Anyone who owned a drone before Dec. 21 will be required to register a machine by Feb. 19, 2016. People who get a drone after Dec. 21, which includes anyone who receives a drone over Christmas, will be required to register before their first flight. There will be an option for owners to register by mail or in person, and the rules apply only to people over the age of 13, though children are permitted to fly under a parent’s registration.

The users are then required to put their registration numbers on any drone they own and have their registration card on them when they take a drone out for a flight.

Many questions remain on how the rules will be enforced and how consumers will be informed, though the F.A.A. said it would promote the new rules online and work with retailers and hobby groups to inform the public.

“I’m sure retailers and others are scrambling right now,” Ms. Ellman said.

Drone manufacturers and hobby groups have warned that the $5 for registration in the United States will harm their businesses and discourage new users. But the F.A.A. said it was necessary to charge a fee to cover the costs of running the database.

Critics of the registration said the minimum weight of half a pound — the equivalent of two sticks of butter — would include too many small toy drones that are most popular with children and are generally harmless.