How window size codes work
Sizes are written width × height. Manufacturer codes often use feet and inches: a 2030 window is 2′0″ wide by 3′0″ high; a 3050 is 3′0″ by 5′0″.
Common size ranges by type
| Type | Common widths | Common heights |
|---|---|---|
| Double-hung / single-hung | 24″-48″ | 36″-72″ |
| Sliding | 36″-84″ | 24″-60″ |
| Casement | 14″-36″ per sash | 24″-72″ |
| Picture | 24″-96″ | 12″-96″ |
| Awning | 24″-48″ | 20″-36″ |
| Basement hopper | 24″-36″ | 12″-24″ |
Ranges are typical; check your manufacturer’s size chart.
How to measure for an insert replacement
- Measure the width inside the existing frame, jamb to jamb, at the top, middle and bottom. Use the smallest.
- Measure the height from the head jamb to the sill at left, center and right. Use the smallest.
- Check the frame is square: measure both diagonals.
Your installer will re-measure before ordering: custom-made windows aren’t returnable.
Bedroom egress sizes
Bedroom windows usually must meet egress rules. See egress windows.
Egress basics
Under the International Residential Code, which most U.S. states and cities adopt in some form, an emergency escape window in a bedroom generally needs:
- A net clear opening of at least 5.7 square feet (5.0 on the ground floor).
- An opening at least 24 inches high and 20 inches wide.
- A sill no more than 44 inches above the floor.
Local codes can differ. Check with your building department before you change a bedroom window's size or style.
Insert or full-frame replacement?
- Insert (pocket) replacement fits a new window inside the old frame. It is quicker and cheaper, but the glass area shrinks a little.
- Full-frame replacement removes the old frame down to the studs. It costs more but lets you fix rot, change the size or improve insulation around the window.
When standard sizes help
New construction and additions can use a manufacturer's standard sizes, which are usually cheaper and quicker to get than custom ones. Plan rough openings to match before framing.