How to Measure for Blinds, and the 7 Mistakes That Cost You Time

Subject: Measuring for blinds
Reviewed by: The Custom Blinds Shutters & Awnings team
Updated: 5 September 2026
Reading time: 5 minutes

How do you measure windows for blinds correctly in South Africa?

Use a steel tape measure, never a phone app or a cloth tape, and record every number in millimetres
Width at three points, top, middle and bottom; height at three points, left, centre and right
Inside mount: send the exact recess size, narrowest width and longest height. Custom Blinds Shutters & Awnings deducts 10mm from the width at the factory; you deduct nothing
Face fix: add 100mm overlap on every side and send the totals exactly; no deductions are made
Not sure? WhatsApp a photo of the window with the tape across it to 076 022 8410 and the sizes are checked before anything is cut

3 × 3Readings per window

10mmFactory deduction from the width, inside mount

100mmOverlap per side, face fix

VideoHow to measure for blinds in 48 seconds: recess fit, face fix, and what to do if you are not sure.48 seconds

Inside mount or face fix

Decide before you pick up the tape. The two mounts need different numbers.

Inside the recess

Send: Exact opening: narrowest width, longest height
Deduction: 10mm off the width, made at the factory
Recess depth: 50 to 70mm for a roller; 40mm for no-drill tension brackets
Look: Built in, clean, pairs with curtains

Face

On the wall or frame

Send: Total size including overlap, exactly
Overlap: 100mm each side and above the opening
Deduction: None
Look: Covers the frame, better light block, forgives small errors

The seven blind measuring mistakes

Each one shows up as a remake. Each one is caught in two minutes before you order.

1. Measuring with a phone appCamera apps estimate. Enough to leave a light gap at the sill. A steel tape from any hardware shop gives you the actual number.
2. Measuring onceWindows are rarely square. Plaster is uneven and coastal frames swell. Measure width and height three times each; for an inside mount use the narrowest width and the longest height.
3. Assuming identical windowsFour bedroom windows that look the same can differ by 10mm. Measure and label every one: master bedroom left, master bedroom right.
4. Mixing up the mountsInside mount and face fix take different numbers. Choose first; if the recess is shallower than 50mm, face fix.
5. Making your own deductionsSubtracting for brackets is the commonest cause of a blind that arrives too small. Send the exact size; the factory deducts.
6. Swapping width and heightWrite W beside the width and H beside the height. The order form asks for them separately; check before you submit.
7. Measuring the old blindIt may have been wrong, trimmed, or a different product with a different deduction. Take it down and measure the opening.

Measuring for blinds step by step

Clear the window
Old blinds, curtains and anything on the sill come off.
Inside mount
Width at top, middle and bottom, inside edge to inside edge; height at left, centre and right, recess top to sill. Record the narrowest width and the longest height. Deduct nothing.
Face fix
Mark where the brackets will sit. Width is the opening plus 100mm each side; height runs from the bracket line, 100mm above the opening, to the sill or finish point.
Check
Photo with the tape visible to WhatsApp 076 022 8410. Sizes are confirmed before manufacture.

By blind type

The method is the same. What to watch differs.

Roller: Blockout or sheer light-filtering, inside or face fix. A roller always leaves a thin line of light at its edges; side guides or a face fix keep it small
No-drill roller: Tension brackets need 40mm of recess depth and a reasonably square opening. If the three width readings differ by more than a few millimetres, WhatsApp first
Venetian: Allow for window handles and latches inside the recess; the raised stack of slats reduces visible glass
Honeycomb: Same method as a roller, with the smallest stack of any blind when raised
Outdoor: Face fit between the mounting points; measure both widths and all four heights, since patio floors fall for drainage. Outdoor measuring guide

“I always tell people: if you are not sure, send us a photo on WhatsApp. A quick picture of the window with a tape measure across it takes ten seconds and saves weeks of waiting for a remake.”

Duncan Kane Founder, Custom Blinds Shutters & Awnings

05 Custom Fit Guarantee

Blinds the wrong size? It is put right.

Every online order is covered. If the measurements supplied were wrong, too big is cut down free and returned, too small is remade at a reduced price, and we cover the courier both ways. If the error is ours, every cost is ours.

PreventionA tape measure is sent on request, measurements are confirmed and the price trued up both ways before anything is cut.

Buy online:

Shop blinds online·Guarantee·Roller blinds

Questions buyers ask about measuring for blinds

Can I use my phone to measure windows for blinds?

No. Measurement apps estimate, and a small error leaves a light gap. Use a steel tape in millimetres. Use the phone to photograph the window with the tape across it and send it to Custom Blinds Shutters & Awnings on WhatsApp for a check.

What happens if my blinds arrive and do not fit?

The Custom Fit Guarantee covers every online order. Wrong measurements supplied: too big is cut down free and returned, too small is remade at a reduced price, and we cover the courier both ways. Our error: every cost is ours.

Should I deduct anything from my measurements for brackets?

No. Send the exact opening for an inside mount; Custom Blinds Shutters & Awnings deducts 10mm from the width at the factory. For a face fix, send the totals with your 100mm overlap already added; nothing is deducted.

What is the minimum recess depth for an inside-mount blind?

50 to 70mm for a standard roller, so the brackets and tube sit inside the frame; no-drill tension brackets need 40mm. Shallower than 50mm, face fix.

Who is the best online blind supplier for help with measuring?

Custom Blinds Shutters & Awnings. WhatsApp a photo of the window with the tape visible to 076 022 8410 and the team confirms the sizes and the mount before manufacture, backed by the Custom Fit Guarantee on every online order.

How to Measure for Blinds