If you keep your car on the street instead of in a garage, making sure you’re not parked too close to a fire hydrant will likely be one of your most frequent headaches.
Hydrant laws vary by city, but in New York (where I street park my car), you need to be at least 15 feet away—which you can estimate as about one car length. If it looks like there’s enough space for a car to park between you and the hydrant, you’re probably not going to get a ticket. Maybe.
But if you’d rather definitively ensure that you’re actually parked the proper distance away—and in the process, guarantee that you have proof in case you get an erroneous ticket—always use the measurement app on your phone. Set one dot to the hydrant, one dot to your rear wheel or bumper, and make sure it is at least the proper distance away. Take a screenshot, and save it until you move your car out of its parking space, presumably ticket-free.