Vehicle codes vary between state, however, a parking distance between 10 and 15 feet from a fire hydrant is common, as shown by the Department of Motor Vehicles websites for California, Connecticut and New York. Legal distance can be determined by verifying with a particular state's DMV or equivalent agency.
California's Vehicle Code states that a vehicle must not be left within 15 feet of a fire hydrant, yet the code allows for exceptions, according to the California DMV. A vehicle may park in front of a hydrant as long as a licensed driver is in the driver's seat. The law also allows for local ordinance to modify the parking distance.
New York's DMV notes a similar policy that restricts parking near a fire hydrant to a distance of 15 feet, unless a licensed driver is in the driver's seat and moving the vehicle for an emergency. According Connecticut DMV's online manual, the legal distance is 10 feet.