> Editorial Note: I’m Erin Schwartz, and I cover home decor with a bias toward what actually works in a real room. The guidance here weighs scale, layout, and materials against Apartment Therapy and Wirecutter coverage rather than styling a space that nobody lives in.
The shade arrives an inch too narrow, and nine times out of ten it’s because someone measured once instead of three times. Windows are rarely perfectly square, so a single measurement hides the taper that leaves a gap. These related guides help you finish the job: window curtain rods, bay window curtains, small window curtains, how to measure a tv, how to clean window tracks, and how to clean window blinds.
Decide Inside Mount or Outside Mount First
Choose inside or outside mount before you touch the tape, because the two need different measurements and can’t be swapped later. An inside mount sits the shade inside the window frame for a clean, built-in look, and it needs at least 2 to 3 inches of flat depth at the top of the frame to hold the brackets. Measure that depth first: too shallow, and the shade protrudes or won’t fit at all.
An outside mount fixes the shade to the wall or trim above the window. It’s the fix for shallow frames, out-of-square openings, or when you want maximum light blockage, since the shade overlaps the frame edges. Outside mounts also make a small window look larger because the shade extends beyond the glass.
The choice drives everything after it. Get it wrong and every number you write down is measuring the wrong thing. As a rule, reach-in frames on older homes run shallow, so check the depth before you assume an inside mount is even possible.
Measure Width in Three Places
Measure the width at the top, middle, and bottom of the window, because openings drift out of square as houses settle. For an inside mount, record every reading and use the narrowest of them, so the shade clears the tightest point. A shade cut to the widest measurement will bind or refuse to seat. A difference of even 1/4 inch across those three points is common in framing more than a decade old.
Use a steel tape, not a fabric one, for the frame width. A cloth tape sags across a 36-inch opening and reads long, which is exactly the error that makes an inside-mount shade too wide. Round down to the nearest 1/8 inch on inside mounts and let the manufacturer take their standard deduction.
For an outside mount, add 3 to 4 inches to the total width, splitting it so the shade overlaps 1.5 to 2 inches on each side. That overlap is what blocks the light gap along the edges.
Measure Height and Account for Overlap
Measure the height in three spots too: left, center, and right of the opening. For an inside mount, use the longest of the three so the shade fully covers the glass, then let the factory deduction set the exact drop. Openings that lean will otherwise leave a triangle of bare window at the bottom.
For an outside mount, measure from where you’ll place the bracket, usually 3 inches above the frame, down to the sill or 3 inches below it. Adding that top clearance hides the roller or headrail and stops light from spilling over the top edge. Wirecutter notes that this top overlap is the detail most people skip, and it’s why store-bought shades often glow at the top.
Write width first, then height, always. The industry standard lists width by height, and reversing them ships a shade rotated 90 degrees. Note the measurement in ink on a diagram of the window, not from memory, so a second window’s numbers don’t blur into the first.
What You’ll Need
A reliable tape is the whole job here, so these picks are ranked by owner rating and split between rigid steel tapes for frame width and soft tapes for curves. Reach for a steel tape for the actual window opening, since it holds a straight line across the span. The soft tapes below suit rounded or specialty windows.
The SENDA 10-foot compact tape leads at a 5.0 rating with metric and inch markings. The NBTOOL 120-inch soft tape with a suction cup sits at 4.7, and the Yoolax tape is purpose-labeled for motorized blinds and shades at 4.6. The Zabiki 25-foot steel tape with a magnetic tip also holds 4.6, the one to grab for a rigid frame reading, and the Oiyaku 60-inch soft tape rounds out the set at 4.5.
Frequently Asked Questions
Do I measure the window or the frame for shades?
It depends on the mount. Inside mounts measure the inside of the window frame opening. Outside mounts measure the area you want the shade to cover, adding 3 to 4 inches of overlap.
Why do I measure the width in three places?
Because windows go out of square as a house settles. The top, middle, and bottom often differ by a quarter inch or more. For inside mounts you use the narrowest so the shade clears every point.
Should I round up or down when measuring for shades?
Round down to the nearest 1/8 inch for inside mounts, so the shade fits inside the tightest spot. For outside mounts, round up, since a little extra coverage only helps block light.
How much depth does an inside mount shade need?
At least 2 to 3 inches of flat frame depth at the top to hold the brackets. Shallow frames can’t take a full inside mount, so an outside mount becomes the practical choice.
Do I list width or height first?
Width first, always. The industry standard is width by height, so reversing the two ships a shade turned 90 degrees. Double-check the order before you submit the numbers.
What tape measure should I use for windows?
A steel tape for the frame width and height, since cloth tapes sag and read long over a 36-inch span. A soft tape helps only for curved or arched specialty windows.
How much overlap should an outside mount have?
About 1.5 to 2 inches on each side and 3 inches above the frame. That overlap covers the light gap along the edges and hides the headrail at the top.
Bottom Line
Measuring for shades comes down to one decision and one habit: pick inside or outside mount first, then measure width and height in three spots each and record width before height. Inside mounts use the narrowest width and need 2 to 3 inches of frame depth; outside mounts add 3 to 4 inches of overlap to kill the light gap. If your frame is shallower than 2 inches or clearly out of square, go outside mount rather than forcing a shade that won’t seat.
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