How Do You Measure for Blinds? Inside and Outside Recess Fitting Explained
Measuring for new window dressings shouldn’t be a stressful chore. Whether you are updating a classic Victorian terrace in Islington or a sleek Canary Wharf apartment, precise dimensions are the foundation of a perfect fit. At Kelly’s Blinds, we specialize in made to measure solutions that look stunning and function flawlessly. This guide simplifies the technical process for every London homeowner.
Understanding the Basics of Inside vs Outside Recess Fitting
You must first decide whether the blind will sit inside the window frame or be mounted on the wall outside the opening. This choice significantly impacts light control, privacy, and the architectural aesthetic of your room.
| Fitting type | Best for | Key benefit |
| Inside recess | Deep window frames | Provides a neat, integrated look flush with the wall |
| Outside recess | Hiding unattractive frames | Ideal for blocking maximum light by overlapping edges |
Choosing between them often comes down to whether you have protruding handles that might snag the fabric. An inside recess requires sufficient window depth to accommodate the mechanism, while mounting on the wall is more flexible.
Essential Tools for Accurate Measurement
Successful made to measure installation requires professional equipment to avoid common DIY errors. Using the right tools ensures that your dimensions are precise and the final finish is flawless.
- Rigid steel tape measure
- Pencil for marking
- Spirit level
- Sturdy step ladder
A spirit level is particularly important in older London properties where “straight” lines are often an illusion. Check your window lintel and sill before recording anything. We always recommend recording your dimensions in a Width x Height (W x H) format. Swapping these figures is a frequent cause of ordering errors, and because bespoke products are cut to your specific data, they often cannot be returned. Double-check every number before putting the pencil down.
How to Measure for Inside Recess Fitting
To measure for an inside recess, you need to provide the exact “tight” dimensions of the opening without making any deductions. We use these figures to calculate the factory deduction, which is the standard technical adjustment we apply to ensure the blind operates without rubbing against the walls.
- Width: measure the width at the top, middle, and bottom of the recess and use the smallest measurement.
- Height: measure the height at the left, middle, and right and use the largest measurement for most blinds.
- Depth check: ensure your window handles or vents won’t obstruct the blind mechanism.
If your recess is shallower than 50mm, a standard Venetian mechanism might protrude past the wall line. Note that Roman blinds often require the smallest height measurement to prevent the fabric from bunching on the sill.
How to Measure for Outside Recess Fitting
Measuring for an outside recess involves deciding how much of the wall you want the blind to cover. This is the most effective way to achieve a “blackout” effect in bedrooms by minimizing light leakage around the sides of the fabric.
Start by measuring the width of the window opening and adding a supplement to each side. For a professional made to measure look, we suggest adding between 7.5cm and 15cm to the total width. For the height, measure from your desired mounting point—usually at least 7.5cm above the window—down to the sill or floor. If you are fitting blinds in a street-level flat, a larger overlap ensures passers-by cannot see through the gaps at the edges.
Measuring for Specific Blind Types
Every window dressing has a unique mechanical footprint that influences how you should measure. Understanding these technical nuances ensures that the hardware fits perfectly within your specific window configuration.
| Blind type | Key measurement consideration |
| Roller blinds | Fabric is always approximately 3cm narrower than the bracket width |
| Vertical blinds | Width is most critical at the very top where the headrail is fixed |
| Pleated or honeycomb | Require high precision because factory deductions are much slimmer |
| Venetian blinds | Slat depth must clear window handles when tilted |
If you are opting for pleated or honeycomb blinds, you have more flexibility with shallow recesses. For Venetian blinds, the primary concern is whether a 50mm wooden slat will clear your window handle. Checking this now prevents a frustrating installation later.
Common Pitfalls to Avoid When Measuring
Even experienced decorators can fall into traps when preparing for made to measure blinds. Avoiding these common errors will save you time and ensure your bespoke products fit perfectly the first time.
- The single measurement trap where a homeowner assumes the window is perfectly square
- Making self-deductions instead of providing the exact tight opening sizes
- Ignoring protrusions like child safety locks, handles, or decorative tiles
In reality, masonry shifts over time, and a 5mm difference between the top and bottom of a frame can cause a blind to jam. If you subtract “clearance” yourself, and then our workshop applies the standard factory deduction, your blind will arrive too narrow. Always measure twice to ensure you can order once with total confidence.
Transform your room with custom-made blinds. Book a free in-home measurement today.
Unsure which blinds are the perfect fit for your space? Consult a specialist to receive expert advice, tailored recommendations, and personalized solutions that meet your style and functional needs, including roof blinds for unique spaces and more.
FAQ about Measuring for Blinds?
Should I choose an inside or outside recess fit?
It depends on your window’s depth and your light control needs. Inside recess offers a streamlined look for modern London apartments, while outside recess is superior for blocking light and covering uneven window frames.
Do I need to subtract anything from my measurements?
No, please provide the exact opening sizes. We apply the necessary factory deductions to ensure your made to measure blinds fit perfectly with the correct amount of clearance.
Can I use a fabric tape measure?
We strongly advise against this. Fabric tapes are flexible and can stretch, leading to inaccuracies of several millimeters. Only a professional steel tape measure provides the rigidity required for bespoke window dressings.
What if my London bay window is angled?
Bay windows are complex and often require cardboard templates to ensure the blinds don’t clash at the corners. For these structures, we recommend professional assistance to avoid measurement errors.
