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Getting a glass balustrade wrong is an expensive mistake. Glass panels are custom-made and cut to order. Once they are manufactured, they cannot be resized on site. If your measurements are off, you are looking at reordering, additional lead time, and extra cost.

We see this happen more than you might expect. Homeowners measure the floor length and assume that is all they need. They forget to account for post spacing, glass-to-post clearances, and height requirements. The result is panels that do not fit or a system that fails a building control inspection.

In this guide, we walk you through exactly how to measure for a glass balustrade in the UK. We cover flat runs, corners, stairs, and the common mistakes that lead to incorrect orders. Whether you are measuring for a patio, balcony, or indoor staircase, this guide gives you a clear and practical process to follow.

What You Need Before You Start

Measuring for a glass balustrade does not require specialist tools. But having the right equipment makes a real difference to accuracy.

To get started, you will need a pen, paper, and a tape or laser measure. Having someone help you measure where possible is recommended, as this helps ensure accuracy. One person can focus on getting the measurements right while the other takes notes.

Here is your measuring kit checklist:

A spirit level is easy to overlook but worth having. If your decking or floor is not perfectly level, your balustrade height measurements will vary across the run. You need to account for that before you order.

Step 1: Draw a Simple Plan of Your Space

Before you take a single measurement, draw a rough plan of where your balustrade will go.

Always start with a rough drawing. This does not have to be a complex drawing, nor drawn to scale. By drawing out exactly where you want the system to sit, you can add measurements to a plan. This also helps identify where there may be some awkward spots in your design. 

Your plan should be a bird's eye view — looking down at the space from above. Draw the edges of your decking, patio, balcony, or staircase outline. Include any walls, doors, steps, or structural posts that are nearby.

Mark where you want the balustrade run to begin and end. Note any corners, changes in direction, or areas where the surface drops away. This plan becomes your reference throughout the whole measuring process. It also makes it much easier to communicate your project to a supplier when requesting a quote.

Step 2: Mark Your End Posts and Corner Posts

End posts are the posts at each end of a straight balustrade run. Corner posts sit at any point where the run changes direction by 90 degrees or more.

On your plan, mark the end posts and any corner posts at a 75mm distance from the edge. This distance is measured from the outer edge of your surface to the centre of the post. 

The 75mm rule is important. It stops post fixings from being too close to the edge of your substrate, which can cause the fixing to fail or crack the material. On concrete, timber decking, or stone patios, you need enough material between the post fixing and the edge to maintain structural integrity.

So if your balustrade is going along the edge of a decking area, your end and corner posts sit with their centres 75mm in from that edge. Mark this on your plan clearly.

Step 3: Space Your Mid Posts Correctly

Mid posts are the vertical posts that go between your end and corner posts. They support the glass panels along the run and must be evenly spaced.

Mid posts should be planned at intervals of between 1,000mm and 1,200mm apart. Consider the symmetry and aesthetic of the spacing as well as the structural requirement when calculating mid post positions. 

This means that for a 4,000mm run, you would typically place mid posts at roughly 1,000mm intervals, giving you four equal spans. For a 3,000mm run, you might space them at 1,000mm or 1,500mm depending on the glass thickness and system you are using.

Symmetry matters here. Unevenly spaced posts look wrong even when they are technically compliant. Try to divide your run so that all glass panels end up a similar width. A run of 3,600mm with three equal spans of 1,200mm looks much better than one of 1,000mm, one of 1,400mm, and one of 1,200mm.

Step 4: Calculate Your Glass Panel Widths

Once you have planned your post positions, you can calculate how wide each glass panel needs to be.

Glass panels are situated between the posts. You calculate panel width by measuring from the centre of one post to the centre of the next post, then deducting 90mm. The deduction accounts for a 21mm tube, 15mm for the glass clamp, and 9mm clearance on each side. This is doubled to account for both sides of the panel. 

So the formula for glass panel width is:

Centre-to-centre post distance minus 90mm = glass panel width

For example: if your posts are 1,200mm apart centre to centre, your glass panel should be ordered at 1,110mm wide.

Glass panels for balustrades are typically available in widths from 1,000mm to 1,200mm, with panels no wider than 1,100mm recommended for single-layer 10mm toughened glass. It is possible to go wider, with suppliers providing glass panels up to 3,000mm wide in some cases, but this is typically only suitable for thicker glass.

Always confirm maximum panel widths with your chosen supplier before finalising your post spacing. Wider panels may require a thicker glass specification.

Step 5: Measure the Height

Height is one of the most critical measurements. UK regulations set specific height requirements for glass balustrades: at least 1,100mm for balconies and external applications, and 900mm for indoor staircases and landings.

Here is how height is correctly measured depending on your system:

For post and handrail systems: Measure from the finished floor level up to the top of the handrail. This is your total barrier height.

For spigot systems without a handrail: Measure from the finished floor level to the top of the glass panel.

For channel systems: This is where people often go wrong. The height of a balustrade is measured from the finished floor level to the top of the handrail, or the top of the panel if there is no handrail. The minimum height does not take recessed parts into account for those installed via a floor channel. If you want a balustrade that reaches 1,100mm from floor level, your measurements should compensate for how high the panel will sit in the floor profile.

In simple terms, if your floor channel recesses 60mm below the surface, you need to order glass that is 60mm taller than your minimum required height to compensate.

Step 6: Measuring for Stairs

Staircase measurements are the most complex part of this process. Do not skip any of these steps.

Sketch a side-on view of the stairs ensuring you draw the correct number of steps. Measure the overall height, which is the distance from the floor or landing at the top of the stairs to the floor or landing at the bottom. Measure the overall horizontal length from the edge of the nosing on the first tread at the bottom to the edge of the nosing on the landing at the top. Measure the tread depth from front to back, and the riser height from the base tread to the tread of the next stair above it. These only need to be done for one step.

You also need to know the stair angle. You can measure this using a digital angle finder, a protractor, or an angle-finder app on your phone. Be aware that phone apps are not always fully accurate. For a made-to-measure glass order, a physical angle finder is more reliable.

If you are measuring up for glass on stairs, do not assume every step is exactly the same measurement. Measure each one individually. For very complicated stair installations or complex shaped glass, consider making a wooden template for the glass first.

On a staircase, the balustrade height is measured from the pitch line, not the tread surface. The pitch line runs along the front edge of each step. Your handrail must sit between 900mm and 1,000mm above this line at all points on the rake.

Step 7: Account for Corners and Returns

If your balustrade turns a corner, you need a corner post at the junction point. The same 75mm rule applies for corner post centres.

For internal corners (where the balustrade runs along two walls that meet), measure each run independently from the corner post centre outward. Do not measure across the corner as a single run.

For external corners (where the run projects outward at a corner of a terrace or balcony), mark your corner post centre at 75mm from each edge at the corner. From that corner post, measure your two runs in separate directions.

If your space has an unusual angle rather than a straight 90-degree corner, note the angle on your plan. Clearly note where each measurement is to and from, such as outside edge, centre line, overall length, and tube edge to tube edge. Small details really do make a difference in manufacturing.

Common Measurement Mistakes to Avoid

These are the errors we see most often, and the ones that lead to costly reorders.

Measuring total floor length without accounting for posts. The floor length is not the same as your glass panel width. Always calculate glass widths from post centre to post centre, minus the clearance deduction.

Forgetting to check if the surface is level. If your decking has a slight slope, your balustrade height will vary across the run. If your patio or surface has a slope or steps, measure the height at different points along the slope or step to ensure the balustrade will be level once installed. 

Measuring from the channel base instead of floor level. For channel systems, always measure from finished floor level to reach your required height above it. The glass needs to compensate for however deep it sits in the channel.

Not double-checking. Incorrect measurements can occur for several reasons including improper measuring tools, misreading the tape, and not double-checking. The result can be costly. Measurements too small create large gaps between panels, compromising safety and stability. Overly generous measurements mean panels will not fit together properly, and forcing them into place can cause glass to crack. 

Assuming all steps are the same on a staircase. Older staircases especially can have slight variations in riser height or tread depth. Measure each step individually to be safe.

Pro Tips From Experience

Send your plan to your supplier before you place the order. A reputable supplier will review your measurements and flag anything that looks incorrect before manufacture begins. At The Outdoor Look, we are happy to check your plan before you order from our glass balustrade range.

Use a laser measure for runs over 3 metres. A tape measure on a long run can bow slightly in the middle, giving you a reading that is a few millimetres too short or too long. On custom glass, even 5mm can matter.

Take photos of your space alongside your measurements. Photos help your supplier understand the fixing substrate, the surface material, and the surrounding conditions — all of which affect what components they recommend.

If your project involves a listed building or a roof terrace over a certain height, consult a structural engineer before finalising your measurements. Some installations require engineer-certified load calculations alongside the measurement plan. For detailed guidance on balustrade compliance requirements, you can review the full Approved Document K on the UK government planning portal at planningportal.co.uk.

Quick Reference: Measurement Checklist

Frequently Asked Questions

How do I calculate the width of glass panels for a glass balustrade? 

To calculate glass panel width, measure the distance between the centres of two adjacent posts. Then subtract 90mm from that figure. The 90mm deduction accounts for the post tube, glass clamps, and clearance on both sides of the panel. For example, if your posts are 1,200mm apart centre to centre, you order your glass panel at 1,110mm wide. Always confirm maximum panel widths with your supplier as this varies depending on glass thickness and system type.

Does the balustrade height measurement include the channel or fixing profile? 

No. In the UK, balustrade height is always measured from the finished floor level up to the top of the handrail or the top of the glass panel if there is no handrail. If your system uses a floor channel, the glass sits recessed inside that channel. You must add the channel recess depth to your glass height to ensure the visible barrier still reaches the required minimum height of 900mm for indoor use or 1,100mm for external balconies.

How far from the edge should I position balustrade posts? 

End posts and corner posts should be positioned with their centres 75mm from the outer edge of your surface. This applies to decking boards, concrete patios, stone terraces, and most other substrates. The 75mm distance ensures the post fixing has enough material around it to hold securely without risk of cracking or splitting the edge of the substrate.

Can I measure for a glass balustrade on my own, or do I need a professional? 

You can measure for a straightforward flat run on your own using a tape measure, spirit level, and a notepad. However, we recommend having a second person help you for runs over 3 metres, as holding a tape measure accurately over a long distance is difficult solo. For staircase installations, complex corners, or roof terraces, professional measurement or at least a supplier review of your plan is strongly advised. Custom glass cannot be resized after manufacture, so getting the measurements right before you order is essential.