Home & Electrical

Blind Size Calculator: Measure for Inside or Outside Mount Window Blinds

Free tool · Updated October 3, 2026 · By CouponTalk

Your result

Enter your measurements to see your result.

Quick answer

For an inside-mount blind, measure the recess at the top, middle and bottom and use the smallest width; most makers then deduct about 1 cm so the blind runs freely. For an outside mount, add about 7.5–10 cm on each side and 7.5–10 cm above and below to block light. A 120 × 150 cm window needs about a 140 × 170 cm outside-mount blind.

How to use this calculator

Measure the window width at three heights and the height at three points.
Choose inside or outside mount.
For outside mount, choose the overlap.

Inside vs outside mount

Inside vs outside mount
Mount	Width	Height	Best for
Inside the recess	Recess width (maker deducts about 1 cm)	Recess height	Neat look, deep recesses
Outside on the wall	Window + 7.5–10 cm each side	Window + 7.5–10 cm top and bottom	Blocking light, shallow recesses

Follow the seller's measuring guide when ordering.

Frequently asked questions

Inside or outside mount?

Inside looks neat if the recess is deep enough (about 5 cm for rollers). Outside blocks more light and suits shallow recesses.

Should I deduct for inside mount myself?

Check the seller's guide: many ask for exact recess size and deduct themselves.

How much overlap for a dark room?

Add 10 cm each side and above for bedrooms and home theatres.

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