Overview
Choose the intended inside-frame position and check its usable depth before measuring width and drop. Include moving hardware in the check. Then use the matching square-set, architrave or sill method below.
Measuring for an Inside Mount
Confirm the frame and obstruction clearances first. Then record three widths and three drops using a metal tape. Keep all six readings, choose the smallest width and drop, and leave manufacturing deductions to us. Do not assume a rectangular-looking opening is square.
Find the front reference point
Use the room-side front edge of the recess as the reference plane. Measure inward from that same plane at every checking position; changing the starting surface gives inconsistent clearance figures.
Examples of obstructions
Look for window winders, locks, security fittings, handles, keys, screens and opening sashes. Include anything that projects into the area where the frame, rails or blades will sit.
Measure to the first obstruction
Stop the depth measurement at the first obstruction the shutter could touch. This gives the clear space available. A deeper measurement to the glass is not usable if a handle or screen occupies part of it.
Check several locations
Check top, middle and bottom on both sides. Record the smallest clear depth and the location of each obstruction. A recess may taper or contain hardware at only one height.
Operate the window
Open the window and operate its handles or winders while checking the proposed shutter position. Moving hardware must stay clear too. If available depth is below 70 mm or fittings enter the recess, use the frame-specific obstruction checks before committing to an inside mount.
Measuring Inside Mount for a Square-Set Window
Within the opening, take widths at the top, middle and bottom. Take drops at the left, centre and right. Record the smallest width and the smallest drop without subtracting a fitting allowance.
Measuring Inside Mount for a Window with an Architrave
Measure inside the recess, not across the architrave. Check three widths and three drops and use the smallest of each. The trim remains outside the measuring boundary for a recess fit.
Measuring Inside Mount for a Square-Set Window with a Sill
Take three drops from the sill's upper surface to the inside top of the opening. Take three widths within the recess. Use the smallest width and smallest drop, with no manufacturing deduction of your own.
Measuring Inside Mount for a Window with a Sill and Architrave
Keep width measurements inside the recess even though trim surrounds it. Measure three drops from the top of the sill to the inside top and three widths across the opening. Record the smallest of each and specify the projecting sill in the order.
