How to measure for blinds (and why we do it for you, free)

To measure for a blind, decide first whether it will sit inside the window recess or outside it on the wall, then measure the width and the drop in three places each and use the smallest width and the smallest drop for a recess fit, or add overlap for an outside fit. That is the whole method; the detail below is what stops it going wrong. If you book a free home visit we take every measurement ourselves and the quote is based on ours, so nothing here is required to buy from us.

Recess fit or exact fit?

A recess fit sits inside the window opening, neat and close to the glass, and needs enough depth for the blind to clear the handle. An exact fit (also called outside or face fit) hangs on the wall above the window, covers the whole opening and blocks more light at the edges. Tell the supplier which you want, because the deduction rules differ: for a recess fit the maker takes a small amount off your width so the blind clears the sides; for an exact fit the blind is made to exactly the size you give.

Is the recess deep enough?

Measure from the glass (or the inside face of the handle, whichever sticks out further) to the front edge of the recess. As a rule of thumb, a roller blind on face-fix brackets wants about 70 mm, a top-fixed roller or vertical about 50 mm, and a 25 mm wooden or Venetian slat about 55 mm. Shallower than that, choose an exact fit or a Perfect Fit blind, which clips to the glazing bead and needs no depth at all.

Take three measurements of each

• Width: measure across the recess at the top, the middle and the bottom. Use the smallest for a recess fit.
• Drop: measure from the top of the recess to the sill at the left, the middle and the right. Use the smallest.
• Write the width first, then the drop, in millimetres. Suppliers read "width × drop", and swapping them is the most common ordering mistake.
• Measure the window, not an old blind. Old blinds were deducted already, so copying them makes the new one too small.
• Use a steel tape, not a cloth one, and measure twice.

Roller blinds: the fabric is narrower than the blind

On a roller blind the brackets and the control sit outside the fabric, so the cloth is about 30 to 35 mm narrower than the overall width you order. For a recess fit that is fine. For an exact fit on the wall, add at least 70 mm to the window width so the fabric still covers the glass, and 100 mm or more to the drop so the roll sits above the opening.

Bay windows

A bay is measured as separate windows, one blind per face. Measure the width of each face at the point where the blinds will hang, and remember that at the corners two blinds must not clash, so recess-fit blinds in a bay are usually ordered a little narrower on the inner faces. Square bays and angled bays are measured the same way; a curved bow window needs one blind per pane of glass. This is the window type where most self-measured orders go wrong, and the one we would always rather measure for you.

uPVC windows, tilt-and-turn and doors

Drilling into a uPVC frame is best avoided: the frame may be warranted and the screw can hit the reinforcing or the glazing unit. Perfect Fit and INTU blinds clip into the glazing bead with no screws and no drilling, and they move with a tilt-and-turn window or a door. For those you measure the visible glass height and width and tell the supplier the bead depth; we carry the gauges for every common profile.

Velux and roof windows

Do not measure a roof window at all: read the code on the data plate on the top of the open sash, for example GGL MK04. Skylight blinds are made to that code and fit the frame exactly.

Measure before or after tiling?

After. Tiles, a new sill or a window board change the recess by their own thickness, and a blind made to the old size will not fit. If you are decorating, book the visit for when the window is finished.

Let us measure instead →on a free home visit, with the sample books, and a fixed quote on the day.

Facts checked 3 November 2026. Prices and lead times are those published on this site at that date; the quote you receive on your visit is the one that counts.