How Window Sizing Works
Window sizes are written width-first, in feet-and-inches shorthand. A "3050" window is 3 feet 0 inches wide and 5 feet 0 inches tall. The nominal size describes the rough opening the window is designed for; the actual unit measures about half an inch less in each direction so installers can shim it plumb and square.
That half inch is why measuring for replacement windows is a professional's job — measure the frame instead of the opening (or vice versa) and you've bought a window that doesn't fit. When Wood Windows quotes a Treasure Valley home, we measure every opening three ways: width at top, middle, and bottom; height at left, center, and right; then the diagonals to check square. Houses settle; 40-year-old openings are rarely rectangles.
Standard Double-Hung Window Sizes
Double-hungs are the most common window in American homes. Standard widths run 24 to 48 inches, heights 36 to 72 inches.
| Nominal size | Width × Height | Typical use |
|---|---|---|
| 2030 | 2'0" × 3'0" | Bathrooms, hallways |
| 2440 | 2'4" × 4'0" | Kitchens, secondary bedrooms |
| 2850 | 2'8" × 5'0" | Bedrooms, living areas |
| 3050 | 3'0" × 5'0" | Bedrooms (egress-friendly), living rooms |
| 3460 | 3'4" × 6'0" | Living and dining rooms |
| 4060 | 4'0" × 6'0" | Large living spaces |
Standard Casement Window Sizes
Casements crank outward and seal tighter than double-hungs (they test at better air-infiltration and U-factor numbers). Standard widths run 1'2" to 3'0" per sash; heights 2'6" to 6'0".
| Nominal size | Width × Height | Notes |
|---|---|---|
| 1830 | 1'8" × 3'0" | Kitchens, over counters |
| 2040 | 2'0" × 4'0" | Bedrooms, offices |
| 2450 | 2'4" × 5'0" | Bedrooms — check egress clear opening |
| 2850 | 2'8" × 5'0" | Living areas, easily meets egress |
| 3060 | 3'0" × 6'0" | Great rooms, stairwells |
Standard Picture & Sliding Window Sizes
Fixed picture windows go bigger because there's no operating hardware: common sizes run from 2'0"×3'0" up to 8'0"×5'0" and beyond. Horizontal sliders — everywhere in 1970s–2000s Treasure Valley construction — commonly come in 3'0", 4'0", 5'0", and 6'0" widths with 2'0" to 5'0" heights.
| Type | Common range | Where you'll see them |
|---|---|---|
| Picture (fixed) | 24"–96" wide × 12"–96" tall | Living rooms, view walls, gables |
| Horizontal slider | 36"–84" wide × 24"–60" tall | Bedrooms, basements, ranch homes |
| Awning | 24"–48" wide × 20"–36" tall | Above/below fixed glass, bathrooms |
Egress Sizes: The Code That Overrides Everything
Every sleeping room needs at least one window (or door) big enough to escape through. Idaho jurisdictions follow the IRC: 5.7 square feet of clear opening (5.0 for ground-floor windows in some cases), at least 20 inches wide, at least 24 inches tall, sill no higher than 44 inches off the floor.
The trap: those are clear opening numbers — the hole you can actually climb through when the window is open — not the window's nominal size. A 3050 double-hung only opens half its height. This is the single most common code issue we catch when quoting basement finishes and bedroom remodels in Boise and Meridian, and it's an easy one to get right at ordering time.
When Standard Sizes Aren't the Answer
Replacement work rarely uses stock sizes anyway. Manufacturers build each window to the measured opening, so "standard sizes" matter most for new construction and additions, where framing to a stock size can save money. For replacements in older Boise homes — where a 1948 opening might be 31¼" × 57⅝" — made-to-measure is the normal path and adds surprisingly little cost.
If you're planning a project, our team measures free of charge anywhere in the Treasure Valley. Call (208) 376-2200 or use the form on this page.
Frequently Asked Questions
What is the most common window size?
For double-hung windows in American homes, 28×54 inches and 32×54 inches are among the most common. Builders order in 2-inch width increments, so you'll see a lot of 24, 28, 32, and 36-inch widths paired with 36 to 62-inch heights.
What does a window size like '2850' mean?
It's manufacturer shorthand for feet and inches: the first two digits are width, the second two are height. A 2850 window is 2'8" wide by 5'0" tall. A 3040 is 3'0" by 4'0". The actual unit is usually a half inch smaller each way to fit the rough opening.
What size window do I need for bedroom egress in Idaho?
Under the International Residential Code used across Idaho, an egress window needs a clear opening of at least 5.7 square feet, minimum 20 inches wide and 24 inches tall, with the sill no more than 44 inches off the floor. In practice, most casements 2'8"×4'0" and larger and most double-hungs around 3'4"×5'0" qualify — but always check the clear-opening spec for the specific unit, not the frame size.
Are custom window sizes much more expensive?
Less than most people expect. Major manufacturers like Andersen, Marvin, and Milgard build to the eighth-inch as their normal workflow — replacement windows are usually made to your exact opening anyway. Custom sizing typically adds 10–15% versus a stock size, and it beats reframing an opening.
Sources & Testing Data
Last reviewed 2026-07-04 by Wood Windows Inc — (208) 376-2200