What a USDOT number is
The U.S. Department of Transportation number is the primary key for a federal motor carrier record. Treat it like an account number, not a marketing line.
The identifier
FMCSA assigns a USDOT number to entities that are required to register. Household-goods movers operating in interstate commerce are in that universe.
On an estimate it may appear as “USDOT 1234567” or “U.S. DOT No.” If it is missing, ask for it in writing.
Related identifiers
MC, FF, and MX dockets are operating-authority identifiers. A company may have a USDOT without a household-goods docket you expected. Record both. Do not assume they are interchangeable.