Place numbers on the right side (flag side) of a curbside mailbox — that's the USPS-preferred position. For maximum compliance and visibility, put them on both sides. Numbers must be at least 1 inch tall and contrast clearly with the mailbox color.
Here's the complete breakdown by mailbox type, what USPS actually requires, and the mistakes that cause missed deliveries.
What USPS Actually Requires for Mailbox Numbers
USPS doesn't regulate font style or material, but it does set clear requirements on placement, size, and visibility. These come from the USPS Domestic Mail Manual and apply to all residential curbside mailboxes.
The four requirements are : numbers must be on the flag side or front of the mailbox, at least 1 inch tall, in a color that contrasts with the mailbox surface, and readable from the street by a carrier approaching at driving speed.
One additional rule that most homeowners miss : if your mailbox is not directly in front of your house — for example, it's shared with a neighbor or offset at a corner lot — you must display the full street address, not just the house number.
📬 Key rule : USPS does not require numbers on both sides, but strongly recommends it for any mailbox accessible from two directions of travel. A carrier who can't read your number from their vehicle is not required to stop. See the full requirements in the USPS Domestic Mail Manual — Section 508.4.
Placement by Mailbox Type
Curbside post-mounted mailbox This is the most common setup and the one with the most specific USPS guidance. Place numbers on the right side (flag side) as the primary location — this is the side facing oncoming traffic in the direction the carrier travels. If your street has two-way traffic with carriers approaching from both directions, place numbers on both sides. The front door of the mailbox is acceptable as a secondary location but not recommended as the only placement — it's harder to read from a moving vehicle.
Wall-mounted mailbox Place numbers on the front face of the mailbox in the largest size that fits cleanly. If the mailbox is small and numbers would be cramped, mount them on the wall directly above or beside the mailbox instead. The key is that they're readable from the street or walkway without the carrier having to approach the door.
Mailbox on a post far from the house If your mailbox is at the end of a long driveway or on a rural road far from your home, place numbers on both sides of the post in addition to the mailbox itself. Reflective numbers are strongly recommended for rural routes where carriers drive at higher speeds.
Cluster Box Units (CBUs) Individual residents do not need to add numbers to CBU compartments — these are pre-labeled and managed by USPS or the property manager. If your unit number has faded or fallen off, contact your property manager, not USPS directly.
⚠️ Corner lots and offset mailboxes If your mailbox is not directly in front of your house number — common on corner lots — USPS requires the full street address (number + street name) on the mailbox, not just the house number. A carrier who can't match your mailbox to your address may skip delivery entirely.
Size, Color and Material — What Actually Works
Size USPS minimum is 1 inch tall. In practice, 2 to 3 inches is significantly more readable from a moving vehicle, especially on rural routes or streets with higher speed limits. If you're replacing numbers, go with 2 inches minimum.
Color contrast This is where most homeowners get it wrong. The contrast must be between the number color and the mailbox surface — not just "different shades." Black on white, white on black, silver on black, or black on silver all work well. Silver on gray, white on cream, or dark blue on black do not — they look fine up close but become invisible at distance or in rain.
Material Reflective vinyl decals are the most practical option — affordable, weather-resistant, and highly visible at night. Metal self-adhesive numbers are more durable for long-term use. Avoid painted-on numbers unless you use a high-contrast, weather-grade paint — standard paint fades within 1-2 seasons in direct sun or harsh climates.
| Placement | When to use | Visibility |
|---|---|---|
| Flag side (right) only | One-way street, carrier approaches from one direction | Good |
| Both sides | Two-way street or rural road | Best |
| Front door only | Wall-mount or when sides aren't accessible | Acceptable |
| Post below mailbox | Never — obscured by grass/snow | Poor |
| Wall above mailbox | Wall-mount with small box | Good |
🏠 Upgrading your mailbox? If your mailbox is old, faded, or too small for number placement, now is the right time to replace it. Our modern mailboxes have flat side panels specifically designed for clean number placement — no curves or recessed surfaces that cause numbers to peel. Available in wall-mount and post-mount from $99 with free shipping.
The 4 Most Common Mistakes
1. Numbers only on the front door The door faces directly toward the house, not toward approaching traffic. A carrier driving past at 15 mph has less than 2 seconds to read your number — front door placement makes this nearly impossible.
2. Numbers too low on the post Numbers placed on the post below the mailbox get covered by snow in winter, obscured by tall grass in summer, and are below the natural sightline of a driver. Always place numbers on the mailbox body itself, not the post.
3. Colors that blend together Brushed silver numbers on a silver mailbox, white numbers on a light gray mailbox — these look fine in photos but become unreadable in overcast light or from a distance. Test yours by standing at the street and reading the number without approaching.
4. Numbers on the non-flag side only The left side of a curbside mailbox typically faces away from the carrier's direction of travel. A carrier who can't see your number from the right side may mark your address as unreadable.
🔒 While you're upgrading your numbers If your mailbox is already taking attention, consider adding a mailbox lock at the same time. A locking mailbox with clearly placed numbers is the complete setup — your address is visible, your mail is secure. Replacement cam locks from $14.90 fit most standard residential mailboxes.
Visibility at Night and in Low Light
USPS carriers on rural routes often deliver in early morning darkness or late afternoon in winter. Standard painted or vinyl numbers become very difficult to read in those conditions.
Reflective vinyl numbers are the simplest upgrade — they bounce headlights back to the driver and are readable at 50+ feet in darkness. They cost the same as standard vinyl and install identically.
Solar mailbox lights mount above the mailbox and illuminate the number area automatically at dusk. Most models cost $15-30 and require no wiring — a worthwhile investment for any address on a poorly lit street.
Reflective address signs on a separate post are the strongest option for rural properties — a 4x12 inch reflective green sign with white numbers is visible from 200+ feet in headlights, which is why they're standard on rural 911 addressing systems.
FAQ
Where should I put numbers on a mailbox according to USPS? USPS recommends the flag side (right side) of a curbside mailbox as the primary location. Numbers must be at least 1 inch tall and contrast clearly with the mailbox color. For two-way streets, place numbers on both sides.
Can I put my house number on the mailbox post instead of the mailbox? Numbers on the post are acceptable as a supplement but not as a replacement. Post-mounted numbers are often obscured by grass, snow, or vehicles. Always put numbers on the mailbox body itself as the primary location.
How big should mailbox numbers be? USPS minimum is 1 inch. In practice, 2 to 3 inches is significantly more readable from a moving vehicle. For rural routes or high-speed roads, use the largest size that fits cleanly on the mailbox surface.
What color should mailbox numbers be? Any color that strongly contrasts with the mailbox surface — black on white, white on black, silver on black. Avoid similar shades like silver on gray or white on cream, which become unreadable in low light or rain.
Do I need numbers on both sides of my mailbox? USPS doesn't require it but strongly recommends both sides for any mailbox on a two-way street or rural road. If a carrier can't read your number from their vehicle, they are not required to stop.
What's the best material for mailbox numbers? Reflective vinyl decals offer the best combination of visibility, durability, and cost. They're readable at night, weather-resistant, and available at any hardware store for under $10.
What if my mailbox is on a corner lot? If your mailbox is not directly in front of your house address, USPS requires the full street address (number + street name) on the mailbox — not just the house number. This helps carriers match your box to the correct address on their route.
