There is no single standard window size, but common double-hung windows run 24 to 48 in wide and 36 to 72 in tall (61 to 122 cm × 91 to 183 cm). Sizes are written width first, in feet and inches: a 3040 window is 3 ft 0 in × 4 ft 0 in (36 × 48 in, 91 × 122 cm).
Window size chart
Each maker has its own size list, so every row below names its maker. Sizes are width × height in inches. Where the maker says whether the number is the rough opening or the window itself, the row says so too.
| Window type and maker | Size code: inches (W × H) | cm |
|---|---|---|
| Double-hung Pella | 2030: 24 × 362840: 32 × 482852: 32 × 62 | 61 × 9181 × 12281 × 157 |
| Double-hung Milgard Tuscany | 3040: 36 × 483060: 36 × 72(rough opening; window ½ in smaller) | 91 × 12291 × 183 |
| Double-hung Andersen 400 Series | TW2846:33 5/8 × 56 7/8(window frame) | 85 × 144 |
| Single-hung Pella | 2044: 24 × 52(same codes as double-hung) | 61 × 132 |
| Sliding Pella | 3020: 36 × 243030: 36 × 365030: 60 × 366040: 72 × 48 | 91 × 6191 × 91152 × 91183 × 122 |
| Sliding Milgard Tuscany | 4030: 48 × 365040: 60 × 48(rough opening) | 122 × 91152 × 122 |
| Casement Pella | 2436: 28 × 422640: 30 × 482850: 32 × 603060: 36 × 72 | 71 × 10776 × 12281 × 15291 × 183 |
| Picture Pella | 3020: 36 × 245030: 60 × 364050: 48 × 606040: 72 × 48 | 91 × 61152 × 91122 × 152183 × 122 |
| Awning Pella | 3020: 36 × 244024: 48 × 285030: 60 × 36 | 91 × 61122 × 71152 × 91 |
| Bay, 45 degree Andersen 400 Series | 46 7/8 to145 3/8 wide;14 3/16 to27½ deep | 119 to369 wide;36 to70 deep |
Sources: Pella standard window sizes; Milgard Tuscany double-hung and slider size tables; Andersen 400 Series double-hung and bay size tables, with the TW2846 size as listed at Home Depot.
Average window size
There is no official average, but the ranges agree. Milgard gives 24 to 48 in wide and 36 to 72 in tall (61 to 122 cm × 91 to 183 cm) as standard for double-hung kitchen windows, and Andersen builds its 400 Series double-hung from 21 5/8 to 45 5/8 in wide and 36 7/8 to 92 7/8 in tall (Milgard, Andersen). A typical bedroom or living room double-hung is about 3 ft wide and 4 to 5 ft tall, like Pella's 2840 and 2852 or Andersen's TW2846.
How window sizes are written
Window sizes are always width first, then height. Many makers shorten them to a four-digit code: the first two digits are the width in feet and inches, the last two the height. Milgard's example is 2846, a window 2 ft 8 in wide and 4 ft 6 in tall, which is 32 × 54 in (Milgard). Pella's is 2438: 2 ft 4 in × 3 ft 8 in, or 28 × 44 in (Pella).
So a 3040 window is 3 ft 0 in × 4 ft 0 in (36 × 48 in, 91 × 122 cm), and a 6040 slider is 6 ft × 4 ft (72 × 48 in).
Is the code the rough opening or the window?
It depends on the maker, and both Pella and Milgard warn you to check (Pella, Milgard). Three real examples:
- Milgard: the code is the rough opening. A Tuscany 3040 has a 36 × 48 in rough opening and a 35½ × 47½ in window.
- Andersen: the code is a model name, not a measurement. A 400 Series TW2846 measures 33 5/8 × 56 7/8 in (85 × 144 cm), frame to frame (Home Depot listing).
- Pella: its size guide lists codes and tells you to confirm whether a size refers to the opening or the exact window before you order.
Unit size vs rough opening
The unit size (also called the window, frame or net size) is the window itself, measured across the outside of its frame. Andersen puts it plainly: its window dimension "always refers to outside frame-to-frame dimension" (Andersen). The rough opening is the framed hole in the wall, between the studs and from the rough sill to the header.
The rough opening is always a little bigger, so the window can be shimmed level. Milgard windows are ½ in smaller than the opening in both directions (Milgard). Andersen's minimum rough opening for a 400 Series double-hung is ½ in wider than the window: a 2 ft 9 5/8 in window goes in a 2 ft 10 1/8 in opening. Andersen adds that the opening may need to be bigger still for building wrap, flashing, sill pans and fasteners (Andersen).
Common window sizes by type
Double-hung and single-hung
Both sashes slide in a double-hung window; only the bottom one moves in a single-hung. They share the same sizes. Pella lists 2030, 2044, 2840 and 2852 as common codes for both, from 24 × 36 in up to 32 × 62 in (Pella). Milgard's Tuscany double-hung comes in rough openings such as 3040, 3050 and 3060 (Milgard).
Sliding
Sliders are wider than they are tall. Pella's common sizes are 3020, 3030, 5030 and 6040 (Pella). Milgard's Tuscany slider runs from a 24 × 18 in to a 72 × 72 in rough opening (Milgard).
Casement
Casements are hinged on the side and crank out. They are usually taller than wide: Pella lists 2436, 2640, 2850 and 3060 (28 × 42 in to 36 × 72 in). For kitchens, Milgard gives 14 to 35½ in wide and 17 to 73 in tall (Milgard).
Picture
Picture windows do not open, so they can be large. Pella's common sizes are 3020, 5030, 4050 and 6040, up to 72 × 48 in (183 × 122 cm).
Awning
Awning windows are hinged at the top and open outward, and are usually wide and short. Pella lists 3020, 4024 and 5030.
Bay and bow
A bay is three windows set at an angle so they project from the wall. Pella says the center window is often about half the total width and the two sides about a quarter each, set at 30 or 45 degrees (Pella). Andersen's 400 Series 45 degree casement bays run 3 ft 10 7/8 in to 12 ft 1 3/8 in wide and project 14 3/16 to 27½ in (Andersen). A bow uses four or more equal windows in a curve.
Bedroom egress minimums
A bedroom window has to be big enough to climb out of. The International Residential Code, Section R310.2, sets four numbers for this emergency escape and rescue opening (Boulder County, 2021 IRC, St. Paul, Minnesota Residential Code):
All four apply to the open hole, not the window size. A 20 × 24 in opening meets both minimums but is only 3.3 sq ft, so at least one side has to be bigger. Pella, Andersen and Milgard all print the 5.7 sq ft, 20 in and 24 in minimums with their size charts (Pella, Andersen, Milgard).
A double-hung window only opens about half its height, so it has to be tall. Here is how common sizes do, using the makers' own clear-opening figures:
| Window | Clear opening, in (cm) | Area, sq ft (m²) and egress |
|---|---|---|
| Milgard double-hung 3050 | 31¼ × 22(79 × 56) | 4.77 (0.44)Fails: too short |
| Milgard double-hung 3060 | 31¼ × 28(79 × 71) | 6.08 (0.56)Passes |
| Andersen TW2846 | 29 7/8 × 24¼(76 × 62) | 5.05 (0.47)Fails: area |
| Andersen TW3046 | 33 7/8 × 24¼(86 × 62) | 5.72 (0.53)Passes, just |
| Andersen TW2852 | 29 7/8 × 27¾(76 × 70) | 5.77 (0.54)Passes |
| Milgard slider 4030 | 21 3/16 × 32½(54 × 83) | 4.78 (0.44)Fails: area |
| Milgard slider 5030 | 27 3/16 × 32½(69 × 83) | 6.14 (0.57)Passes |
Clear openings from the Milgard Tuscany double-hung and slider tables and the Andersen 400 Series area and opening specifications.
Check your local code. Cities and states adopt the IRC with changes, and the subsection numbers move between editions (in the 2021 IRC they are R310.2.1 to R310.2.3). Basement windows below grade also need a window well. Confirm the rules with your building department, and see egress window size for wells, ladders and casement sizes.
Window height from the floor
Window heads usually line up with the door heads. Andersen's tables assume a structural header at 6 ft 10½ in (82½ in, 210 cm), the same height as the common 82½ in rough opening for an exterior door (Andersen, Masonite). With that header, an Andersen TW2846 has its inside sill 29 5/32 in (74 cm) above the subfloor, and a taller TW3052 sits at 21 5/32 in (54 cm).
In a bedroom, Pella advises keeping the sill no higher than 44 in and no lower than 24 in above the floor (Pella). More on sill heights by room: window height from floor.
How to measure for a replacement window
A replacement window fits inside the existing frame, so you measure that frame, not the wall. These steps follow Milgard's guide (Milgard).
- Width. Measure from inside jamb to inside jamb at the top, middle and bottom of the window. Keep the smallest number.
- Height. Measure from the sill to the head at the left side, the center and the right side. Keep the smallest number.
- Square. Measure both diagonals. If they are within ¼ in of each other, a standard replacement window will fit. If not, plan on a new frame or a new-construction window.
- Depth. Check there is at least 3¼ in of depth from the front to the back of the trim for the new window to sit in.
- Round down. Some installers round each measurement down to the nearest 1/8 in. Give the maker your smallest width and height, and let them size the window to it.
For a new-construction window, size from the rough opening instead: Andersen and Milgard both print the rough opening next to every size.
Questions people ask
What does 3040 mean on a window?
3 ft 0 in wide by 4 ft 0 in tall, which is 36 × 48 in (91 × 122 cm). Width always comes first. Check whether the maker means the window or the rough opening.
What is the most common window size?
For double-hung windows, about 3 ft wide and 4 to 5 ft tall. Pella's common codes include 2840 and 2852, and Andersen's TW2846 is 33 5/8 × 56 7/8 in.
Is the window size the rough opening?
Sometimes. Milgard's codes are the rough opening, with the window ½ in smaller. Andersen's model numbers are names, and the real frame size is listed separately.
What size window do I need for a bedroom?
One that opens to at least 5.7 sq ft, 24 in high and 20 in wide, with the sill no more than 44 in off the floor. A Milgard 3060 double-hung or a 5030 slider meets it; a 3050 double-hung does not.
What size is a standard bathroom window?
Milgard puts standard bathroom windows at 24 to 36 in wide and 36 to 72 in tall (61 to 91 × 91 to 183 cm). Pella notes a bathroom can skip the window if it has an exhaust fan.
Can I put a bigger window in the same opening?
Not without reframing. The rough opening sets the largest window that fits; a bigger one needs a new header and studs, and usually a permit.
Sources
- International Residential Code, Section R310.2, as summarized by Boulder County, B10 emergency escape and rescue openings (2021 IRC) and City of St. Paul, egress window handout (2020 Minnesota Residential Code)
- Andersen, 400 Series Tilt-Wash double-hung size table, 400 Series Tilt-Wash area and opening specifications, 400 Series casement bay and bow size table
- Pella, standard window sizes
- Milgard, understanding standard window sizes, Tuscany double-hung clear opening and egress table, Tuscany horizontal slider clear opening and egress table, how to measure for replacement windows
- Masonite, how to measure for exterior doors (door rough opening heights)
- The Home Depot, Andersen 400 Series TW2846 product listing
Checked October 7, 2026. Metric values are converted from inches and rounded to the nearest cm; areas are converted from square feet.