How to Measure for Blinds (and the 7 Mistakes That Cost You Time and Money)
She had waited weeks for her new no-drill roller blind. Measured the window herself. Placed the order, chose the perfect fabric, tracked the delivery. When the parcel arrived she could barely wait to fit it. Then she held it up to the window and her heart sank. Too short. A gap at the bottom that let in all the light she was trying to block.
How do you measure windows for blinds correctly in South Africa?
- Use a steel tape measure, never a phone app or cloth tape, and measure in millimetres
- Measure width at three points (top, middle, bottom) and use the narrowest measurement
- Measure height at three points (left, centre, right) and use the longest measurement
- Decide between inside mount (within the recess) and outside mount (on the wall) before measuring — each method requires different dimensions
- Never assume two windows are the same size, even if they look identical — South African homes settle over time and frames shift
- Do not make deductions for brackets or clearance — Custom Blinds handles factory deductions based on your exact measurements
- Custom Blinds offers a Custom Fit Guarantee: too big, we trim for free; too small, we remake at a discount
Need measuring help? WhatsApp us on 076 022 8410 — send a photo and we will check your measurements before you order
TLDR
Use a steel tape measure, measure width and height in three places each, record in millimetres, and do not deduct for brackets. Most measurement mistakes come from using a phone app instead of a metal tape, measuring only once, or confusing inside mount with outside mount. Custom Blinds checks your measurements before manufacturing and our Custom Fit Guarantee covers you if something goes wrong.
Why This Matters
Ordering blinds online is exciting. You have chosen the fabric, imagined how the room will look, and counted the days until delivery. The last thing anyone wants is to open the box and discover the blind does not fit. That sinking feeling is avoidable. Every time.
We see it regularly. A customer in Cape Town used her iPhone measure app and the blind arrived 40mm too short. An elderly couple in Durban measured once instead of three times and their venetian would not sit level. A homeowner in George assumed all four bedroom windows were the same width — they were not. These are not careless people. They are people who were not told what to watch out for.
“People do not get measurements wrong because they are bad at DIY. They get them wrong because nobody explained the difference between measuring the window and measuring for the blind. Those are two different things.”
Duncan, Custom Blinds — 15 years installing across the Garden Route
Your Safety Net
What Happens When a Measurement Goes Wrong
With most online blind retailers, a wrong measurement means a blind you cannot use and money you cannot get back. Custom-made products are not returnable at most companies. We do it differently because we know mistakes happen.
Too Big? Free Trim
If your blind arrives too wide, send it back or we collect it. We cut it down and return it, usually within a day. No charge for the trim.
Too Small? Discounted Remake
If the blind is too short or too narrow, we remake it at a 5% discount. You cover the courier cost. We have even sent customers a free metal tape measure to prevent it happening again.
Installations Since 2010
We have fitted blinds in old Cape Dutch homes, new Plettenberg Bay estates, and everything in between. We know how South African windows behave.
The 7 Most Common Measuring Mistakes (and How to Fix Each One)
These are the mistakes we see most often from online orders. Each one is fixable before you order — if you know what to look for.
Mistake 1: Using a Phone App Instead of a Metal Tape Measure
Phone measurement apps use the camera and augmented reality to estimate distances. The technology is improving but it is not accurate enough for blinds. We recently had a customer who measured her window with the Apple Measure app. The blind arrived too short. She was so excited about fitting it herself — and so disappointed when it did not reach the sill. We remade the blind and sent her a small metal tape measure with the replacement so it would not happen again.
Phone apps can be off by 10–20mm or more. That is the difference between a blind that fits and one that leaves a light gap at the bottom.
The fix
Use a steel tape measure. A basic one from any hardware shop costs under R50 and lasts for years. Cloth sewing tapes stretch. Phone apps guess. Metal tapes give you the actual number.
Mistake 2: Measuring Only Once
Windows are rarely perfectly square. Houses settle. Plaster is uneven. Wooden frames swell in humid coastal air. If you measure only at the top of the window, you might miss that the bottom is 8mm narrower — and your blind will scrape or jam.
The fix
Measure the width in three places: top, middle, and bottom. Measure the height in three places: left, centre, and right. For inside mount, record the narrowest width and the longest height. This ensures the blind fits through the tightest point and covers the full opening.
Mistake 3: Assuming All Windows Are the Same Size
This one catches people in bedrooms and living areas where the windows look identical. You measure one window, order four blinds in that size, and discover that one frame is 12mm wider and another is 6mm shorter. Suddenly two blinds fit well and two do not.
The fix
Measure every single window separately. Label each one clearly — “Master bedroom left”, “Master bedroom right” — so you do not mix them up when ordering. Even a few millimetres matter on a made-to-measure blind.
Mistake 4: Confusing Inside Mount and Outside Mount
Inside mount blinds sit within the window recess for a clean, built-in look. Outside mount blinds fix to the wall or frame and extend past the opening for better light blocking. Each requires a completely different set of measurements. If you measure for inside mount but your recess is too shallow (less than 40mm deep for most roller blinds), the brackets will not fit inside.
The fix
Decide your mount type before you pick up the tape measure. For inside mount, check the recess depth first. For outside mount, add at least 50mm overlap on each side and 50mm above the opening to block light gaps. Our measuring guide has diagrams for both.
Mistake 5: Making Your Own Deductions
Some customers try to account for bracket clearance or roller tube diameter by subtracting a few millimetres from their measurement. The intention is good but the result is a blind that arrives too small. Every blind type has different factory deductions — roller blinds, venetians, honeycomb shades — and the factory knows exactly how much to subtract.
The fix
Give us the exact window measurement. Do not round down. Do not subtract anything. We handle the deductions at the factory based on the specific product you have ordered.
Mistake 6: Mixing Up Width and Height
It sounds too simple to get wrong, but transposing width and height is one of the most common errors in the industry worldwide. You write down 1200 x 900 when you meant 900 x 1200, and you end up with a blind that is wider than it is tall when it should be the other way around.
The fix
Always record width first, then height. Write a “W” next to the width number and an “H” next to the height. When ordering on shop.customblinds.co.za, the form asks for width and height separately — double-check them before you submit.
Mistake 7: Measuring Existing Blinds Instead of the Window
If you already have blinds and want to replace them, it is tempting to measure the old blind and order the same size. But the old blind may have been wrong to begin with. It may have been trimmed. Different products have different factory deductions so a venetian blind and a roller blind with the same window measurement will arrive at different finished sizes.
The fix
Always measure the window opening, not the existing blind. Take down old blinds or curtains before measuring so you have a clear, unobstructed window frame to work with.
Inside Mount vs Outside Mount: Which Measurements Do You Need?
Choosing the right mount type is half the battle. Here is a clear comparison of what each option requires.
| Factor | Inside Mount | Outside Mount |
|---|---|---|
| Where it fits | Within the window recess | On the wall or frame face |
| Width measurement | Inside recess — use narrowest of 3 | Overall coverage area — add 50-100mm overlap per side |
| Height measurement | Inside recess — use longest of 3 | From mounting point to desired end point |
| Minimum recess depth | 40mm for most roller blinds, 60mm for venetians | Not applicable — mounts on flat surface |
| Light blocking | Small gaps at edges are normal | Better light block with adequate overlap |
| Visual effect | Clean, built-in, minimalist | Window appears larger, covers imperfections |
| Measurement forgiveness | Less forgiving — precision matters | More forgiving — overlap hides small errors |
| Best for | No-drill blinds, deep recesses, paired with curtains | Shallow recesses, maximum light block, bedrooms |
Step-by-Step: How to Measure for Roller Blinds
Roller blinds are our most popular product for online orders. This method works for both blockout and light-filtering roller blinds in inside or outside mount.
What You Need
- Steel tape measure (not cloth, not a phone app)
- Pencil and paper or your phone’s notes app to record numbers
- Step ladder if the window is above head height
- A clear window — remove old blinds, curtains, and anything on the sill
For Inside Mount
→
→
→
Measure width from inside edge to inside edge at the top, middle, and bottom of the window recess. Record the narrowest number. Then measure height from the top of the recess to the sill at the left, centre, and right. Record the longest number. That is your order size. Do not subtract anything.
For Outside Mount
→
→
→
Measure the total area you want the blind to cover, including overlap. Add at least 50mm per side beyond the window opening to minimise light gaps. For the height, measure from where the brackets will sit (typically 50–100mm above the opening) down to the sill or your desired finish point.
Last month a customer’s roller blind arrived too wide. We collected it, cut it down, and returned it the next day. No charge. That is what the Custom Fit Guarantee is for.
Measuring Tips by Blind Type
Different blinds have different requirements. Here is what to watch for with each type we sell online.
| Blind Type | Key Measuring Note | Min Recess Depth |
|---|---|---|
| Roller Blinds | Width measured edge to edge. Factory deducts for brackets. | 40mm |
| No-Drill Roller Blinds | Tension brackets need at least 40mm depth. If width varies by more than 6mm across 3 measurements, contact us first. | 40mm |
| Venetian Blinds | Account for handle and latch protrusions inside the recess. Slat stack height reduces visible glass when raised. | 60mm |
| Honeycomb Blinds | Same method as rollers. Cell structure means minimal stack when raised. | 45mm |
| Outdoor Blinds | Reveal fit or face fit — measure all four corners as heights may differ for drainage. Check top and bottom widths separately. | N/A (face mount) |
“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, Custom Blinds — over 8 000 installations across the Garden Route
Getting It Right First Time
Your Pre-Order Measuring Checklist
Run through this list before you submit your order. It takes two minutes and prevents the most common problems.
Steel Tape
Metal tape measure, not a phone app, cloth tape, or ruler. Measure in millimetres.
3 × 3 Rule
Three width readings, three height readings. Use narrowest width, longest height for inside mount.
Label Each Window
Room name + position. “Kitchen left”, “Lounge bay centre”. Match labels to your order.
Photo Check
WhatsApp us a photo with the tape measure visible. We confirm before manufacturing.
Frequently Asked Questions
Can I use my phone to measure windows for blinds?
Phone measurement apps can be off by 10–20mm or more, which is enough to cause a poor fit. Always use a steel tape measure for blinds. If you only have your phone, use it to take a photo of the window with a tape measure held across it and send it to us on WhatsApp for verification.
What happens if my blinds arrive and they do not fit?
Custom Blinds offers a Custom Fit Guarantee on online shop orders. If the blind is too big, we trim it down for free. If it is too small, we remake it with a 5% discount — you only cover courier costs. Contact us on 076 022 8410 and we will sort it out quickly.
Do I measure in centimetres or millimetres?
Millimetres. A blind that is 5mm off in centimetre rounding can create a noticeable gap or a blind that will not fit into the recess. Millimetres give you the precision that custom-made blinds require.
How do I measure for blinds in South Africa with non-standard windows?
Many South African homes, especially older properties on the Garden Route, have windows that are not perfectly square due to settling or handmade frames. Measure in three places for both width and height, and send us photos if anything looks unusual. Our team has fitted blinds in homes from 1920s cottages to new-build estates and can advise on the best approach.
Should I deduct anything from my measurements for brackets?
No. Provide the exact window measurement. Different blind types require different factory deductions and the manufacturing team applies these automatically. Subtracting your own clearance is one of the most common causes of blinds arriving too small.
What is the minimum recess depth for inside mount roller blinds?
Most roller blinds need at least 40mm of recess depth for the brackets and roller tube to fit inside the window frame. If your recess is shallower than 40mm, an outside mount is the better option. No-drill roller blinds also require 40mm depth for the tension brackets to grip.
Can Custom Blinds help me check my measurements before I order?
Yes. Send a photo of your window with the tape measure visible to our WhatsApp line on 076 022 8410. We will confirm your measurements and mounting type before manufacturing begins. This service is free and has prevented hundreds of remakes.
Ready to Order?
Measure your windows, check them twice, and let us handle the rest. Or send us a photo and we will check them for you.
Custom Blinds Shutters & Awnings™ — Garden Route, South Africa. Custom Fit Guarantee applies to online shop orders only. Prices and lead times subject to change. Always measure in millimetres using a steel tape measure.
