Measure the window opening in three places and use the smallest figure for a recess fit, or add 70–100 mm of overlap each side for a face fit. Measure in millimetres, never centimetres, and never deduct anything yourself — the manufacturer makes the deduction.
An installer measures the same way, on site: see blind installation in Cape Town.
Recess Fit or Face Fit
Every blind is made to one of two mounting decisions, and the measurement changes completely between them.
| Recess (inside) fit | Face (outside) fit | |
|---|---|---|
| Where it sits | Inside the window reveal | On the wall or frame above the opening |
| Width measured | Narrowest of three points | Opening + 70–100 mm each side |
| Drop measured | Reveal top to sill | Above opening to 50 mm below sill |
| Minimum reveal depth | 55 mm roller, 70 mm venetian | None |
| Light gap | 3–5 mm each side | Effectively none |
| Best for | Neat look, deep reveals | Blockout, shallow reveals, out-of-square openings |
How to Measure for Blinds: The Three-Point Rule
Openings are rarely square. Measure the width at the top, the middle and the bottom of the reveal, then the drop at the left, centre and right. For a recess fit take the smallest width and the longest drop. A 6 mm difference across a 1,200 mm opening is common in older Cape Town homes and is enough to jam a blind that was measured once in the middle.
Reveal Depth Decides What Fits
Depth is the measurement most people skip. A standard roller tube and bracket needs about 55 mm of depth to sit fully inside the reveal; a 50 mm venetian needs roughly 70 mm to stack without fouling the frame; a cassette or pelmet needs 90 mm or more. Below those figures the blind must be face fitted.
Where Measuring Goes Wrong
- Measuring in centimetres. Blinds are manufactured to the millimetre. 120.5 cm is ambiguous; 1,205 mm is not.
- Deducting a tolerance yourself. The workroom already deducts. Deduct twice and you get a 20 mm light gap.
- Measuring the old blind. The old blind may have been wrong. Measure the opening.
- Ignoring handles and stays. A window handle that protrudes 40 mm into the reveal will stop a recess-fitted blind closing.
- Forgetting the control side. Decide which side the chain or wand goes before ordering.
When to Let an Installer Measure
A free on-site measure removes the risk entirely, because the person measuring carries the responsibility for the fit. That is how blind installation in Cape Town is normally quoted — the measure is part of the job, not an extra. If you are ordering blackout blinds, where a millimetre of light gap is visible at 5am, it is worth insisting on it. Once the measure is done, blind lead times sets out how long manufacture and fitting take.
Frequently Asked Questions
Should I measure in millimetres or centimetres?
Millimetres, always. Every blind workroom manufactures to the millimetre, and a rounded centimetre figure introduces up to 5 mm of error before the blind is even made.
Do I deduct anything from my measurements?
No. Supply the exact opening size and state whether it is a recess or face fit. The manufacturer applies the deduction, typically 3–5 mm total on a recess fit.
How deep does a window reveal need to be for a recess fit?
About 55 mm for a standard roller blind, 70 mm for a 50 mm venetian, and 90 mm or more if you want a cassette or pelmet. Anything shallower should be face fitted.
Get a Free Measure & Quote in Cape Town
Window Blinds Cape Town measures, manufactures and installs across the metro. Call 081 411 8471 or WhatsApp us for a free on-site measure and quote, or see what blinds cost in Cape Town.