3 minutes with a steel tape measure. No tradesman needed — thousands of DIY installs get it right first time by following these three rules.
Inside mount — shutters sit neatly inside the window reveal. Measure the inside of the frame. Choose this if your reveal is at least 35 mm deep and square.
Outside mount — shutters fix to the wall over the frame. Measure the outside of the window frame itself, adding 30–50 mm on each side so the shutters cover the frame and let in maximum light.
Width: measure at the top, middle and bottom of the opening. Height: measure at the left, middle and right. Old frames are rarely square — use the smallest number for each. Enter millimetres (e.g. 1235 mm).
Each panel should be roughly 450–900 mm wide. The order form suggests a panel count automatically from your width — 3 and 4-panel windows carry a small hardware surcharge (+$30 / +$50 per window).