Standard window dimensions: common sizes and when you need made-to-measure

“What are the standard dimensions for windows?” is one of the questions we get asked most often before a quote. The honest answer is an uncomfortable one: a true standard, fixed like a formal norm, doesn’t exist. In Italy, every opening is slightly different from the next, even within the same house, and this completely changes how you should think about sizes.

There are, however, recurring sizes — dimensions that come up often because of how buildings and wall openings are typically constructed. Knowing them helps you form an idea before calling a window installer. In this article you’ll find the most common sizes for single- and double-sash windows and for French doors, how an opening is actually measured, why made-to-measure is the rule rather than a luxury, and how size, number of sashes and weight relate to one another. Important premise: every measurement you read is indicative and given as an example, orders of magnitude among the most common, not universal regulatory values.

Why a true “standard” for windows doesn’t exist

When it comes to furniture, appliances or internal doors, a standard makes sense: a built-in fridge or an internal door follows precise modular dimensions because the industry has fixed them. Windows are different, and the reason is simple: a window isn’t simply placed in position, it’s fitted into a hole in the wall, and that hole is a piece of masonry work, not an industrial product.

Two flats built by the same company in the same year can have window openings that differ by a few centimetres because of the plaster, the reveal, or how the sub-frame was built. In older buildings the variability is even greater: it’s not unusual to find the same “model” of window with different dimensions from room to room. This is why a properly made window is always built to the actual size of your opening, surveyed on site, rather than picked off a shelf of ready-made pieces.

The “standard sizes” you find around are therefore a starting map, useful for orientation and for understanding which bracket you fall into, not a catalogue to order from. If you want a general picture of how a window is made and chosen, start with the complete guide to PVC windows, which sets out the basic concepts without unnecessary technicalities.

Recurring sizes for single-sash windows

The single-sash window is the most common for kitchens, bathrooms, single bedrooms and utility rooms. The recurring widths sit indicatively between 50 and 80 cm: beyond this width, for reasons of weight and ease of opening, it’s common to move to two sashes.

The table below shows indicative dimensions among the most common, expressed as width x height. To repeat: these are orders of magnitude, not legal measurements, and standard sizes vary from building to building.

Indicative size (W x H cm)	Typical use	Notes
50 x 70	Bathroom, utility room	Among the smallest; often top-hung
60 x 100	Kitchen, bathroom	Very common “small” window
60 x 120	Bedroom, kitchen	Recurring single-sash size
80 x 120	Bedroom, living room	Comfortable upper limit for a single sash
80 x 140	Bedroom	Tall sash; weight should be assessed

These values are given as an example. The rule of thumb is that beyond a certain width a single sash becomes heavy and cumbersome to open, at which point it’s worth splitting the opening into two.

Recurring sizes for double-sash windows

The double-sash window is the typical “living room” or double-bedroom window, with the central mullion (fixed or with a moving joint). It’s used when the width exceeds roughly 90-100 cm. Recurring widths run indicatively from 100 to 150 cm.

Indicative size (W x H cm)	Typical use	Notes
100 x 120	Bedroom, living room	Small “double”, very common
120 x 120	Living room	Among the most requested overall
120 x 140	Living room, bedroom	Recurring double-sash size
140 x 140	Large living room	Large double-sash window
150 x 150	Living room, large spaces	Towards the practical limit for two sashes

Again, these sizes are indicative. Above certain dimensions, or to let in more light, different solutions are worth considering (three sashes, or sliding systems). If your opening is large and faces onto a usable outdoor space, it’s worth reading the guide to sliding and lift-and-slide windows, because there the logic of sizing changes completely.

French doors: typical sizes

The French door (or “full-height window”) is walked through, so its height matches that of a passageway: indicatively around 220-240 cm high, with width varying according to the number of sashes.

Indicative size (W x H cm)	Sashes	Typical use
80 x 230	1 sash	Secondary access, narrow balcony
90 x 230	1 sash	Single balcony
120 x 230	2 sashes	Balcony, terrace
140 x 240	2 sashes	Living room onto terrace

These are orders of magnitude: the height depends on the finished floor level and the threshold, which vary from house to house. On a French door the weight of the sash becomes a serious factor, which we cover further on.

How the opening is measured: the three concepts that matter

This is the heart of the matter, and the reason “standard sizes” on their own aren’t enough. When you measure a window opening, there isn’t a single measurement — there are several, and confusing them is the most common mistake. This section is informative, to help you understand what the technician will ask you — it is not a guide to surveying or installation: those are done on site, with the right tools.

• Rough wall opening (architectural opening). This is the size of the raw hole in the wall, from reveal to reveal and from threshold to lintel. It’s the “gross” size of the hole.
• Window opening / sub-frame opening. This is the actual space the window will go into, accounting for any sub-frame (the fixed frame embedded in the masonry to which the window is fixed).
• Clear opening. This is what’s actually left free with the window open — that is, the usable opening net of the frame. It’s always smaller than the rough wall opening.

Term	What it indicates	What it’s used for
Rough wall opening (architectural)	Raw hole from reveal to reveal	Starting point of the survey
Window opening / sub-frame	Actual space for the window	Sizes the window
Clear opening	Free opening net of the frame	Understanding actual light and air

The difference between these figures isn’t a minor detail: between the rough wall opening and the finished window there can be several centimetres of variance, depending on the type of installation and sub-frame. This is why a badly taken measurement throws off the entire window, and it’s why anyone who does the job properly comes to measure in person. What to check before signing, you’ll find in our checklist on what to check in a quote.

Tolerances: why a few millimetres matter

A window doesn’t slot perfectly into the opening. Between the frame and the masonry an installation joint is needed, a gap of a few millimetres that is later sealed and insulated. This joint serves two purposes: allowing correct fixing and insulation, and absorbing the tolerances of the wall (which is never perfectly square).

In other words: the window is always built slightly smaller than the rough wall opening, by an amount that depends on the installation method chosen. This is also why catalogue sizes shouldn’t be taken literally: they need to be checked against the actual opening and the type of installation. It’s the technician, during the survey, who calculates the manufacturing size starting from the rough wall opening.

Why made-to-measure is the norm, not a luxury surcharge

There’s a widespread, mistaken idea that “made-to-measure” automatically means “more expensive” or “a luxury item”. In quality windows and doors it’s exactly the opposite: made-to-measure is the normal way of working. A properly made window is practically always built to the size of your opening, because that’s the only way to guarantee its tightness, insulation and durability.

“Standard-sized” windows kept ready in stock do exist, but they’re an exception for specific cases (quick replacements, mass-market housing, very tight budgets), and they come with a trade-off: either you adapt the opening to the window with masonry work, or you accept wider joints and a less clean installation. Building a window to your own measurements isn’t a premium whim — it’s simply the correct way to make one. This is why, when you compare quotes, the fact that they’re “made-to-measure” isn’t some odd extra cost: it’s simply how a properly made window is done. You’ll find our PVC windows and the full range on the windows and doors page.

Size, number of sashes and weight: the link that’s often overlooked

There’s a direct relationship between how large a window is and how it needs to be built: this is where dimension stops being an aesthetic number and becomes a technical fact. The larger a window, the heavier the glass; the heavier the glass, the more it matters how the sash and hardware are sized.

Glass is the heaviest part of a window: a double-glazed unit weighs indicatively around 20-25 kg/m², a triple-glazed unit even more. A single very wide sash can therefore become awkward to operate and put strain on the hardware over time. This is why, beyond a certain width, windows move to two sashes: not for looks, but to distribute the weight across two more manageable elements.

Sash size (indicative)	Practical effect	Typical choice
Width up to ~80 cm	Light, comfortable sash	1 sash
Width ~90-150 cm	High weight on a single sash	Often 2 sashes
Large panoramic openings	Significant weight and bulk	Sliding / lift-and-slide

Triple glazing also factors into this: it adds performance but weighs more, and on large sashes it requires suitable hardware. In short, size is never an isolated choice — it brings with it the number of sashes, the type of opening, and the hardware.

When it’s NOT a good idea to think in “standard sizes”

Recurring sizes are useful for orientation, but there are situations where relying on the standard is a mistake. Here’s when to stop and think it through properly.

• When you already have the opening and want an accurate quote. If you’re replacing existing windows, standard sizes aren’t of any use: you need a survey of your actual opening. Relying on a “catalogue” size can lead you to compare quotes on the wrong basis.
• When the building is old or irregular. In older houses, openings are often out of square and different from one another. There, the “standard” is nearly useless: every window is its own case and must be measured individually.
• When you’re chasing a low price by forcing a ready-made size. Buying a standard-size window “because it costs less” and then having to adapt it to the opening with masonry work can wipe out the initial saving, and often makes the installation quality worse.
• When the size calls for a different type of window. If the opening is very large, insisting on a “standard” side-hung window doesn’t make sense; at that point the conversation moves to sliding or lift-and-slide systems, with a different sizing logic.

In all these cases, the point isn’t to find the “right” catalogue size, but to have the opening surveyed by whoever will actually build the window.

FAQ

Is there an official standard size for windows in Italy? No. There’s no regulation that fixes universal dimensions: the product standard EN 14351-1 covers performance and CE marking, not dimensions. There are only recurring sizes that come up often, but every opening must be measured individually.

What are the most common sizes for a double-sash window? As an example, the most frequent sizes are around 120x120 and 120x140 cm, with indicative widths between 100 and 150 cm. These are orders of magnitude, not fixed measurements: standard sizes vary from building to building.

What’s the difference between the rough wall opening and the window opening? The rough wall opening (or architectural opening) is the raw hole from reveal to reveal; the window opening is the actual space the window will go into, accounting for the sub-frame. There can be several centimetres of difference between the two depending on the installation.

Can I take the measurements myself and order the window? It’s risky: you need to distinguish between the rough wall opening, the sub-frame and installation tolerances, and an error of a few millimetres compromises the entire window. This is why anyone working properly surveys the measurements in person before building.

Does a made-to-measure window cost more than a standard one? In quality windows, made-to-measure is the norm, not a luxury extra: the window is built to your opening because that’s the only way to guarantee tightness and insulation. Price differences depend on the profile, glass and hardware, not on whether it’s “made-to-measure”. You’ll find the ranges in our guide to PVC window prices.

Why does a window move to two sashes beyond a certain width? It’s a matter of weight. Glass is heavy (indicatively 20-25 kg/m² for double glazing), and a sash that’s too wide becomes awkward and puts strain on the hardware. Splitting into two sashes distributes the weight and makes the opening more comfortable.

In summary

Windows don’t have standard sizes in the strict sense: they have recurring sizes, useful for orientation but never to be taken literally, because every opening is different and must be measured on site. Understanding the difference between the rough wall opening, the window opening and installation tolerances also explains why made-to-measure isn’t a luxury, but the correct way to build a window. And dimension always brings with it the number of sashes, weight and type of opening: it’s never a purely aesthetic choice.

Want to know the actual size and real price for your windows, not a catalogue range? Send us your requirements and we’ll come and survey the openings: request a quote and get a proposal built around your own measurements, with CE-certified German Salamander profiles and management entirely handled in Italy.