Getting accurate measurements is the single most important step when ordering venetian blinds. Even the highest quality blinds will look amateur and function poorly if they don't fit properly. As someone who has installed thousands of blinds across Australian homes, I can tell you that measurement errors are the number one cause of returns and dissatisfaction.
This guide will walk you through the professional techniques I use to ensure perfect measurements every time.
Before You Start: Gather Your Tools
You'll need a few essential items before measuring:
- A steel tape measure (fabric tapes stretch and give inaccurate readings)
- A pencil and paper or your smartphone for recording measurements
- A step ladder for high windows
- A spirit level (optional but helpful for checking if your window frame is square)
Always measure in millimetres for the most accurate results. Australian blind suppliers work in metric measurements, and converting from centimetres can introduce rounding errors.
Understanding Mount Types
Before measuring, you need to decide how you want your blinds mounted. There are two options:
Inside Mount (Recess Mount)
Inside mount blinds sit within the window recess, providing a clean, built-in appearance. This is the most popular choice for modern Australian homes as it showcases the window frame and creates a streamlined look.
Requirements for inside mount:
- Minimum recess depth of 50mm for aluminium blinds
- Minimum recess depth of 75mm for timber or faux wood blinds
- A relatively square window frame (check with a spirit level)
Outside Mount (Face Mount)
Outside mount blinds are fixed to the wall or window frame above and around the recess. This option is ideal when:
- Your window recess is too shallow for inside mount
- You want to make windows appear larger
- Your window frame is significantly out of square
- You want maximum light blockage
Measuring for Inside Mount
For inside mount installations, you need to measure in three places for both width and height to account for any variations in your window frame.
Measuring Width
- Measure the width at the top of the window recess
- Measure the width in the middle of the recess
- Measure the width at the bottom of the recess
- Record the smallest measurement
The smallest measurement ensures your blinds will fit into the recess without binding against the sides.
Measuring Height
- Measure the height on the left side of the recess
- Measure the height in the centre of the recess
- Measure the height on the right side of the recess
- Record the longest measurement
Using the longest measurement ensures full coverage of your window.
Measuring Recess Depth
Measure from the front of the window frame to the back of the recess. This determines whether your chosen blind type will fit and ensures the blind doesn't protrude beyond the frame.
Most suppliers will make deductions from your inside mount measurements to ensure proper clearance. Check with your supplier whether they want exact recess measurements or if you should make deductions yourself.
Measuring for Outside Mount
Outside mount measurements give you more flexibility as you're deciding how much coverage you want rather than fitting into a fixed space.
Measuring Width
- Measure the total width you want the blind to cover
- For adequate light blockage, add at least 70mm to each side of the window recess
- For maximum coverage, add 100mm to each side
Measuring Height
- Decide where the blind headrail will be mounted above the window
- Measure from that point to where you want the blind to finish
- For windows with sills, measure to 10mm above the sill
- For windows without sills, decide how far below the recess you want the blind to extend
Mounting Position
Measure and record how far above the window recess you plan to mount the headrail. Standard practice is 50-100mm above the recess, but this can vary based on your preferences and any obstructions.
Special Situations
Bay Windows
Bay windows require individual measurements for each section. Measure each window separately and note the angles between sections. Some bay windows may need custom brackets or special consideration for slat clearance when blinds are tilted.
Windows with Handles or Locks
Measure the protrusion of any handles or locks on your windows. For inside mount blinds, you may need to add stand-off brackets to prevent the slats from catching on hardware.
Sliding Doors
For sliding doors, outside mount is usually recommended. Measure the total opening and add overlap on each side. Consider whether you want one large blind or multiple blinds that stack at each end.
Before ordering, verify: measurements are in millimetres, you've noted which mount type, and you've checked for any obstructions like handles or air conditioning units.
Common Measurement Mistakes to Avoid
Mistake 1: Measuring once Always measure at least three times. Window frames are rarely perfectly square, and a single measurement can be misleading.
Mistake 2: Using a fabric tape measure Fabric tapes stretch over time and give inaccurate readings. Always use a steel tape measure.
Mistake 3: Forgetting about obstructions Check for window handles, locks, air conditioning units, or anything else that might interfere with the blind's operation.
Mistake 4: Not accounting for stacking space When raised, venetian blinds stack at the top of the window. Ensure you have adequate headroom if you want an unobstructed view when blinds are fully raised.
Mistake 5: Assuming windows are the same size Even windows that look identical can vary by several millimetres. Measure each window individually.
Recording Your Measurements
Create a simple diagram of each window and label your measurements clearly. Include:
- Width measurement
- Height measurement
- Recess depth (for inside mount)
- Mount type (inside or outside)
- Any notes about obstructions
- Room location for reference
When to Call a Professional
If you have unusually shaped windows, multiple complex installations, or simply want peace of mind, many Australian blind suppliers offer free measure-and-quote services. A professional can identify potential issues you might miss and ensure perfect results.
Taking accurate measurements might seem tedious, but it's time well spent. Properly fitted venetian blinds will operate smoothly, look professionally installed, and serve your home well for many years to come.