For light weight internal doors two 3 butt hinges should be adequate.
Internal door 3 hinge positions.
The top hinge need to be positioned approx.
If they have 3 x 3inch hinges such as a bathroom door where high humidity can sometimes bow the middle if you measure from the top of the door and mark at 6in 36in and 66in positions marking the hinges below these marks and you end up with a perfectly centred hinge 27in between leafs plus the bottom hinge is 9in from the bottom.
170 180mm 6 inches from the top.
Light hollow core doors that are 6 8 only require 2 hinges with a cheap pin.
When a door starts to sag and hang crooked it always does so from the top so the upper part of the doorknob side is where it will start to catch.
Hinges are generally spaced out equally to also keep the door straight.
For the time being fix the hinges in position using one screw in each of the hinge centre fixing holes in case any adjustments have to be made.
Now all the preparation work for fitting the hinges is complete you can either fix the hinges to the door frame or as i prefer fix them to the door edge.
190 200mm 9inches from the bottom.
The top hinge is a little closer to the top usually about 7 as it is always in tension with the forces applied.
Hillman squeak proof 3 1 2 in oil rubbed bronze 5 8 in radius mortise door hinge 3 pack item 953103.
How to hang a new internal door in position.