Blind and shade size calculator

How it works

Measure the opening with a steel tape in three places each way, to the nearest 1/8 inch. Windows are rarely square, and the three numbers tell you how far out they are.

inside mount:  order width  = narrowest width, rounded down to 1/8 in
               order height = longest height, rounded down to 1/8 in
               finished blind = order width - factory deduction
outside mount: order width  = widest width + 2 x overlap
               order height = longest height + extra above + extra below

Inside mount. Give the maker the exact opening and let the factory take its own deduction off the width, so the headrail and brackets clear the frame. If you take it off yourself as well, the blind comes out too narrow and leaves a wide gap at each side. Deductions run from about 1/8 to 1/2 inch depending on the product, and the maker's measuring guide gives the exact figure. Use the narrowest width so the blind fits at the tightest point, and the longest height so it reaches the sill all the way across. If the widths differ by more than 1/4 inch, an outside mount hides the gaps better.

Outside mount. The blind is made at exactly the size you order. An overlap of 1-1/2 to 3 inches each side cuts the light that leaks round the edges. Add 2 to 3 inches above the opening for the headrail and brackets, and the same below if there is no sill for the blind to rest on.

An inside mount also needs enough depth in the frame for the headrail. Check the product's minimum mounting depth against the window before you order.

Typical overlaps for an outside mount