPS-STD-7A | T3 / C3 | 22.5 x 8 x 11.5 in. |
| 2001, USPS-STD-7B | Fixed sizes dropped; a range allowed | Must accept an 18.5 x 5 x 6 in. gauge |
| 2015, USPS-STD-7C (current) | T, C, LC, LMS, LLC design types | 18.5 x 5 x 6 in. gauge, or 16 x 13 x 7 in. for LC and LLC |
Source: USPS's own curbside mailbox size chronology and USPS-STD-7C. Note that in the trade "T1" and "T2" usually mean the 1953 small and large exterior sizes, not the 1992 interior minimums, which is why numbers online disagree.
The current design types
- T (Traditional): the tunnel shape, must fit the 18.5 x 5 x 6 inch gauge.
- C (Contemporary): any other shape, same gauge, within the traditional maximum size.
- LC (Large Capacity): must fit a 16 x 13 x 7 inch gauge, roughly a shoebox lying flat.
- LMS (Locked, mail slot): a locking box with a slot at least 1.75 inches high and 10 inches wide.
- LLC (Locked, large capacity): a locking box that takes the big gauge and passes USPS security testing.
All of them must carry "Approved by the Postmaster General" to be used curbside. Browse USPS approved mailboxes by size, or read the full USPS mailbox requirements.
Real mailbox dimensions: models we sell
Here are exterior dimensions from our product pages, so you can see how real boxes compare with the "standard" numbers.
| Mailbox | Type | Dimensions | Notes |
|---|---|---|---|
| Whitehall Capitol Mailbox | Non-locking, cast aluminum | 9.7 H x 13 W x 20.4 D in. | Whitehall calls it 20% larger than a standard box |
| Mail Boss Mail Manager | Locking, curbside | 11.25 H x 10.75 W x 21 D in. | Incoming slot takes items up to 3.5 x 10.2 in. |
| Mail Boss Package Master | Locking, curbside | 16 H x 12 W x 21.5 D in. | Small packages up to about 4.5 x 4.5 x 10.5 in. |
| Salsbury Mail Package Drop | Locking, curbside | 14.375 W x 36 H x 23 D in. | Front and rear access; 50 lb |
| Mail Boss Metro | Locking, wall or post | 14.75 H x 15.4 W x 7.15 D in. | Slim wall profile |
Two things jump out. First, depth barely changes: almost every curbside box is 20 to 23 inches deep because the carrier reaches into it from a car. Width and height are where capacity comes from. Second, a locking box's real limit is the slot, not the inside. The Mail Boss Mail Manager has plenty of room inside, but anything thicker than its 3.5 inch slot will not get in. If you want parcels secured, step up to something like the Mail Boss Package Master, which Mail Boss rates for small packages up to about 4.5 x 4.5 x 10.5 inches.
How to choose the right mailbox size
- Count a normal week. If your mail fits in a standard box every day with room left, a standard size is fine.
- Count your packages. Small boxes and padded mailers several times a week point to a large or package mailbox.
- For locking boxes, check the slot. USPS requires a slot big enough for your normal daily mail. Compare slot height against the thickness of your usual parcels.
- Check the post or wall. A large box is heavier and wider. Make sure your post, arm or wall can carry it, and that the box still lands 41 to 45 inches above the road. See how high a mailbox should be.
- Check local rules. HOAs sometimes cap mailbox size or require a specific model.
For parcels specifically, see our package mailbox collection, or the full guide on choosing a mailbox for packages.
Wall-mounted mailbox sizes
Wall boxes are shallow and wide instead of long, because the carrier drops mail in from above or through a front slot. The Mail Boss Metro above, for example, is only 7.15 inches deep. USPS has no size standard for a single-home wall box and does not require the PMG seal on one, so size is about your mail volume and the wall space next to your door.
Cluster mailbox (CBU) dimensions
Cluster box units are sized by how many doors and parcel lockers they hold, labeled Type I to VI. Here is how the Salsbury units we carry are configured:
| CBU type | Customer doors | Parcel lockers |
|---|---|---|
| Type I | 8 | 2 |
| Type II | 12 | 1 |
| Type III | 16 | 2 |
| Type IV | 13 | 1 |
| Type V | 4 | 2 |
| Type VI | 8 | 4 |
As one example, the Salsbury Type II CBU (12 doors, 1 parcel locker) is listed at 30.5 W x 62 H x 18 D inches and 155 lb. Salsbury lists its customer doors at 12-3/4 inches wide in three heights (3-1/8, 4-7/8 and 6-3/4 inches) and parcel locker doors at 12 inches wide by 10 or 13-1/2 inches high. For planning a whole site, see our cluster mailbox buying guide.
4C apartment mailbox compartment sizes
Apartment and commercial mailboxes built to USPS-STD-4C use horizontal compartments. USPS-STD-4C sets the minimum customer compartment at 3 inches high by 12 inches wide by 15 inches deep, much roomier than the old narrow 4B-style slot. Mounting rules are covered in the USPS-STD-4C drawings: no customer compartment below 28 inches and no tenant lock above 67 inches from the floor.
"It is bigger than I expected"
Customers do tell us this. One Whitehall buyer called theirs gigantic. Product photos have nothing around them for scale.
Before you order, tape the footprint on the post or wall, or cut it from a cardboard box. A Mail Boss Mail Manager is 11.25" high, 10.75" wide and 21" deep, which is much bigger than an older T1 box. Size matters more if the box is custom. Personalized plaques and monograms cannot be returned for a refund, even when the mailbox itself can.
Shop by size
Browse the large mailbox collection for package-friendly boxes. Unsure what will fit your post? Contact us with your current setup and we will help you size it.
Mailbox size questions
Are mailboxes this large normal now?
Locking boxes are larger than the old steel curbside box because they need a secure compartment and room for small parcels. If space is tight, compare the dimensions in the table above before you decide.
What is the standard size of a mailbox?
The classic standard (T1) curbside box is about 19 inches long, 6.5 inches wide and 8.5 inches tall outside. Current USPS rules only require that it fits an 18.5 x 5 x 6 inch test gauge.
What is the difference between a T1 and T2 mailbox?
Size. A T1 is the standard box, about 19 x 6.5 x 8.5 inches. A T2 is the large one, about 23.5 x 11.5 x 13.5 inches, with room for small parcels. Exact sizes vary by brand.
What size mailbox do I need for packages?
Look for a large-capacity box that fits USPS's 16 x 13 x 7 inch gauge, or a package mailbox. On locking boxes, check the slot or package door size, not just the inside.
Are large mailboxes USPS approved?
Many are. USPS-STD-7C has a Large Capacity class for non-locking and locking boxes. Look for "Approved by the Postmaster General" on the door, or check the approved list.
How big is a cluster mailbox?
It depends on the type. For example, a Salsbury Type II CBU with 12 doors and 1 parcel locker is listed at 30.5 inches wide, 62 inches high and 18 inches deep.
******It is always recommended to contact your local postmaster prior to installation. While most of our mailboxes are USPS-approved your local postmaster may have specific preferences in terms of mailbox types and installation location******