USDOT number marking rules, in plain English
The FMCSA sets clear rules for how your USDOT number has to appear on a commercial vehicle (see FMCSA §390.21). Get it wrong and you risk a violation at a roadside inspection. Here's what actually matters.
The core requirements
Your USDOT number must be:
- Displayed on both sides of the self-propelled vehicle (the power unit)
- In a color that sharply contrasts with the background
- Readable from 50 feet away in daylight
- Marked with the letters “USDOT” immediately before the number (e.g., “USDOT 1234567”)
- Kept legible and maintained — no fading, peeling, or dirt covering it
How big do the letters need to be?
There's no single federal number for letter height — the rule is functional: legible from 50 feet. In practice, 2-inch letters are the accepted standard and meet the rule on most trucks and vans. Bigger vehicles read better with taller lettering.
- 2 inch — standard for most trucks, vans, and pickups
- 3 inch — larger trucks and better distance visibility
- 4 inch — box trucks, semis, and tall cab or panel doors
Common mistakes that get flagged
The usual culprits at inspection:
- Number on only one side of the vehicle
- Low-contrast lettering (white on a light truck, etc.)
- Magnetic signs that fall off or aren't allowed for your operation
- Faded, cracked, or partially peeling decals
- Missing the “USDOT” prefix, or wrong/old number
The easy way to get it right
We cut every USDOT decal to these specs by default — 2-inch minimum, high-contrast color, “USDOT” prefix, set of 2 for both sides — on commercial-grade outdoor vinyl rated for 5+ years. Tell us your state and vehicle and we'll match your requirements.
General FMCSA guidance shown; verify current federal and your state's intrastate requirements for your operation.
Get USDOT decals cut to spec
2-inch minimum, high-contrast, set of 2 — road-legal and ready to apply.
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