How to Measure for Roller Blinds: Step-by-Step Guide

Getting accurate measurements is the most important step when ordering made-to-measure roller blinds. Measure incorrectly, and your beautiful new blinds won’t fit properly-leaving gaps, blocking mechanisms, or simply looking wrong.

The good news? Measuring for roller blinds is straightforward when you know what to do. At Dublin Blinds, we’ve helped thousands of Irish customers measure their windows, and we’ve condensed that expertise into this comprehensive guide. Follow these steps, and you’ll get a perfect fit every time.

What You’ll Need

Before starting, gather these essential tools:

• Steel tape measure: More accurate than fabric tape measures
• Pen and paper: To record measurements immediately
• Step ladder: If needed to reach the top of your windows safely
• Spirit level: Optional but helpful for checking window squareness

Pro tip: Use a steel tape measure at least 3 metres long. Short tape measures require multiple readings, increasing error risk.

Inside Mount vs Outside Mount: Which to Choose

Before measuring, you need to decide how your blind will be mounted. This affects both measurement method and final appearance.

Inside Mount (Recess Fit)

The blind sits inside the window recess, flush with the wall. This creates a clean, built-in look.

Requirements:

• Minimum recess depth of 4cm (6cm+ is ideal)
• Recess walls must be relatively square
• No handles, locks, or keys that protrude into the space

Benefits:

• Clean, minimalist appearance
• Doesn’t encroach on room space
• Shows off decorative window frames

Drawbacks:

• Small light gaps around edges
• Requires suitable recess depth
• Can make windows appear smaller

Outside Mount (Face Fit)

The blind attaches to the wall or window frame above the recess, covering the entire window area.

Requirements:

• Flat surface above window for brackets
• Enough wall space around window

Benefits:

• Better light blocking (no side gaps)
• Makes windows appear larger
• Works with any window style
• Hides unsightly window frames

Drawbacks:

• Blind visible even when rolled up
• Takes up wall space

Our Recommendation

For bedrooms where maximum darkness matters, choose outside mount. For living spaces where you want a clean look, inside mount often looks best-providing your recess is deep enough.

How to Measure for Inside Mount

Inside mount measurements are straightforward, but precision is essential.

Step 1: Measure the Width

1. Measure the width of the window recess at three points: top, middle, and bottom
2. Record all three measurements
3. Use the smallest measurement-this ensures the blind fits

Important: Measure the exact recess width. We’ll make the blind slightly narrower (typically 10mm less) to allow for smooth operation.

Step 2: Measure the Height

1. Measure the height at three points: left, middle, and right
2. Record all three measurements
3. Use the smallest measurement

Important: Measure from the top of the recess to the window sill. If there’s no sill, measure to where you want the blind to end.

Step 3: Measure the Recess Depth

1. Measure from the window glass to the front edge of the recess
2. Check at multiple points as depth can vary

Minimum requirements:

• Standard roller blind: 4cm minimum depth
• Blackout roller blind: 5cm minimum (thicker cassette)
• Ideal for smooth operation: 6cm+

If your recess is too shallow, you’ll need an outside mount instead.

Step 4: Check for Obstructions

Look for anything that might interfere with the blind:

• Window handles or locks
• Trickle vents at the top of the window
• Keys left in locks
• Tile edges or uneven plaster

Note the position of any obstructions so we can advise on solutions.

How to Measure for Outside Mount

Outside mount gives you more flexibility-you decide how much coverage you want.

Step 1: Measure the Width

1. Decide how much overhang you want on each side (typically 5-10cm)
2. Measure the window recess width
3. Add your desired overhang to each side

Example: Window recess is 80cm + 7cm left overhang + 7cm right overhang = 94cm total width

Minimum recommendation: At least 5cm overhang each side for effective light blocking.

Step 2: Measure the Height

1. Decide where the blind will be mounted (above the recess or on the frame)
2. Measure from your chosen mounting point to where you want the blind to end
3. For maximum light blocking, extend 5-10cm below the window sill

Example: Mounting 10cm above recess + 100cm recess height + 5cm below sill = 115cm total drop

Step 3: Check the Mounting Surface

• Ensure the surface is flat and sturdy enough for brackets
• Check for pipes, wires, or other hidden obstacles
• Note if you’re mounting to plaster, brick, or wood (affects fixings needed)

Step 4: Consider the Roll Direction

For outside mount, you can choose:

• Standard roll: Fabric hangs behind the roller tube (recommended)
• Reverse roll: Fabric hangs in front of the tube (sits closer to window)

Common Measuring Mistakes to Avoid

After years of fitting blinds across Dublin and Ireland, these are the mistakes we see most often:

Mistake 1: Measuring Only Once

The problem: Windows aren’t always perfectly square. A single measurement can miss variations.

The solution: Always measure at three points (top, middle, bottom for width; left, middle, right for height).

Mistake 2: Using the Wrong Tape Measure

The problem: Fabric tape measures stretch, phone apps aren’t accurate enough, and guessing is never a good idea.

The solution: Use a proper steel tape measure for all measurements.

Mistake 3: Rounding Up

The problem: Adding a few millimetres \”just in case\” can mean a blind that doesn’t fit in the recess.

The solution: Measure exactly and let us make the appropriate deductions for fitting clearance.

Mistake 4: Forgetting Obstructions

The problem: A window handle that sticks out 3cm can completely block an inside-mounted blind.

The solution: Check for handles, locks, vents, and any other protrusions before ordering.

Mistake 5: Not Checking Recess Depth

The problem: Ordering inside mount blinds for a recess that’s too shallow means they won’t fit or operate properly.

The solution: Always measure recess depth and compare to minimum requirements.

Special Window Situations

Bay Windows

Bay windows require individual measurements for each section. Measure each window separately, and note:

• Angles between windows
• Whether blinds will overlap or have gaps
• Any joins or mullions between panes

For complex bays, we recommend a free home consultation to ensure perfect results.

Velux/Skylight Windows

Roof windows have specific requirements:

• Note the window model number (usually on the frame)
• Measure the glass area only
• Specialist fittings are needed-contact us for skylight blinds

French Doors and Patio Doors

• Measure each door panel separately
• Check clearance for door handles
• Consider whether blinds will interfere when doors open
• Low-profile headrails work best for doors

Arched or Shaped Windows

Standard roller blinds don’t suit curved windows. For arched windows, consider:

• Mounting a standard blind below the arch
• Custom-shaped blinds (contact us for options)
• Alternative window treatments

Recording Your Measurements

Use this format to record measurements for each window:

Measurement Template

Window Location:
[e.g., Master Bedroom - Main Window]
Mount Type: Inside / Outside

WIDTH:
Top: _____ mm
Middle: _____ mm
Bottom: _____ mm
→ Use smallest: _____ mm

HEIGHT:
Left: _____ mm
Middle: _____ mm
Right: _____ mm
→ Use smallest: _____ mm

RECESS DEPTH: _____ mm

OBSTRUCTIONS:
[ ] Window handles
[ ] Trickle vents
[ ] Other: _____

NOTES: ______________________________

Pro tip: Take photos of each window with measurements written on paper held in frame. This helps avoid mix-ups when ordering multiple blinds.

Tips for Ordering
Once you have your measurements, here’s what to know when ordering:

Provide Exact Measurements

At Dublin Blinds, we make the appropriate deductions for fitting clearance. Give us your exact recess size-don’t try to calculate deductions yourself.

Double-Check Before Ordering

Made-to-measure blinds are manufactured specifically for your windows. Re-measure to confirm before finalising your order.

Consider Professional Measuring

If you’re unsure or have complex windows, our free measuring service takes the stress away. We’ll:

• Measure all windows accurately
• Advise on the best mount type
• Identify any potential issues
• Provide a no-obligation quote

Book your free measuring visit today.

Get It Right First Time

Accurate measurements are the foundation of perfectly fitting roller blinds. Take your time, measure at multiple points, and don’t hesitate to ask for help with complex windows.

Remember:

• Measure width and height at three points each
• Always use the smallest measurement
• Check recess depth for inside mount
• Note any obstructions
• When in doubt, book a free measuring visit

With proper measurements, your new roller blinds will fit beautifully and operate smoothly for years to come.