How to Measure Window Openings: Step-by-Step Guide

Tools You Will Need

• Tape measure — at least 10 feet long for measuring both the window and your furniture.
• Pencil and paper (or your phone) to record measurements.
• Step stool — most windows are at waist height or higher, and you need to measure the full opening.
• Screwdriver (Phillips and flat-head) — needed if you plan to remove the sash or screen.

Step 1 — Identify Your Window Type

Before measuring, identify what type of window you have. Double-hung windows (two sliding sashes) are the most common in US homes. Casement windows have a crank and swing outward. Sliding windows move horizontally. The type determines how the window opens and what your usable opening will be. If you are not sure, look for a crank handle (casement), sash locks at the top of the bottom sash (double-hung), or a horizontal track (sliding).

Step 2 — Measure With the Window Fully Open

• Open the window as far as it will go in its normal operating mode.
• For double-hung: raise the bottom sash to its highest point. The opening is the space between the sill and the bottom of the raised sash.
• For casement: crank the sash fully open. The opening is the full frame minus the hinge hardware.
• For sliding: slide the operable panel fully to one side. The opening is the half of the frame that is now clear.
• Measure the width at the narrowest point (top, middle, and bottom of the opening — use the smallest).
• Measure the height at the narrowest point (left side, center, and right side — use the smallest).

Step 3 — Measure With the Sash Removed (If Applicable)

If the opening with the sash in place is too small, measure what you would get with the sash removed. On a double-hung window, removing the sash converts the half-height opening into the full frame opening — typically doubling the usable height. Measure the full frame opening from the sill to the head jamb (top of the frame), and from jamb to jamb (left to right), subtracting the track width on each side (0.5 to 1 inch per side). This is your maximum possible opening.

Step 4 — Account for Screens, Locks, and Limiters

• Window screens: Must be removed before moving furniture. Most screens pop out from the inside by pressing spring-loaded tabs.
• Window locks and latches: On double-hung windows, the sash lock is at the top of the bottom sash. It does not reduce the opening but must be unlatched to open the window.
• Opening limiters (child safety devices): Many windows have stops that prevent the window from opening more than 4 inches. These must be disengaged or removed for full opening. Look for a button, clip, or set screw on the track.
• Storm windows: Exterior storm windows must be raised or removed for full access. On older homes, storm windows may be screwed into the frame.
• Muntins (grid bars): If the window has decorative grids between the panes, check whether they are real (structural) or snap-in (removable). Snap-in grids pop out and do not reduce the opening.

Step 5 — Measure the Sill Height and Exterior Clearance

• Sill height: Measure from the floor to the top of the window sill (the interior ledge). This determines the loading angle — low sills (under 30 inches) are easier for passing furniture through.
• Exterior clearance: Look outside. Is there a clear path below the window for hoisting? Are there bushes, fences, AC units, or fire escapes blocking access?
• Floor height: Which floor is the window on? Ground floor windows can be accessed from outside without hoisting equipment. Second floor and above require rigging.
• Overhang or awning: Check for exterior overhangs, awnings, or balconies above the window that may interfere with hoisting.

Common Measurement Mistakes

• Measuring the full frame size instead of the opening — the usable opening is always smaller due to tracks, stops, and hardware.
• Forgetting that double-hung windows only open to half their height — measure the actual opening, not the full window.
• Not removing the screen before measuring — the screen frame reduces the opening by 0.5 to 1 inch on each side.
• Ignoring opening limiters — child safety stops restrict the opening to 4 inches unless disengaged.
• Measuring inside with the sash up but not checking exterior clearance — obstructions outside can prevent furniture from passing through even if the opening is large enough.