(2x4 to 2x4 , Floor or jamb to the header) in the house.
Standing Outside and looking at the door if the hinges are on the left it is a Left Hinge else it's a Right Hinge
All measurements are in inches.

There are 3 main types of Storm Doors. Three Hinge,  Four Hinge,   And Residential  Flush-Mount

 
Standard 3 or 4 Hinge        Residential Flush-Mount
 

Standard measured  widths for 3 & 4  Hinge Storm Doors are:  32  34  35-1/2  36  38 
Standard measured heights are:  71-1/2  75-1/2  77-1/2  79-1/2  81-1/2
The Call Size for a 3 or 4 Hinge Storm Door is the measured width + 2 and the measured height + 1/2
So, a door that measures 32x75-1/2 with 4 hinges on the right (outside) would be a Call Size 34x76 Right 4 Hinge

Standard measured widths for Residential Flush-Mount are:   31-1/4  35-1/4  
Standard measured heights for Residential Flush-Mount are:  74-1/4  78-1/4  80-1/4
If your measured width & height both closely match those above your door is a Residential Flush-Mount
For the Call Size add 2-3/4in. to the width and 1-3/4in. to the height
So, a door that measures 35-1/4 x 78-1/4 with the hinges on the left (outside) would be a Call Size 38x80 Left Hinge  Residential

  If your door does not match these measurements to within 1/8 in. it is most likely not a Mobile Home Combo Door.