How To Measure Windows For Blinds, Curtains, Or Shutters

Precision measurements are the fine line between blinds or internal window treatments that seal perfectly to the edges and frame, and those that don’t scrape or are unable to function. The measuring and installation of bespoke window furnishings across the Central West, the Blue Mountains, and Lake Macquarie have been part of Blinds by Design’s everyday activities for 25+ years. We regularly attend homes throughout Bathurst, Orange, and Belmont and right across the Blue Mountains weekly and can attest that the same measuring errors repeat themselves time and time again.

This guide offers the on-site measuring process we follow in explicit detail for blinds, curtains, and internal plantation shutters.

Quick Answer

All measurements are to be taken using a steel tape measure in millimetres. For inside-fit blinds and internal window coverings, measure the width at the top, centre, and bottom and use the smallest measurement. Measure the height at the left, centre and right and use the shortest. For outside fit measurements, include overlap on the frame measurement. For curtains, measure the track width and height from the track down to the sill or floor. Measure shutter depth and check squareness.

Why Accurate Window Measurements Matter for Blinds and Internal Window Coverings

Australian houses differ more than people think. Census 2021 recorded 10.85 million private dwellings: 70% were separate houses, 13% were townhouses, and 16% were apartments. This blend covers anything from Federation double-hung 1890s timber sash windows in Bathurst with thick timber reveals through to new aluminium-framed shallow Blue Mountains builds all the way to wall-height Lake Macquarie apartments with sliding doors.

The blinds and internal window treatments are all made to measure. As opposed to the generic-sized panels you can buy in the shops, we cannot cut down a roller blind tube or chamfer a shutter frame on site without rendering it useless. If there is a 3 mm inaccuracy in the measurement, it could prevent the blind from fitting at all. That’s why at Blinds by Design we always advise you to ‘measure twice, order once’.

Inside Mount vs Outside Mount: Which Should You Choose?

An inside mount fits within your window recess, creating a streamlined ‘built-in’ finish and showcasing your architraves. They are suitable for rooms where you have sufficient recess depth and a more ‘square’ opening. An outside mount is fixed on the wall or architrave and gives windows a ‘larger’ finish and better light-blocking. Consider an outside mount when you have a shallow recess, an ‘out of square’ window, or are seeking total light blocking.

The inside mount, also referred to as a ‘recess fit’, works best in older ‘Central West’ dwellings with a deep reveal. An outside mount is suitable for contemporary Australian dwellings with ‘slim’ aluminium frames, and also where there is an ‘imperfect’ window to disguise.

Tools You Need Before You Start

• Steel tape measure (not cloth)
• Pencil and notepad or phone
• Step ladder for high windows
• Spirit level to check for square

It is advisable to measure in millimetres, as it is the Australian standard used in the industry, avoiding any conversion errors.

How Do You Measure a Window for Blinds?

Mark the internal width at the top, middle, and bottom of the reveal; note the smaller measurement. Mark the internal height on the left, centre and right and note the smallest measurement. Do not subtract any measurements – our workshop will take care of these. Where external, with no architraves, it will have an extra 50 mm on each side of the width and 90-100 mm on the height for light control.

Here is our whole procedure:

For roller blinds, sunscreen, and light-filtering blinds – inside mount:

1. Measure width, left to right, three times, at the top, in the middle and at the bottom. Note down the smallest of the three.
2. Measure height, at the centre, from the top of the recess to the sill.
3. Measure depth – 60 mm of free depth is required minimum; 70 mm or more is suitable for bigger blinds

For roller blinds – outside mount:

• With architraves: take measurements at the top of the architrave across for the width and from the top of the architrave to the required finish line for the height.
• Without architraves: take a measurement of the opening width and add a minimum of 50 mm for each side. Add 90-100mm to the height.

For timber and PVC venetian blinds – inside mount:

Measure width in 3 places and use the smallest. Measure height left, middle, and right and use the biggest. You must have at least 70 mm depth, more if recessing.

For outside mount Venetians without architraves:

Add 30-40 mm to each side of the width and 90-100 mm to the height.

Label WxH consistently. The most frequent error we see is switching the two.

How Do You Measure a Window for Curtains?

Measure the track or rod width, not the window. Add 150-200mm to either side. For the length, measure from the rod (or top of rings) to your drop: 12 mm above the sill, 150 mm below the sill, 15 mm from the floor, or 300 mm to the puddle. Hang the track 150mm from the top of the window.

Full steps:

1. Make a decision on placement for the track or rod. It is recommended that you place both track and rod 15 cm above the window, allowing for an additional 15-20 cm on each side.
2. Measure the overall width of your track or rod (excluding finials) and take off 5 cm in the centre should you opt for a centre-opening pencil or pinch pleat.
3. Choose your drop:
   • Sill length: finish 1.25 cm above the sill
   • Below sill: 15cm below
   • Floor length: 1.5 cm from the floor
   • Puddle: add 30cm
4. When choosing an eyelet or tab top, measure from the top of the rod; for a ring top for pleats, measure from the bottom of the ring/top of the track.

In a western Sydney apartment with low ceilings, tracks were mounted near the ceiling to achieve height, and in Blue Mountains cottages, under-sill curtains retain heat.

How Do You Measure a Window for Shutters?

To fit internal plantation shutters inside a mount, measure the width at the top, middle, and bottom, and take the narrowest of the three measurements. Measure height at left, middle, and right, and take the shortest of the three measurements. Ensure the recess depth is at least 65-70mm and the two diagonals are the same size. For the outside mount, measure the width and height of the area required to cover, including overlap.

Detailed method:

1. Measure width in 3 places and take the shortest measurement.
2. Measure height in 3 places and take the shortest measurement.
3. Measure both diagonals to check squareness – if the measurement between the two diagonals varies by more than 5 mm, an outside frame is probably needed.
4. Measure depth. Most shutters require a minimum clear space of 65mm (2.5″). Watch out for any protruding handles, locks or window winders

Shutters do not have much tolerance, unlike fabric blinds, as the frame is a solid timber or PVC product. For the Federation houses in Orange, we normally fix them with L-frames that are fixed to the outside, with the out-of-square nature taken into account.

Window Covering Type vs. Measurements Required

Common Measuring Mistakes We See

What mistakes should homeowners avoid?

Only measure with one flexible tape measure at the centre of the window, round to the nearest cm, and calculate the allowance yourself. Always exchange width and height, and disregard any handles that impede the shutters. Always use a steel tape measure, and mark 3 points W x H.

Common Measuring Errors and Their Consequences

When Professional Measuring Is Recommended

• Bay, bow or angled windows
• Internal plantation shutters (less than 2mm tolerance)
• Large openings in excess of 2.4m wide
• Heritage windows (out of square)
• Motorised blinds with power/clearance constraints
• You desire our measure & quote guarantee

We do all measurements as part of our comprehensive service throughout the Central West and Blue Mountains regions. Your home will be measured and checked for depth, squareness, and obstructions to ensure a custom blind will fit the first time, removing any guesswork from the equation.

If you’re unsure about what you are trying to choose between products, read our guide to Blinds vs Curtains vs Shutters: The Ultimate Home Guide. If you are focused on shutters, you can click through to our internal [plantationshutters] page. If you have a choice of fabric, then see our custom curtains range, which details heading styles impacting the measurement.

Need Help Measuring?

If you’d prefer we take the measuring tape for you, that’s exactly what we do day in, day out. Blinds by Design visits to measure and quote throughout Bathurst, Orange, the Blue Mountains & Lake Macquarie – free of charge. We come to your home, look at your windows critically with our samples and do the math, so your blinds, curtains, or internal plantation shutters arrive to fit perfectly.

We invite you to our showrooms at 119a Bentinck Street, Bathurst, or 141 Peisley Street, Orange, or we would be happy to come to your home to show you some solutions. After fitting Australian homes for over 25 years with bespoke window furnishings, we will get it right the first time.

Frequently Asked Questions

How accurate do window measurements need to be?

To the nearest millimetre. Blind and internal window dressings are custom-made for your measurements, and manufacturers only allow 3-5 mm for clearances. 5 mm out will cause the product to bind or leave a gap.

Can I measure windows myself?

Yes, almost all roller, Venetian, and curtain applications use a steel tape measure, also a three-point measurement. For shutters and large windows or irregular windows. Expert measures minimise danger.

Should curtains touch the floor?

Curtains for a floor-to-ceiling finish should be 15 mm off the floor in Australia. For a formal puddle effect, add 300 mm.

How much larger should outside-mount blinds be?

Add a minimum of 50mm to each side (for width) and 90-100mm to height (where there is no architrave). The excess ensures light is blocked out, providing more privacy.

Are shutters measured differently from blinds?

Yes. Shutters require width and height at 3 points at the smallest measurement, with the addition of a 65-70 mm depth measurement and diagonals to ensure it is square. Blinds are slightly more relaxed.