Replacing my window blinds- proper way to measure window?

depends on if you want a outside or inside mount

If the blinds are to fit inside your window:

1. Measure your window in 3 places horizontally: top, middle, bottom
2. Measure in two places vertically: about 3 inches in from side of casement
3. Use the narrowest horizontal and
4. the longest vertical for your window measurements. Blinds are typically cut slightly narrower than the horizontal measurement you have given, so:

If you are confident that your measurement is spot on and you want the blind to be the exact horizontal measurement you have given, you can request the blinds be cut as an outside mount (meaning it does not fit into the casement but is attached to the wall like a curtain) but order inside mounting brackets. If you do not specify the inside mounting brackets the company will send outside mounts.

If the blinds are to be outside your window:

1. Measure as above, but take the widest measurement for the horizontal, and
2. longest for vertical

Both can be slightly wider and longer, if you wish.

Inside-Mounted Horizontal Blinds

1. Measure exact window width at top, middle, and bottom.
2. Use the narrowest width. Do not make any deductions - provide the exact measurements of the narrowest width. ...
3. Measure exact window height at left, middle, and right side.
4. Use longest height.