Start with the inside mount. For an inside mount, measure in three positions to make sure the plan is square: Top, middle, and bottom.
Next, a bracket-to-bracket measurement will be done for this shade, which is to fit inside the window at 31″, leaving 1/8″ on either side.
For an outside mount, you first need to determine where the fabric needs to lay on the trim. In some cases you’ll want it to go past the trim and others you’ll want it to come down the middle of the trim.
Measure the full length of trim in three places; top, middle, and bottom.
For this window, the fabric is to overlay a little bit into the trim, but not completely cover it. Looking at how the trim lays, you’ll make this shade 34″, but it will be a fabric-to-fabric measurement.
When the brackets mount, the bracket position won’t matter as much as where the fabric itself will lay down the window. This will be the same for manual or powered shades. With manual shades, you’ll need to determine which side the chain goes on, and with a powered shade you’ll need to determine which side the motor will go on.
Standard or Reverse Roll?
Lastly, you need to decide if the shade needs to be standard roll or reverse roll. Standard roll will go closer to the glass, whereas a reverse roll will fall off the front of the shade. Reversed roll is convenient for instances where you have doorknobs, handles, hardware, etc. on the door, or something that protrudes off the glass itself.