The short answer
Identify the exact pole, track or blind and whether it will sit inside or outside the recess. Take preliminary measurements using that supplier's instructions, without adding your own deductions. Consider handles, opening windows, radiators and the finished curtain drop, and keep all brackets and safety devices with the product.
A useful measurement tells us what was measured as well as the number. Window-opening width, pole length, blind mechanism width and fabric width are different dimensions. Keeping those separate helps avoid ordering a fitting that cannot achieve the intended result.
How do I measure for a curtain pole?
Start with the window opening and the usable space around it. A pole usually needs room for the fabric to gather at the sides, while finials add to the overall span. The required position also depends on the curtain heading, desired drop, ceiling or coving and bracket projection.
Keep the opening width, usable pole length and overall length including finials separate in your notes. There is no universal drilling height or side allowance that suits every window. John Lewis's curtain buying guide illustrates how the measurement reference changes with the heading type.
For a planning reference, John Lewis suggests placing a pole 10-15 cm above the opening and extending it 15-20 cm each side. Those are that retailer's guide figures, not compulsory drilling offsets. Restricted side walls, thick curtains, coving or an existing curtain drop can require a different layout. Allow for the opened fabric as well as the finials so the curtains can uncover the glass.
The usable track or pole span, excluding finials, is the starting measurement for choosing curtain width. It is not automatically the finished width of one fabric panel: the heading, required fullness and supplier's single-panel or pair convention determine the fabric quantity. The drop reference also changes with the heading: John Lewis measures pencil pleats from the ring eye and eyelets from the top of the pole. Record that reference point so the intended hem position is clear.
If the curtains are already bought, share their size and heading as well as the pole. Choosing the pole position without considering the finished fabric can leave a curtain too short or dragging on the floor.
What is the difference between recess and exact blind measurements?
A recess measurement describes the opening the blind must fit within, while an exact measurement normally specifies the blind size being ordered. The supplier's definition still controls: some dimensions include the mechanism or brackets, and the fabric can be narrower than that overall width.
Name the width before you order
Inside the recess
A: The recess is the opening. Follow the supplier's measuring positions and order option, including who makes the fitting deduction.
Outside the recess
B: Overall blind width and C: fabric width are different on many roller blinds. Check what the supplier means by an exact-size order.
Illustrative roller blind. Recess deductions, overall widths and fabric allowances vary by product and supplier.
Do not make an extra deduction unless the product's current ordering instructions tell you to. Guides can vary by blind type: the narrowest recess measurement is not a universal rule for every roller mechanism. The Blinds2Go roller guide is one example of product-specific measuring and allowance instructions.
For an outside-recess blind, the intended overlap, fabric coverage and mounting position need planning together. Blackout fabric does not by itself eliminate gaps around the edges of the installed blind.
For example, Blinds Direct states that its roller cloth is approximately 3-4 cm narrower than the ordered overall width. An illustrative 120 cm exact order under that convention could therefore have roughly 116-117 cm of cloth. The same supplier requests top-width measurements for specified roller products, while its general recess instructions use the smallest measurement. These examples show why 'recess' alone is not a complete measuring method. Blinds Direct's measuring guide sets out the distinctions.
- Record the supplier, blind range and any cassette or no-drill upgrade.
- Record whether the order field asks for recess size, mechanism width or fabric width, plus the measurement units.
- Note width changes caused by tiles or an uneven opening, the available depth and protruding handles.
- Keep a copy of the measurements and selected order option. Do not transfer deductions from a different blind type.
What could stop the curtain or blind fitting properly?
The product must fit both the opening and the space it moves through. Before ordering, compare the proposed bracket position with open windows, projecting handles and the gathered fabric. A blind that fits the recess when everything is closed may obstruct the handle or stop an inward-opening sash from moving.
- Window handles or inward-opening windows in the blind's path.
- A radiator, sill, furniture or deep curtain heading needing extra projection.
- Coving, a sloping ceiling or limited wall space beside the opening.
- Tiles, an unknown lintel or an uncertain fixing surface.
- Brackets, connectors or safety devices missing from the supplied kit.
For a hypothetical bedroom, the blind's quoted width fits the opening but its fabric would pass in front of a projecting handle. The next decision is the mounting position and available recess depth, not an extra width deduction. If moving the blind forward still cannot give clearance, compare an outside-recess product before placing the order. Reusing old bracket positions is also a separate suitability check, especially where holes are loose or damaged.
If a fitting is already loose, catching or uneven, our curtain and blind fitting problems article explains the difference between a mounting fault, a clearance problem and a product mechanism that needs supplier support.
Do blind cords and chains need safety fittings?
The blind's required cord or chain safety arrangement is part of the installation. Depending on the system, it may use a tensioning device, cleat or a design without accessible looped cords. The supplied instructions determine what needs fitting and how the blind should be used.
Keep the safety devices with the blind and allow access to the intended fixing position. The BBSA Make it Safe guidance explains the risk from accessible cords and the importance of the correct safety arrangements. A device left in the packet does not complete the installation.
What should I send before arranging installation?
Send the number of windows, photographs, product links and approximate dimensions. Tell us whether the products are already ordered and whether old fittings need taking down. Bay windows, high-level windows and heavy curtains can affect access, equipment and the fitting arrangement.
Clear the window area before the agreed visit and keep the complete kit available. If measurements or product suitability are uncertain, discuss that before ordering custom sizes. Our curtain and blind fitting service can be scoped around the actual windows and chosen products.
What should accompany a local window-fitting enquiry?
The East Sheen and East Molesey pages consider how the product will operate in the room, including fixing positions and surrounding obstructions. Send the full address and whole-window photos with the measurements, so the visit can be planned around access as well as the new fitting.
For replacing a pole or blind in Cheam or Chiswick, include a view of the old installation. Their local planning notes distinguish removing and fitting from filling old holes or restoring a paint finish. State which of those results you want included before a quote is agreed.
The Worcester Park notes cover agreeing the position and permission before ordering. Confirm any restrictions on drilling and identify the exact street for the parking arrangements; a shared postal area does not settle which council information or permit applies to the address.
Common questions
Sources and further reading
Product instructions apply to the particular fitting or finish. These references explain the general distinctions used here.
Have the windows in mind?
Send the number of windows, product links and any photographs you have. We can discuss the fitting before you commit to uncertain measurements. If you are in Teddington or Cobham, include your postcode and which rooms need fitting.
Ask about fitting