Finder Venus Ellis was at her mother's home when she made the discovery in February last year, Wakefield Coroner's Court was told during a treasure inquest today.
She began searching the garden using her son's metal detector, after losing a bolt from a grass strimmer.
The detector bleeped, but as she scoured the ground she could not find the part.
Intrigued, she began digging and after about six to eight inches, uncovered several small, silver-bronze coins.
She continued to dig and unearthed 17 coins in total.
Andrew Parker, estate manager at Wakefield District Housing, said he had been made aware of the discovery and that the finder had permission from the house's tenant to be on the property.
The hoard was referred to the British Museum.
A report from the institution said the find was made up of 17 Roman copper alloy coins, known as nummus.
They are believed to date back to 335AD-402AD.
Senior coroner David Hinchliff declared the coins to be treasure.
The court was told Wakefield Museum had expressed an interest in acquiring them.