Blinds / Shade Size Calculator
Convert your measured window opening into the correct order size for inside or outside mount, with the standard clearance deduction or overlap already applied. Add a window per opening if you're ordering for more than one.
How this calculator works
Inside mount subtracts a small clearance so the blind can turn and operate without binding on the frame. Outside mount adds overlap so the shade extends past the opening on every relevant side, closing light gaps at the edges:
// Inside mount order_width = measured_width − width_deduction // 0.375 in is common order_height = measured_height − height_deduction // often 0, sometimes ~0.25 in // Outside mount order_width = measured_width + (2 × overlap) order_height = measured_height + overlap // top only is common
Both deduction and overlap values are editable, since they vary by manufacturer — check your specific product's measuring guide before placing a custom order, especially for the height side.
Worked example
A window measured at 36 in wide × 48 in tall:
Inside mount (0.375 in width deduction, 0 in height deduction):
- Order width: 36 − 0.375 = 35.625 in.
- Order height: 48 − 0 = 48 in.
Outside mount (3 in overlap per side):
- Order width: 36 + (2 × 3) = 42 in.
- Order height: 48 + 3 = 51 in.
Same window, two very different order sizes — always double check which mount type your final order is set to before submitting it.
Measuring your window
- Width — measure at the top, middle and bottom of the opening; for inside mount, use the smallest of the three.
- Height — measure at the left, middle and right; same rule for inside mount.
- Depth — for inside mount, confirm the frame has enough clear depth for your chosen blind's hardware, typically at least 2 to 2.5 in.
- Round down, not up — for inside mount, when in doubt, round toward the smaller number so the blind still fits.
Frequently asked questions
Inside mount vs outside mount — what are the pros and cons of each?
Inside mount gives a clean, built-in look but needs enough frame depth — typically at least 2 to 2.5 in — for the hardware. Outside mount doesn't need frame depth, can make a window look larger, and blocks more light around the edges.
Why does outside-mount overlap matter for light gaps?
A shade sized exactly to the opening still leaves light gaps at the edges. Overlap — commonly 2 to 4 in per side — extends the shade past the opening to close those gaps. Too little leaves gaps; too much can look oversized.
What are the tips for measuring a window for blinds?
Measure width at the top, middle and bottom, and height at left, middle and right. For inside mount, use the smallest of each, since the blind needs to fit the narrowest point without binding.
Do blinds come in fully custom sizes?
Yes — most retailers offer made-to-measure sizing to a fraction of an inch. Stock sizes exist too, but only in limited increments, and not every blind type can be trimmed down at home.