How to Measure for Curtains and Blinds

Fit the pole or track first

Nothing can be measured until you know where the curtains will hang from, because every width and drop figure is taken from the pole or track, not from the window. Put the pole up first, or at the very least decide exactly where it goes and mark it on the wall.

• A pole is the visible option: a round rod on brackets with decorative finials at the ends, used with rings or with eyelet curtains threaded straight onto it. It suits most rooms, and it is the easier of the two to fit.
• A track is a slim channel that the curtains glide along, usually painted out or hidden behind a pelmet or the curtain heading. It is the better choice for bay windows and curved runs, for very heavy curtains, and wherever you want the curtains to draw back as far as possible.
• Height above the window. Fitting the pole 15 to 20 cm above the window frame is the usual advice: it makes the window look taller and lets more light in when the curtains are open. Where there is space, higher still looks better.
• Width beyond the window. Extend the pole 15 to 20 cm past each side of the frame so the open curtains sit against the wall rather than over the glass. This is the single easiest way to make a room feel brighter.

Width: measure the pole, then add fullness

Measure the length of the pole between the finials, or the full length of the track. That figure, not the window width, is what everything else is based on. If you are using a pole, ignore the finials themselves, since curtains do not travel over them.

Curtains need to be considerably wider than the pole, or they hang flat and thin instead of falling in folds. As a working rule, you want a total curtain width of roughly 1.5 to 2 times the pole width, taking both curtains together. Around 1.5 times is enough for lightweight or voile panels; closer to 2 times gives the fuller, more generous look most people are picturing, and heavier and pleated headings want more rather than less.

One exception worth knowing: a single curtain hung to one side, which suits a narrow window or a door, still needs the same total fullness on its own, so it has to be a much wider panel than half a pair.

Drop: where should the bottom land?

The drop is a style decision first and a measurement second. There are three conventional places for curtains to finish, and they suit different windows.

• To the sill. The bottom finishes just above the sill, usually by a centimetre or so, so the curtains hang free. Practical for kitchens, bathrooms and any window with a radiator directly beneath it, and the least fabric to buy.
• Below the sill. Finishing roughly 15 cm below the sill covers the wall under the window and looks less abrupt than a sill-length curtain. A good middle option for bedrooms.
• To the floor. The most formal and the one that makes a room look taller. Aim to finish about 1 cm clear of the floor so the curtains do not drag or collect dust. Some people deliberately add a few extra centimetres so the fabric pools slightly on the floor, which looks lovely and is a nuisance to vacuum around.

Where to start measuring from

This depends entirely on the heading, and it is the other place ready-made curtains go wrong.

• Eyelet curtains thread straight onto the pole, so measure from the top of the pole down to where you want the curtain to finish. The fabric sits a little above the pole, which is normal and is already allowed for in the stated drop.
• Pencil pleat, pinch pleat and tab-top curtains hang from rings or hooks, so measure from the bottom of the ring (the small eye the hook clips into) down to the finish point. On a track, measure from the top of the track.
• Pencil pleat curtains have some adjustment built in, because the hooks can go into different rows of pockets in the heading tape, which shifts the hanging height by a few centimetres either way. That flexibility is useful when your window sits between two ready-made drops.

UK ready-made sizes, and what to do in between

Ready-made curtains in the UK come in a small set of standard sizes, inherited from imperial measurements, which is why the numbers look arbitrary. Widths are quoted per curtain:

• Widths: 117 cm, 168 cm and 228 cm per curtain (46, 66 and 90 inches). A few ranges go wider.
• Drops: 137 cm, 183 cm and 229 cm (54, 72 and 90 inches). Some ranges add a shorter drop for sill-length windows and a longer one for tall rooms.

Very few windows land exactly on those numbers, so most of the skill in buying ready-made is knowing which way to round.

• Width: always round up. Extra width becomes extra fullness, which looks better, not worse. Rounding down is what produces a thin, stretched pair that will not close properly.
• Drop: it depends which way you are stuck. Too long can be taken up, either by a seamstress or, on pencil pleat curtains, partly by moving the hooks to a different row of the tape. Too short cannot be fixed. Given the choice, buy the longer drop.
• Between drops with nowhere to go? Move the pole. Raising or lowering the pole a few centimetres is free and often turns an awkward in-between window into a straightforward one, and a higher pole usually improves the room anyway.
• When nothing fits, made-to-measure exists. If the window is unusually wide, unusually tall, or in a bay, made-to-measure costs more but removes the compromise entirely.

Blinds: inside or outside the recess

Blinds work to a different rule, because the first decision is whether the blind sits inside the window recess or on the wall in front of it. Decide that before measuring anything, and write "recess" or "exact" on your notes, because those are the words suppliers use.

Inside the recess

The blind sits within the window opening, giving a neat, flush look that leaves the sill clear. Measure the width of the recess at the top, the middle and the bottom, and use the smallest of the three, then measure the height on both sides and in the middle.

The important part: when you order a made-to-measure blind as a recess fit, the supplier takes the deduction, not you. They subtract a small amount, typically around a centimetre, so the blind clears the sides and can actually move. Deducting it yourself as well is a common and expensive mistake, and it produces a blind with a visible gap down each side. Give them the true recess measurement and say it is a recess fit. Be aware that a recess-fitted blind never blocks light completely, because that clearance gap is always there.

Outside the recess

The blind is fitted to the wall or the frame above the window and overlaps the opening. It blocks noticeably more light, makes a small window look larger, and is the answer for a shallow recess that will not take the blind mechanism. Measure the width you want the blind to cover, allowing an overlap of around 5 to 10 cm on each side, and decide how far above the window the top will sit. Here the measurement you give is the finished size you want, so check that the supplier is not deducting anything.

• Roller blinds are the slimmest and cheapest, and the most likely to fit a shallow recess.
• Roman blinds are fabric and fold into soft pleats, so they sit closer to curtains in feel and need more depth.
• Venetian blinds tilt, which lets you keep daylight while losing the view in, and suit kitchens and bathrooms.

Lined, thermal or blackout

These three terms overlap and get used loosely, which makes them harder to compare than they should be. Here is what each one is actually doing.

• Lined simply means a second layer of fabric behind the main one. It makes the curtain hang better, protects the face fabric from sunlight and adds a little insulation and light blocking. Unlined curtains are lighter and let more light through, which is the point of a voile.
• Thermal curtains have a lining designed to slow heat moving through the window: they keep warmth in during winter and help keep rooms cooler in summer. The effect is real but modest, and depends on the curtains covering the window generously and being closed at the right times.
• Blackout describes the light-blocking layer, usually a dense coated lining. It is the one to look for in a bedroom, a nursery or a room that faces a street light. Note that even a genuine blackout curtain will let light in around the edges unless the pole extends well past the window and the curtains are generous in width.

The labels are not exclusive: many blackout curtains are also sold as thermal, because a dense lining does both jobs. If the aim is a dark bedroom, combine a blackout blind fitted outside the recess with curtains over the top, which handles the edge gaps that neither can fix alone. Voile curtains do the opposite job, softening daylight and adding daytime privacy, and are often hung on a second pole behind the main curtains.

The mistakes that come up again and again

• Measuring the window instead of the pole. The window decides where the pole goes; the pole decides the curtain size.
• Forgetting that ready-made widths are per curtain. A 168 cm pair is 336 cm of fabric, not 168 cm.
• Buying exactly the pole width. Curtains that match the pole have no fullness, look mean and will not close properly.
• Hanging the pole tight to the frame. Extending 15 to 20 cm past each side lets the curtains stack against the wall instead of over the glass.
• Deducting the recess clearance yourself. For a made-to-measure recess blind, give the true recess size and let the supplier make the deduction.
• Measuring the drop in one spot. Take it in three places; floors and windows are rarely true.
• Using a fabric tape measure. It stretches. Use a steel tape, and get a second person for anything above shoulder height.
• Ignoring the radiator. Floor-length curtains in front of a radiator send a good deal of the heat up the window rather than into the room; sill-length is the practical choice there.

Once you have your numbers, the rest is choosing. Browse all curtains and blinds, or go straight to eyelet curtains, pencil pleat curtains or curtain poles and accessories. We track live prices across the UK retailers we list, so you can compare the same size and heading across several before you buy.