How to Measure for Vertical Blinds Like a Pro

When it comes to installing vertical blinds, precision is everything. Even a small measuring mistake can lead to blinds that don’t fit properly, sag awkwardly, fail to provide the privacy you need, or allow unwanted slivers of light to creep in. The difference between a polished, professional finish and a frustrating, imperfect result often comes down to how well you measure your windows.

Accurate measurements not only ensure your vertical blinds fit seamlessly — they also guarantee optimal light control, maximum privacy, and a clean, tailored appearance. Whether you’re covering a wide patio door, a large picture window, or a simple kitchen window, taking the time to measure correctly will save you hassle and disappointment down the line.

Your Step-by-Step Guide to Measuring for Success

In this definitive guide, we’ll walk you through exactly how to measure for vertical blinds — like a pro. From understanding your window type to knowing where to measure and what tools you need, we’ll cover every detail to help you achieve the perfect fit. Whether you’re planning a DIY installation or preparing to order made-to-measure vertical blinds from DotcomBlinds, you’ll be equipped with all the know-how you need.

Why Vertical Blinds Are So Popular

Vertical blinds remain one of the most popular window treatments for good reason:

• Versatility: Available in a huge range of colours, textures, and finishes to suit any decor style.
• Ideal for Large Windows & Patio Doors: Their vertical slats glide smoothly across wide openings, making them perfect for covering floor-to-ceiling glazing, sliding doors, and large windows.
• Excellent Light Control: Tilt the slats to adjust the angle of light entering your room, or draw them fully to one side for an open view — vertical blinds offer precision light management.
• Privacy on Demand: Instantly create privacy without sacrificing natural light during the day.

Whether you’re enhancing a contemporary living room, adding functionality to a home office, or dressing large patio doors in your kitchen-diner, vertical blinds offer style, practicality, and performance — provided they’re measured and installed correctly.

Essential Preparation – Setting Yourself Up for Success

Before you take a single measurement, it’s important to get properly prepared. The more organised you are, the more accurate your measurements will be — and the smoother the entire process will feel. Here’s how to set yourself up for success.

Tools You’ll Need (and Why)

Having the right tools on hand makes all the difference:

Steel Measuring Tape

• Use a steel measuring tape — not a cloth tape — as it provides accurate, rigid measurements that won’t sag or stretch.
• For larger windows, choose a tape that’s at least 5–8 metres long, so you can measure wide spans without running out of length.

Pencil / Pen

• Use a pencil or pen to make light marks where needed and to record your measurements clearly.

Paper / Notebook

• It sounds simple, but having a dedicated notebook or printed measurement sheet helps prevent costly mix-ups.
• Clearly label each measurement (Width, Drop/Height) and note whether it’s for inside or outside mount.

Step Ladder (if necessary)

• For high windows, use a sturdy step ladder so you can reach the top of the recess comfortably and safely.
• Don’t overstretch — always reposition the ladder as needed.

Spirit Level (optional but recommended)

• A spirit level is handy to check whether your window recess is level — if it’s not, you may need to adjust your fitting measurements slightly for a professional look.

Second Person (highly recommended)

• For large or wide windows, having a second person hold the tape measure steady at one end ensures you achieve perfectly straight, accurate measurements.
• This simple step helps avoid sagging tape or uneven results.

Understanding Key Terminology

Before you start measuring, it’s helpful to understand some key terms used when ordering vertical blinds:

Recess

• The opening within your window frame where the glass and frame sit.
• For an inside/recess fit, your blind will be installed within this space.

Exact / Outside Mount

• This refers to fitting your blind outside the recess, so it covers the entire window frame and extends beyond it.
• Useful when the recess is too shallow or when complete light block is desired.

Width (W)

• The horizontal measurement across the window or recess.

Drop / Height (H)

• The vertical measurement from top to bottom of the window or recess.

Headrail

• The top track that holds the blind’s mechanism and supports the louvres (slats).

Louvre / Slat

• The individual vertical fabric strips that make up the blind.

Stack

• The side where the louvres gather when the blind is open:

  • Left stack

  • Right stack

  • Split stack (equal stack on both sides of the window)

Knowing these terms will help you communicate clearly when ordering your vertical blinds and ensure you select the right options.

Safety First

A quick but essential reminder — safety matters:

• If using a step ladder, make sure it’s positioned on a flat surface and fully opened with all safety locks engaged.
• Always be aware of your surroundings — avoid working near open windows, children, or pets when on a ladder.
• If in doubt, ask your second person to steady the ladder or spot you.

Choosing Your Mounting Style – Inside vs. Outside Recess

Before you start measuring, you’ll need to make a crucial decision — will your vertical blinds be mounted inside the window recess, or outside of it? This choice will dictate your entire measuring process and ultimately affect how your blinds look and perform.

Inside Recess (Recess Fit)

If you choose an inside recess fit, your blinds will sit within the window frame, neatly aligned with the edges of the recess. This is a popular option for creating a sleek, integrated look.

Pros:

• Provides a neat, flush appearance that showcases the architecture of your window.
• Ideal for windows with decorative architraves or a window sill you want to display.
• Keeps the blind neatly contained — great for small spaces where minimal protrusion is desired.

Cons:

• The stacked louvres can block more of the view and light when open compared to an outside mount.
• Requires sufficient recess depth to accommodate the headrail and louvres — typically at least 6–7 cm is recommended for a smooth operation and clean finish.
• May not be suitable for windows with significant obstructions or uneven recesses.

When to Choose Inside Recess:

• You want the blind to sit within the window frame for a tailored, built-in look.
• You have a deep enough recess to allow the blind to operate without obstruction.
• You’d like to show off your window features, such as decorative trim, architraves, or a beautiful window sill.

Outside Recess (Exact / Face Fit)

With an outside recess fit, the blind is mounted above and beyond the window frame, covering part of the surrounding wall. This approach is fantastic for achieving a grander visual effect or dealing with tricky window structures.

Pros:

• Maximises light and view when the blind is stacked, as the louvres can move fully clear of the window glass.
• Can make a window appear larger and more prominent.
• Ideal for windows with shallow recesses, uneven frames, or obstructions (such as handles or vents).
• Offers the best light block — perfect for bedrooms or media rooms where you want to minimise light bleed.

Cons:

• The blind will cover part of the wall surrounding the window.
• The headrail and stacked louvres may protrude slightly into the room — worth considering in smaller spaces.

When to Choose Outside Recess:

• Your window recess is too shallow to accommodate a full recess fit.
• There are obstructions within the window recess (handles, locks, vents).
• You want maximum light block or a more dramatic window treatment.
• You’d like to make the window appear larger or taller than it really is.

In short:

Pro Tip: If you’re unsure which mounting style is best for your space, take a few moments to visualise both options. Consider how the blinds will look when fully open and fully closed — and always check your recess depth carefully before committing to an inside fit.

Step-by-Step Measuring Guide – Recess Fit (Inside the Window Frame)

If you’ve decided to go for an inside recess fit, careful and accurate measuring is absolutely essential to achieve that sleek, professional finish. Here’s exactly how to do it.

The Golden Rule for Recess Fit

Always take three measurements for both width and drop — and use the smallest of each.

Why?
Because even if your windows look perfectly square, most aren’t. Walls can bow, sills can tilt, and frames can shift over time. Taking three measurements ensures your new blinds will fit the narrowest and shortest points — preventing unsightly gaps, bunching, or blinds that don’t hang correctly.

Measuring Width

Follow these steps to measure the width (left to right) of your window recess:

1. Measure across the top of the recess
   Place your steel tape measure as close to the top as possible and measure straight across.
2. Measure across the middle of the recess
   Measure horizontally across the centre of the recess.
3. Measure across the bottom of the recess
   Measure horizontally just above the window sill.
4. Record the smallest of the three measurements
   This ensures your blind will fit even if the recess is slightly narrower at one point.

Deductions:

You do not need to make any deductions yourself!
Reputable blind manufacturers, such as DotcomBlinds, will automatically apply a small deduction (usually around 10–15 mm) to allow for smooth operation and clearance.
👉 Simply provide the ‘tight’ recess measurement — your manufacturer will take care of the rest.

Measuring Drop / Height

Now measure the drop (top to bottom) of your window recess:

1. Measure from the top of the recess to the window sill on the left
   Place your tape measure at the very top of the recess and measure straight down to the sill.
2. Measure from the top of the recess to the window sill in the middle
   Measure vertically down the centre of the recess.
3. Measure from the top of the recess to the window sill on the right
   Measure vertically down the right side of the recess.
4. Record the smallest of the three measurements
   This prevents your blind from dragging on the sill or hanging unevenly.

Deductions:

Again, you should not make any deductions.
The manufacturer will ensure the louvres are sized so they hover neatly above the sill — typically leaving a small gap to prevent wear and tear or obstruction.
👉 Always supply the exact ‘tight’ recess height measurement — the manufacturer will handle the rest.

Quick Recap:
✅ Take three measurements across the width and height.
✅ Always use the smallest measurement.
✅ Do not make your own deductions — provide exact recess sizes.
✅ Clearly label your measurements as recess fit when ordering.

Step-by-Step Measuring Guide – Exact/Face Fit (Outside the Window Recess)

If you’ve chosen an outside recess fit (also known as exact fit or face fit), your measuring approach is a little different. The key here is that you’ll be deciding exactly how much of the surrounding wall you want your blind to cover.

The Golden Rule for Exact Fit

For exact fit, you should measure the exact area you want the blind to cover — and supply that full measurement.

👉 The manufacturer will make no deductions from this measurement. Your blind will be made to the exact width and drop you provide.

Measuring Width

1. Decide your overlap
   Choose how much you’d like the blind to overlap the window recess on each side. We recommend at least 5–10 cm (2–4 inches) of overlap on each side. This ensures:

   • Better light block

   • Improved privacy

   • A more visually balanced appearance

2. Measure the actual window opening width
   Use your steel tape measure to measure the width of the window opening itself.

3. Add your desired overlap
   Add your chosen overlap to both sides of the window.
   Example:

   • Window width = 100 cm

   • Overlap: 5 cm left + 5 cm right

   • Total width to order = 110 cm

4. Record this total measurement
   Write it down clearly — this is the width you will provide when ordering your exact fit vertical blind.

Consider Obstructions:

Before finalising your width, check for potential obstructions:

• Light switches
• Door frames
• Wall units or shelves
• Furniture near the window

Ensure that the blind, when stacked open, won’t interfere with these elements.

Measuring Drop / Height

1. Decide where you want the headrail to sit
   For the best look and to help block light, it’s common to position the headrail 5–10 cm above the window recess. This also adds a grander, more elegant appearance.
2. Decide where you want the louvres to finish
   Think about the lower end of the blind:
3. Just touching the floor — ideal for patio doors.
4. Hovering above a radiator — leave a clearance of about 2–3 cm to avoid heat damage and allow airflow.
5. Covering the entire window frame — if not full length.
6. Measure from your desired headrail position to your desired finishing point
   Place your tape measure at the point where the top of the headrail will be mounted.
   Measure vertically to your desired bottom point.
7. Record this total measurement
   This is the exact drop you will provide when ordering your blind.

Consider Obstructions:

Again, take note of any obstructions in the drop path:

• Radiators — leave a gap so the blind doesn’t rest directly on the radiator.
• Window sills — decide if you want to finish above or below.
• Furniture — ensure the blind can move freely.

Quick Recap:
✅ Measure the total area you want the blind to cover.
✅ No deductions — supply full width and height.
✅ Think about overlap and headrail/finishing positions.
✅ Watch out for obstructions.

Crucial Considerations & Pro Tips for Vertical Blinds

Now that you know how to measure, here are some important final considerations and pro tips to help you avoid common mistakes and achieve that perfect result.

Recess Depth

Why It Matters

If you’re choosing an inside recess fit, your recess needs to be deep enough to accommodate the vertical blind’s headrail and ensure the louvres can hang and operate freely.

• Typical minimum recess depth: 6–7 cm (always check your specific blind’s product details).
• Less than this? The headrail may stick out, and the louvres may not rotate smoothly.

What If the Recess Is Too Shallow?

If your recess is too shallow, consider switching to an outside mount instead. This ensures:

• The blind operates smoothly.
• The headrail is mounted securely.
• You avoid the frustration of a tight, poorly functioning fit.

Pro Tip: Always measure the depth of the recess before deciding on a recess fit.

Obstructions

Window Handles / Cranks

• Check whether the blind will clear the handles when fully closed and when rotated.
• If not, consider:

• • Outside mount.

  • Extension brackets to bring the blind forward.

Vents / Airbricks

• Be mindful of vents or airbricks that could obstruct louvre movement.
• For face-fit blinds, position the blind to avoid them where possible.

Radiators / Furniture

• If you’re installing floor-length blinds, make sure they clear any radiators or furniture underneath.
• Leave about 2–3 cm gap above a radiator to avoid heat damage and allow airflow.

Stacking Options

Where your louvres stack when open has a big impact on both function and aesthetics:

Left Stack

• Louvres gather on the left side when open.
• Useful if right side access is needed (e.g. door opens on the right).

Right Stack

• Louvres gather on the right side when open.
• Useful if left side access is needed.

Split Stack (Centre Open)

• Louvres gather evenly on both sides — just like curtains.
• Excellent for centred views or patio doors where you want equal access from both sides.

Consider the View & Traffic

• Think about where your best view lies — you don’t want the stack blocking it.
• Consider door opening direction — avoid stacking on the side where the door opens, to maintain clear access.

Control Side

Decide whether you’d like the pull cord / chain / wand on the left or right side.

Consider:

• Which side is more convenient to reach.
• Which side has fewer obstructions (radiators, furniture, etc.).
• Personal preference.

Fabric Choices & Their Impact on Measurement (Slightly)

Weighted vs. Sewn-in Weights

• Some louvres use sewn-in weights for a clean look.
• Others have bottom pockets with removable weights and stabilising chains.

This won’t affect your measuring, but it’s good to know when selecting your fabric — particularly if you want a clean, contemporary look (opt for sewn-in).

Light-Filtering vs. Blackout

• This also doesn’t affect measuring, but it’s worth reminding yourself of the blind’s purpose.
• Light-filtering fabrics soften and diffuse light — ideal for living spaces.
• Blackout fabrics block light entirely — perfect for bedrooms or media rooms.

Measuring for Bay Windows / Conservatories (Advanced)

Bay windows and conservatories can present more complex measuring challenges.

• For bay windows, angles and projections make accurate measuring tricky — often requiring a template or professional measuring service.
• Similarly, conservatories can have sloping rooflines, uneven reveals, and varying window depths.

Pro Tip:
If you’re planning vertical blinds for a bay or conservatory, refer to a specialist measuring guide or consult an expert to ensure precision.

Double-Check Everything

Finally — the golden rule of measuring:
Measure at least twice — or even three times — to confirm accuracy.

It’s always better to spend a few extra minutes checking your numbers than to end up with blinds that don’t fit. The old adage absolutely applies here:

👉 Measure twice, cut once.

What Information to Provide to the Supplier

When ordering your vertical blinds, here’s the full list of information you’ll need to provide:

✅ Width (W)
✅ Drop / Height (H)
✅ Mounting Type (Recess Fit or Exact/Face Fit)
✅ Stacking Option (Left, Right, Split)
✅ Control Side (Left or Right)
✅ Fabric Choice (including light-filtering or blackout preference)

Tip: Clearly label your measurements and instructions when ordering to avoid confusion — especially if ordering multiple blinds for different windows.

Troubleshooting & Common Mistakes to Avoid

Even with the best intentions, it’s easy to make small measuring errors that can lead to frustrating results. Here’s a quick guide to common mistakes to watch out for — and how to avoid them — so you can measure your vertical blinds like a true pro.

Not Using a Steel Tape Measure

✅ Always use a steel tape measure, not a cloth or flexible tape.

• Steel tape ensures accurate, straight measurements.
• Cloth tapes can stretch or sag, giving false readings — especially across large windows.

Assuming Windows Are Square

✅ Never assume your window is perfectly square or even.

• That’s why we recommend taking three measurements across both width and height.
• Windows often have minor variations — measuring only once can result in a blind that doesn’t fit properly.

Making Deductions Yourself for Recess Fit

✅ Do not make your own deductions when ordering a recess fit blind.

• The manufacturer (such as DotcomBlinds) will make precise allowances so the blind fits and operates correctly.
• If you deduct yourself and the manufacturer also deducts, your blind may end up too small.

👉 Always provide the tight recess measurement — nothing more, nothing less.

Not Allowing Enough Overlap for Exact Fit

✅ For exact/face fit blinds, be sure to allow sufficient overlap on all sides.

• We recommend at least 5–10 cm on each side of the window for optimal light block and a balanced appearance.
• Too little overlap can lead to light gaps and an underwhelming look.

Forgetting About Obstructions (Handles, Radiators)

✅ Always check for and plan around window handles, vents, radiators, furniture, and any other obstructions.

• Failing to do so can result in blinds that don’t clear the handle or rest awkwardly on a radiator.

Pro Tip: Visualise your blind both open and closed when checking for obstructions.

Measuring Only Once

✅ The golden rule: Measure at least twice, ideally three times.

• Double-checking helps catch small mistakes that can otherwise lead to costly re-orders or poor fit.
• It’s worth the extra time for peace of mind.

👉 Measure twice, order once.

Confusing Width and Drop

✅ Clearly distinguish between your width (W) and drop/height (H) measurements.

• It’s surprisingly easy to mix these up when ordering — especially when measuring multiple windows at once.
• Write your measurements clearly and always label them correctly.

Not Writing Down Measurements Clearly

✅ Don’t rely on memory — always write your measurements down immediately.

• Use a dedicated notebook or print out a measuring template.
• Clearly label each measurement, including mounting type (recess or exact), stacking option, control side, and any other notes.

Pro Tip: Keep your notes well organised — you’ll thank yourself when it comes time to order!

Shop Your Vertical Blinds Now

Now that you know exactly how to measure for vertical blinds like a pro, you’re ready to choose the perfect blinds for your space — with complete confidence that they’ll fit beautifully and function just as you want them to.

At DotcomBlinds, we make it easy for you to shop with certainty:

✅ Made-to-measure vertical blinds, crafted to your exact specifications
✅ Huge choice of fabrics, colours, and styles to suit any home
✅ Free fabric samples — so you can see and feel your chosen materials before you buy
✅ Easy online ordering, backed by expert advice and friendly support

Pro Tip: Always order a few free samples first — it’s the best way to explore your fabric options and make sure the colour and texture perfectly match your decor.

Ready to get started?
👉 Head over to DotcomBlinds.com and shop your vertical blinds now — and with your professional measurements in hand, you’ll soon be enjoying stunning blinds that fit and function flawlessly.