Standard Window Sizes: Dimensions for Every Window Type

Most size charts list windows as a four-digit number, and once you can read it the whole chart opens up. The first two digits are the width and the last two are the height, each given in feet and inches. So a 2020 window is 2 feet 0 inches by 2 feet 0 inches, or 24 by 24 inches, and a 3050 window is 3 feet 0 inches wide by 5 feet 0 inches tall, or 36 by 60 inches.

There is one catch that trips people up: the code is the nominal, or call, size, not the exact measurement. The actual window is built about a half inch smaller in each direction so it has room to fit and shim square in the opening. That clearance is normal and expected, so do not panic when a 3050 unit measures slightly under 36 by 60.

Keep the difference between nominal and actual in mind as you read the sizes below. The numbers name the size you order, while the real glass-and-frame unit is a touch smaller by design.

Each window style has its own range of stock sizes, shaped by how it operates and where it usually goes. The lists below cover the everyday sizes you will find at most suppliers, given as width by height in inches. Treat them as the common band rather than a hard limit, since brands extend a little past these at the edges.

If you are still deciding which style fits a room, our guide to the types of windows explains how each one operates before you worry about dimensions.

• Double-hung: the most common style, roughly 24 to 48 in wide and 36 to 72 in tall. Frequent call sizes include 2436, 2840, 3046, and 3050. See our double-hung window page.
• Casement: narrower, about 14 to 36 in wide and 29 to 78 in tall, since a single crank-out sash spans only so far. Details on the casement window page.
• Sliding: wide and short, about 36 to 84 in wide and 24 to 60 in tall, made for low, broad openings.
• Picture: the widest range, from roughly 24 by 12 in up to 96 by 96 in, since a fixed pane has no moving parts to limit it.
• Awning: usually wider than tall, commonly 24 to 60 in wide and 20 to 42 in tall, often set above or below other windows.
• Bay and bow: assembled from several units, so they span far wider, often 3.5 to 10-plus feet across the full projection.

A handful of sizes dominate real homes. The 2840, 3040, and 3050 double-hungs turn up constantly in bedrooms and living rooms, while wide sliders and picture windows anchor great rooms and kitchens. It is completely normal for one house to mix several sizes and styles, and matching new units to the existing openings almost always looks better than forcing every window to a single dimension.

Before you match an opening to a stock size, you have to measure it correctly, and the trick is that openings are rarely perfectly square. Measure the width in three places, at the top, middle, and bottom of the opening, and write down the smallest of the three. Do the same for height on the left, center, and right, again keeping the smallest number.

Those smallest figures are your working dimensions, because a window has to clear the tightest point of the opening to go in at all. From there, a replacement unit is ordered slightly under the opening so it can be shimmed level and plumb.

Two habits cause most reordering. The first is measuring the old window or its glass instead of the opening itself, which gives a number that comes out too small. The second is taking a single measurement and trusting it, when a settled older opening can sit a half inch out of square from top to bottom. Measure the opening, in three spots, every time.

1. Measure width at the top, middle, and bottom; keep the smallest.
2. Measure height at the left, center, and right; keep the smallest.
3. Check for square by comparing the numbers; readings within about a quarter inch usually take a standard window.
4. Subtract the clearance the manufacturer specifies so the unit fits and shims square.

One distinction saves a lot of confusion: the rough opening is not the same as the window size. The rough opening is the framed hole in the wall, measured to the studs, and it is intentionally larger than the window so there is room for the frame, shims, and a bead of insulation around it. The window size is the unit itself, which sits inside that opening.

As a rule of thumb, the rough opening is about an inch wider and an inch taller than the actual window, though you should always follow the manufacturer’s exact figures. Getting these two numbers mixed up is how people end up ordering a window an inch too big or too small.

For a straight replacement, you are usually working to the existing frame and the smallest opening measurement, not the rough opening. For new construction or a resized opening, the rough opening is what the framer builds to, and the window is chosen to suit it.

Not every size is a free choice, because safety codes set a floor for rooms people sleep in. Bedrooms and finished basements need at least one window that opens wide enough to climb out of in a fire, and the rule covers the clear opening, not the call size. That clear opening is what is left once the sash is fully open, which is smaller than the window itself.

On a lot of older homes around Columbus, the original openings predate today’s standard sizes, so a true stock window rarely drops straight in. We usually either build the opening to a stock size or order the unit to the exact measured dimensions.

The widely used minimums are a clear opening of about 5.7 square feet, with a minimum clear height around 24 inches, a minimum clear width around 20 inches, and a sill no higher than 44 inches off the floor. Because a casement opens fully and a double-hung only opens halfway, the two can need very different overall sizes to hit the same clear opening, which is worth checking before you settle on a bedroom window.

Standard sizes cover most of the market, but plenty of homes fall outside them, and central Ohio has more than its share. Older Columbus housing stock was built before today’s stock dimensions, and decades of settling leave openings out of square, so a catalog window often will not seat cleanly without help. That is not a problem, just a fork in the road.

You generally have two options when an opening is non-standard. You can have the opening adjusted, adding or furring the framing so a stock window fits, which keeps the window cost down. Or you can order a custom-sized unit built to the opening, which costs more for the window but avoids carpentry on the wall.

Which way makes sense depends on how far off the opening is and the condition of the existing frame. A small mismatch is usually cheaper to shim or fur; a badly out-of-square or rotted opening is often better fixed before any window goes in. A measured assessment settles it quickly rather than guessing from a tape alone.