Most homes have a standard sized hinge of 3.5" x 3.5" This measurement is from the bottom edge of the hinge to the top end of the hinge, and then from the outside edge to edge when the hinge is open. Exterior doors usually have a 4" hinge on them, but not always.
How can I determine the radius of the Door Hinges I need to replace?
The radius of the door hinges will vary. Most common seems to be 5/8" radius, but 1/4" radius corners are common as well. The best way to determine what radius you have is by the following technique. Place a quarter in the corner of the door hinge. If the radius of the quarter is roughly the same as the quarter, you have a 5/8" round. If you do the same with a dime and the radius is similar it is a 1/4" round corner hinge. If there is no radius, you'll need to order a square corner hinge.
How many hinges do I need for my door ?
If you are replacing your door hinges, the answer to this is easy of course. Just replace as many as you have. If you are getting new doors then you may have some options. Most standard sized hollow core interior doors use 3 3.5" hinges. Exterior steel doors, like a Thermatru insulated steel door, would require 3 4" hinges most of the time. The best thing to do is check with your local door shop that is building your doors. They should be able to tell you what size and number of hinges you will need to support the doors you will be installing. Larger than standard sized doors will likely require additional or larger door hinges.
https://www.degolhardware.com/DH1007-Adjustable-Heavy-Duty-Stainless-Steel-Welding-Door-Closer-Flag-Hinge-pd40577985.html
