| 5 Min Read | Updated June 2026 | The Adoorn Editorial Team |
For most homes, the choice comes down to two sizes: Small or Large. The real question is not the outside dimension. It is how much mail piles up before you get to it, and what you want the box to handle without a trip to the post office.
The Direct Answer
Most residential mailboxes come in two sizes: a Small that holds two to three days of mail, and a Large that holds seven to fourteen. The rule of thumb: choose Small for a single person or couple with everyday mail, and Large if you travel, run a household, or get heavy magazine, catalog, and parcel volume. Both meet USPS standards.
| 01 | What's Standard |
What counts as a "standard" mailbox size
There is no single legal "standard mailbox" dimension, but residential mailboxes cluster into two practical sizes, and that is what most people mean by the question. A standard or Small mailbox is built for everyday letter mail and the occasional padded envelope. A Large mailbox adds height and depth for catalogs, magazines, and small parcels, so things stop getting jammed or left at the door.
For reference, here are Adoorn's actual dimensions:
| Model | External dimensions (H × W × D) |
|---|---|
| Post Mount, Small (locking) | 12" × 12" × 18.5" |
| Post Mount, Large (locking) | 15.5" × 12" × 18.5" |
| Post Mount, Non-Locking | 9.5" × 9.5" × 21" (fits taller parcels up to 16" × 8" × 7.5") |
| Wall Mount, Small (locking) | 13.5" × 15" × 5.5" |
| Wall Mount, Large (locking) | 18.5" × 15" × 7.5" |
Whatever brand you choose, the deciding factor is not the outside dimension. It is how much mail piles up before you get to it, and what you want it to handle without a trip to the post office.
| 02 | Capacity |
What actually fits in each size
Capacity is the real question behind "what size." Here is what each Adoorn size handles:
- Post Mount, Small holds two to three days of mail and takes letter mail, padded envelopes, and parcels up to 16" × 10" × 2".
- Post Mount, Large holds seven to fourteen days of mail with the same 16" × 10" × 2" parcel window, sized for travel and high-volume households.
- Wall Mount, Small holds two to three days of mail plus poly-bag mailers up to about 13" × 12" × 2", mounted at the door.
- Wall Mount, Large holds seven to fourteen days with the same poly-bag window, for porch-delivery homes with heavier volume.
A note on packages: every Adoorn mailbox takes small parcels and mailers, but none is built for large boxes. If you regularly receive boxes, that is a job for a package box, not a bigger mailbox (more on that below).
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| 03 | The Decision |
Small vs Large: the decision in three questions
You do not need to measure anything. Answer three questions and the size is obvious.
- 1How much mail do you get in a week?Mostly letters and the odd envelope points to Small. A steady flow of magazines, catalogs, and padded mailers points to Large.
- 2How big is your household?One or two people rarely outrun a Small. A family, a home office, or anyone juggling multiple senders fills a Small fast and is better served by a Large.
- 3How often are you away?If mail sits for a day or two at most, Small is fine. If you travel, work long days, or leave town for stretches, size up so a few days of mail never overflows or signals an empty house.
If you answered "more" to any of these, go Large. The cost difference is small next to the daily friction of a box that is always full.
| 04 | Side By Side |
Small vs Large, post mount and wall mount
| Post Mount, Small | Post Mount, Large | Wall Mount, Small | Wall Mount, Large | |
|---|---|---|---|---|
| Days of mail | 2–3 | 7–14 | 2–3 | 7–14 |
| Max parcel / mailer | 16″ × 10″ × 2″ | 16″ × 10″ × 2″ | ~13″ × 12″ × 2″ poly-bag | ~13″ × 12″ × 2″ poly-bag |
| Best for | Single or couple, everyday mail | Family or frequent traveler | Porch delivery, single or couple | Porch delivery, family or traveler |
| Locking | Yes | Yes | Yes | Yes |
Both post mount sizes share the same parcel window, so the choice there is purely about how many days of mail you want to hold. On the wall mount, the same logic applies at the door.
| 05 | Form Factor |
Still deciding: post mount or wall mount?
Size is only half the decision. The other half is where your mail actually arrives. If your carrier delivers to the curb, you want a post mount. If your carrier walks to the porch or door, you want a wall mount. If you are not sure which fits your home, that comparison has its own guide.
Ready To Choose?
Here's where to go next
Once you know your size, the right buying guide walks the rest of the decision: finish, color, locking, and install.
- Post mount, modern mailbox overall → The Complete Modern Mailbox Guide
- Post mount, locking specifically → The Best Locking Mailbox Guide
- Wall mount → The Best Wall Mount Mailbox Guide
Backed by 350,000+ Adoorn installs across every climate.
| 06 | For Packages |
When a bigger mailbox is not the answer
If your real problem is boxes, not letters, sizing up the mailbox will not solve it. Mailboxes are built for mail and small mailers. For routine package deliveries, the fix is a dedicated package box that holds parcels until you are home.
| 07 | The Questions |
Frequently asked
What is a standard mailbox size?
There is no single legal standard, but residential mailboxes fall into two practical sizes. A Small or standard box handles everyday letter mail and the occasional padded envelope, while a Large adds depth for catalogs, magazines, and small parcels. Adoorn's Small post mount holds two to three days of mail; the Large holds seven to fourteen. Both meet USPS standards.
What size mailbox do I need?
It comes down to three things: how much mail you get weekly, your household size, and how often you are away. Light mail for one or two people fits a Small. Heavy magazine and catalog volume, a full household, or frequent travel all point to a Large so mail never overflows. When in doubt, size up.
Will a mailbox fit packages?
A mailbox fits small parcels and poly-bag mailers, not large boxes. Adoorn's post mount takes parcels up to 16 by 10 by 2 inches; the wall mount takes poly-bag mailers up to about 13 by 12 by 2 inches. For routine boxes, use a dedicated package box instead of sizing up the mailbox, which is built for mail.
What are standard mailbox dimensions?
Residential mailboxes vary by maker, but Adoorn's give a useful reference: the Small locking post mount is 12 inches high by 12 wide by 18.5 deep, and the Large is 15.5 high by 12 wide by 18.5 deep. The non-locking post mount runs 9.5 by 9.5 by 21 inches. The number that matters most is capacity, not the outside dimension.
Small vs Large: which mailbox should I get?
Choose Small if you are one or two people with everyday mail and you check the box most days. Choose Large if you have a family or home office, get steady magazine and parcel volume, or travel enough that mail piles up. Both share the same locking build, so the decision is about volume, not security.
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Continue Reading · Buying Guide The Complete Modern Mailbox GuideThe hub: form factor, finish, color, locking, and install in one place. |
Continue Reading · For Packages The Best Lockable Package BoxWhen the parcels outgrow the mailbox, here is the box built for boxes. |
Adoorn · modern mailboxes, designed in Chicago.