How do I measure for dimensions of a new storm door?

Do I measure inside the frame? Most doors on the website show as being 32" and 36" doors. Is this an inside measurement, or is this the measurement of the width of the outside frame?

From the outside looking in - find the dimensions from the inside edges of the entry door's brick molding (see illustration above). This is where your storm door will attach - the brick molding.

Subtract about one inch from the width of the opening to arrive at the door width size. Any difference in the opening size can be easily adjusted and compensated for when you install the storm door frame.

Measure the door opening height from top to bottom of the doorway (C), and the width at the top (A1), center (A2) and bottom (B3). If the width measurements vary, use the smallest measurement for specifying door size.
http://www.petdoors.com/how_to_measure.h...

The easiest way is to simply measure the entry door itself.

When you install the door you will most likely have to cut the verticle jambs to fit.
The door has an adjustable bottom rail that you will then raise to the correct threshold height.
Be sure you know the measurements of the storms handle so that you can avoid hitting the knob of your antry door.

You measure the frame from the inside because you want to make sure that the door fits. The frames that come with the doors can be trimmed.

Trimming the piece with the striker plate is the most important. It's important that you trim the excess from the bottom, not from the top.

With a Tape Measurer.

Follow the Screen Door Guide at your local Home Improvement store.

They usually have a tear off sheet with detailed step by step info - call and ask??