Why Should You Know How to Measure for Double Glazing Sizes?

If you want new double glazing, knowing your double glazing sizes is very important. If you have an installer, he will send a technical surveyor. However, if you plan to install it yourself, you need to be doubly sure of your double glazing sizes. If you don’t, you may face delays. What’s more, you might even lose money.

The correct measurement of double glazing sizes is essential for home improvement projects

How, you ask?

It’s simple. Let’s say you measure your double glazing. However, your measurements aren’t accurate. Maybe you measured the visible fitting instead of measuring the actual aperture. Maybe you failed to take the 10mm fitting allowance into account. Whatever it was, somehow, your measurements are off.

When you place your order, you will use these inaccurate measurements. When your double glazing arrives, it will not fit your apertures. Now, you can’t return them and get a refund. You will lose the money you spent. Moreover, you will need to place another order with the correct double glazing sizes.

Since double glazing may take anywhere from 14 days to 21 days to be manufactured, you also lose all that time.

As you can see, getting accurate measurements is quite important. However, how do you actually take proper measurements? Let’s find out…

What Should You Keep in Mind When You Measure for Double Glazing Sizes?

Measuring your double glazing is a simple matter if you keep certain points in mind. Your double glazing sizes don’t mean the size of the fitting. In fact, you need to measure your opening, or aperture. This is a common mistake people make. Additionally, to get an accurate figure, you can’t rely on one set of measurements. Let’s see what you need to keep in mind when measuring your doors and windows.

Always Measure from Outside

This is an easy point to forget, but is very important. It is essential to remember that your double glazing is fitted from the outside. Therefore, if there is a difference in measurement between the inner and outer aperture, it can be a problem.


Because if your inner aperture is slightly wider than your outer aperture, your double glazing won’t fit. Alternatively, your double glazing might be too small and not fit properly. This is why you should always measure double glazing sizes from the outside.

The only exception to this rule is measuring bay and bow windows. You need to take both inner and outer measurements for them.

Bay and bow windows require inside and outside measurements for proper double glazing sizes

Measure Brick-to-Brick

Again, the double glazing sizes are not measured on the fitting themselves. They are, in fact, the measurement of the aperture. This is why it is important that you measure from brick to brick, and not just the visible frame.

Your double glazing is manufactured according to the size of the aperture. The width of the frame can vary according to the material. For example, a uPVC frame will be thicker than hardwood or aluminium frames.

If you measure the width of the sash or the panel, you won’t take into account the width of the frame itself. As a result, if your old windows are a different material from what you are ordering, you will have improper double glazing sizes.

Take 3 Sets of Measurements

The measurement of any opening in a house is not absolutely precise. There can be variations, albeit minor, at various points in the aperture. It could be as minor as a few millimetres, or as drastic as an imperceptible increase or decrease along the length or width. To counteract discrepancies caused by this, you should always take at least 3 sets of measurements.

If you are measuring the length, take the left edge, right edge, and centre for your double glazing sizes. For the width, measure along the top, bottom, and centre. This give you a more or less precise assessment of the aperture’s width. Finally, just take out the average of the three figures to get your final measurement. To do that, simply add the 3 figures, and divide the sum by 3.

Additionally, remember to subtract 10mm from the final double glazing sizes. This is for fitting allowance, which is 5mm on either side.

Measure Inclusions as Well

In addition to the double glazing sizes, you need to measure the inclusions as well. This includes the width of the cill, and any frame extenders or additional fittings. If possible, measure the width of the sealed double glazed unit as well. You may even break this down into the width of the panes of glass and the space between them.

For example, a 20mm unit will have 2 panes of 4mm glass separated by a 12mm gap.

You will need these double glazing sizes when you order your sealed double glazed unit. If you have measured the glass from edge to edge, specify in your order that these are ‘tight’ measurements. This way, the company will know to deduce the fitting allowance. The more detailed you are, the more accurate your double glazing sizes will be.

What Should You Do If You Aren’t Sure of Your Double Glazing Sizes?

Double glazing installation companies will measure double glazing sizes before ordering

Measuring your double glazing sizes may not be rocket science. However, if it’s your first time, you may understandably be nervous. Even minor mistakes in measuring your double glazing sizes might mean a wasted unit. This is why, if you aren’t sure, get some expert advice.

One way of doing it is to get your installation company to come and do a full technical survey. They will send in an expert surveyor who will not only measure your double glazing sizes, but also assess your double glazing needs for Building Regulations compliance.

However, it might be that you aren’t hiring a double glazing installation company. You may have your own carpenter or glazier who will install your double glazing. Alternatively, you may want to do it yourself, like we mentioned earlier.

If you are hiring a trusted local carpenter, you could ask him to come and measure your double glazing sizes. He will be experienced at this. Not only will you get accurate measurements, but also tips on how to do it yourself the next time.

Alternatively, if you want to try your hand at installing your fittings yourself, you can pay a carpenter to measure your double glazing sizes. Alternatively, you can contact us. Leave us a message online and we shall get back to you. Our expert staff is highly knowledgeable about all aspects of double glazing sizes. They will talk you through the process. Moreover, they will also recommend trusted local installers if you need them.

Frequently Asked Double Glazing Questions

Frequently Asked Double Glazing Questions

Should I replace my old sash windows?

Sash windows are a key feature for many traditional period buildings. Sash windows were traditionally built using timber, which is fairly high maintenance and has a tendency toward rotting and warping. Over time, these windows can become draughty and insecure. uPVC sash windows are a great way to experience the benefits of modern double glazing, without sacrificing the aesthetic of your home. uPVC sash windows will not rot or warp and require little maintenance. They are also thermally efficient, which means that your home will not require as much heating.

How much does it cost to double glaze a 3 bed house?

On average a double glazed window will cost between £350 and £400, with a uPVC door typically costing £600. This means that double glazing a 3 bedroom semi can cost between £3500 and £5000.

How much does it cost to install a window?

The prices given in our pricing tables, our online quotes and our costing calculators reflect the price of the window itself as well as the cost of installation. For example, a 500mm x 500mm casement window will cost between £150 and £175 including the cost of installation.

Is Double Glazing Easy to Break?

No, double glazing is not easy to break which means your home will be more secure. When attempting to smash double glazing often what happens is that the first pane of glass and the second will remain intact. This is due to the argon gas working as a shock absorber. This will mean the smash is very loud but unsuccessful on the first attempt.

Is Double Glazing Worth It?

Double glazing helps make your home more energy efficient as it prevents the loss of heat. During the summer, it helps to keep the heat out of your home. It provides your home with sound insulation which is perfect for houses that are in busy areas and streets. Double glazing also makes your home safer and more secure.

How Long Does Double Glazing Last?

It is important to note that the argon gas that separates the panes of gas, giving double glazing its energy efficiency will eventually leak out overtime. Double glazing has an average life span of about 20 years, however, this can vary depending on materials used and the installation.

How Do I Know If My Double Glazing Needs Replaced?

Double glazing will need replaced after a while due to the nature of the design – the gas that separates the two window panes slowly leaks out over time meaning the energy efficiency of your window is compromised. If your double glazing allows cold spots; water to seep through the frame; has cracks or chips in the window or has a build-up of condensation between the two panes of glass (misted windows), you should probably look into getting your double glazing replaced or repaired.

Should I Double Glaze My Windows?

Double glazing works to make your house more energy efficient saving you money on your heating bills. Double glazing also provides sound insulation which is perfect if your house is situated near busy roads and noisy areas. Double glazed windows are also tougher and harder to break than single glazing windows making your house more safe and secure.

What Can Cause Double Glazing To Crack?

Double glazing can crack for what appears to be no particular reason at all. A sealed window unit faces constant pressure either side of the glass, however, most of the time double glazing is strong enough to deal with this. Winter can be one of the worst time for cracked glass as the difference of temperature on either side of the glass stressing it to the point it can crack.

Is uPVC Flammable?

No, uPVC isn’t flammable and is actually a fire retardant.

How Do I Know If My Double Glazing Needs Repaired?

There are four tell-tale signs that your double glazed windows need repair or replaced: There are chips and cracks in the panes of glass; there is condensation (misted windows) between the two panes of glass; the window allows cold air through; water begins to seep through the frame. If your double glazing does any of these things, you may need to get your double glazing repaired or replaced.

Does Double Glazing Block Sound?

Double Glazing not only provides heat insulation but it also provides sound insulation too. Double glazing is perfect for houses in busy areas and streets.

What Does Double Glazing Do?

Double glazing makes your house more energy efficient, keeping heating in and keeping the cold out during winter months. During summer months, it helps keep the hot air out, keeping your house cooler. It also works to insulate sounds from busy areas and roads, leaving your house more peaceful and quieter.

Is double glazing easy to break?

Double glazing is a strong option for windows compared to single glazing. The frames are durable and there are high security locking options. As double glazing is made from glass it is possible to break however you will have to exert quite a bit of force to do this. This is practically impossible to do without making a noise.

Is double glazing expensive?

Double glazing can be an affordable addition for many homeowners. The price you pay can depend on the quality of the windows and the energy ratings. Other factors are the style of the windows, the colour of the frames and the type of glass. Why not get an online double glazing quote to get an idea of the price.

What is the average cost to double glaze a house?

The average cost to double glaze a house will depend on the size of your house and the number of windows. To double glaze a flat or apartment it will probably cost around £2,000. The average cost to double glaze a house is usually between £4,500 to £7,500. If you collect a number of double glazing quotes you will be able to compare companies and prices.

How much is double glazing per window?

Double glazing prices per window can vary from around £150 to £600 depending on the specification. The window style, type of glass, frame colour and handles are all contributing factors. To find out the true double glazing price per window it is a good idea to get a number of quotes to compare.

If I Use Double Glazing on the Web Who Will Fit My Double Glazing?

Double Glazing on the Web have a fully accredited network of local installers. Once you have created your free online quote we will put you in touch with up to three reputable local suppliers. Each of these suppliers will offer you a free no obligation quote and who you choose is completely up to you.

Are Double Glazed Windows Good For The Environment?

Once of the best ways of making your home more energy efficient is insulation. Double glazed windows act as another layer of insulation, helping to prevent the loss of valuable heat.

Instant Double Glazing Prices