If you run a commercial vehicle, 49 CFR 390.21 says your markings have to be right on BOTH sides — and roadside inspectors check. Here is the rule in plain English, verified September 2026.
What the regulation requires
- The legal name or single trade name of the motor carrier operating the vehicle
- The letters USDOT followed by the USDOT number issued to that carrier
- On both sides of the power unit (the truck, not the trailer)
- In letters that contrast sharply with the background
- Legible from 50 feet in daylight while the vehicle is stopped
How big should the letters be?
The federal rule does not name a letter height — it names a distance. Two-inch letters can pass the 50-foot test on a clean door in good light. We cut three inches as standard, because two-inch letters on a dirty door at dusk are exactly the kind of thing an inspector writes up, and the price difference is nothing. We wrote up what the regulation actually says, quoted verbatim with the eCFR link: USDOT number size requirements.
MC numbers and extra lines
Your MC number is not federally required on the door, but most for-hire carriers add it. Add MC, GVW, unit number or NOT FOR HIRE as extra lines in the same contrasting, legible style. Not sure which numbers you need? USDOT vs MC number, explained.
Leased on to someone else's authority?
The door shows their name and USDOT number, not yours. Get the exact spelling from your carrier before you order.
Get compliant
We cut name + USDOT sets from 3M commercial cast vinyl, both sides, three-inch letters, with a to-scale proof you approve before anything is cut. $79 shipped free anywhere in the country, or $195 installed in Spokane, Spokane Valley and North Idaho. Order before 12:00 PM Pacific and your proof comes back the same day. Fleet pricing from two trucks up.
Order a USDOT + MC set — $79, ships free → · Build and price a fleet set · Free fleet quote
JZAC Designs — Spokane Valley, WA. Text a photo of your door to 509-720-8239 for same-day pricing.