Blind Size CalculatorWhat Size Blinds Do I Need?

What size blinds do I need?

It depends on where the blind will sit. Inside the recess, the blind needs to be a touch narrower than the gap so it opens and closes without catching. Outside the recess, it needs to be wider and longer than the window so light can't creep round the edges.

Most ready-made blinds come in set widths and can be trimmed down to fit. So the rule is simple. Buy the nearest size that's at least as wide as you need, then trim it. You can take width off a blind. You can't add it.

Inside or outside the recess?

An inside fit looks neat and leaves the wall around the window clear. It works best when the recess is deep enough for the brackets and nothing sticks out, such as handles or a window that opens inwards.

An outside fit covers the whole frame and a strip of wall around it. It blocks more light at the edges, which matters in bedrooms, and it's the answer when the recess is shallow or the handles get in the way.

How to measure for blinds

1. Use a metal tape measure. Fabric tapes stretch.
2. For an inside fit, measure the recess width at the top, middle and bottom. Use the narrowest figure, because recesses are rarely square.
3. Measure the recess height on the left, in the middle and on the right. Use the shortest figure.
4. For an outside fit, measure the width and height of the area you want to cover, then allow at least 10cm extra on every side so no light gets through.
5. Check for anything in the way, such as window handles, trickle vents or a radiator below the sill, before you fix the brackets.

Standard blind sizes

Ready-made blinds come in widths from 45cm to 180cm. Widths include the brackets, so the fabric or slats are a few centimetres narrower than the size listed. Roller blinds come with a 165cm drop and venetian blinds with a 160cm drop. Not every style comes in every width, so the width pages show what's available.

Can I cut a blind to size?

Yes. Roller blinds can be trimmed in width, and the instructions in the box show you how. Trim both ends evenly so the blind sits centrally. The spare drop simply stays rolled on the tube.

Venetian blinds can be shortened by removing slats. PVC venetians can only lose about 2cm from each side, so choose a width close to your measurement. If your recess falls between two venetian sizes, an outside fit or a roller blind is usually the easier option.

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