Blind Size Calculator

How Do You Measure a Window for Blinds?

Measure the window width in three places: top, middle, and bottom of the recess. Use the smallest of the three numbers, since windows are rarely square. Measure the height on the left, centre, and right of the recess, and use the longest number. Check the recess depth at each corner. Anything under 6 cm of depth rules out some inside mount blind types. Write the measurements down in centimetres or inches, depending on the units your supplier uses.

What Is the Difference Between Inside and Outside Mount?

An inside mount blind sits within the window recess. The brackets attach to the reveal (the inside walls of the recess). The blind covers only the glass. Inside mounts look clean and built-in. An outside mount blind fixes to the wall or window frame in front of the opening. It overlaps the edges by 5 to 10 cm on each side so no light leaks around the blind. Outside mounts work when the recess is too shallow or when you want maximum coverage.

How Much Overlap Do You Need for an Outside Mount?

Ten centimetres on each side and 10 cm across the top is the standard overlap. That covers most trim and reveals. Add another 5 cm at the bottom for the sill. For a window 120 cm wide by 140 cm tall, the outside mount order is 140 cm wide by 155 cm tall. Rooms with deep decorative architraves may need more overlap so the blind clears the moulding.

How Deep Does a Window Recess Need to Be for Inside Mount Blinds?

At least 6 cm for most roller and pleated blinds. Roman blinds need 8 cm because the fabric folds thicker. Venetian blinds need 5 cm for the headrail plus 2 cm for the slats to tilt. Vertical blinds need only 4 cm because the track is thin. If the recess is shallower than the blind requires, the blind will protrude past the wall and look unbalanced. In that case, outside mount is the better choice.

What Is a Pattern Repeat and Why Does It Matter?

A pattern repeat is the vertical distance before a fabric pattern repeats itself. If the pattern is 15 cm tall before the same motif appears again, the repeat is 15 cm. Roman and pleated blinds made from patterned fabric need the finished height rounded up to the next full repeat. That way the pattern sits complete at both the top and bottom of the blind. Skipping this step cuts the pattern mid-motif and leaves an odd strip at one end.

Which Side Should the Control Be On?

Put the control on the side away from the nearest wall. If the window sits in a corner, a right-side chain is easier to reach than a left-side chain pressed against the wall. For large windows over 180 cm, dual controls (both sides) reduce the effort and stop the fabric from skewing. Motorised blinds remove the question entirely and work well for high or hard-to-reach windows.

What Cord Loop Length Should You Choose?

Short loops reach two-thirds of the blind height. Standard loops match the full height. Long loops reach the floor. Short loops suit tall windows where you don’t want dangling cord. Long loops make the blind easier to operate but need a cleat or tensioner to keep the cord out of reach. Cordless and motorised options skip the loop entirely, which is the safest choice around young children.

What Are the Blind Safety Standards?

Three main standards apply. EN 13120 covers the EU and UK. It requires corded blinds to have a safety device or be manufactured cordless. ANSI/WCMA 2022 is the US standard and increasingly favours cordless designs for any window a child could reach. AS 6001 is the Australian standard and specifies cord lengths, tensioners, and warning labels. Whichever standard applies, if children use the room, choose cordless or tensioned blinds.

How Do You Fit a Blind Without a Drill?

Some rental-friendly options exist. Tension-fit blinds sit in the recess without screws. No-drill brackets use strong adhesive pads rated for light blinds. Velcro and hook-and-loop systems work for lightweight pleated blinds. None of these match a screwed bracket for security on heavy blinds. For blackout roller or roman blinds, you’ll need a drill and proper fixings. The tolerance field in the calculator covers the small clearance the blind needs if you’re fitting into a tight recess.

Common Mistakes When Ordering Blinds

Measured once instead of three times. Windows are rarely perfectly square, and the smallest measurement is the one that matters. Forgotten depth. Recess depth determines whether inside mount is viable at all. Wrong units. Ordering in inches when the measurements were taken in centimetres is an expensive mistake. Ignored pattern repeat. Skipping the repeat calculation produces a blind that looks trimmed. And cord safety. Old corded blinds are the leading cause of strangulation incidents in UK homes for children under five. Buy cordless or fit a tensioner.