★ CONSTRUCTION · REFERENCE TABLE · WINDOWS
A 36 × 48 inch window needs a 37 × 49 inch rough opening and covers 12 square feet. The planning rule is simple: add 1 inch to each dimension for 1/2 inch of clearance per side. The chart below covers every standard size from 24 × 36 to 72 × 72 inches, and the calculator gives the rough opening and area for any size you enter.
Ordering a window to the wrong opening is an expensive, slow mistake — the unit arrives, the hole is wrong, and the job waits. This chart and calculator remove that mistake for the common sizes: the rough opening is always the window size plus 1 inch each way, and the area is always width times height divided by 144. Measure the unit, read the row, and check the framed hole before you order.
This chart follows a common planning convention, not a building-code requirement: the rough opening — the framed hole the window unit sits in — is the window size plus 1 inch wide and plus 1 inch high, which leaves 1/2 inch of clearance on each side for shimming, squaring, and insulation. So a 36 × 48 inch window needs a 37 × 49 inch rough opening, and its area is 36 × 48 / 144 = 12 square feet. Window sizes are quoted width first, then height, in inches, and areas are quoted in square feet (divide square inches by 144). Always confirm the exact rough opening with the window maker before framing: manufacturers differ, replacement windows are often ordered to the existing opening rather than to a standard size, and local code — not this chart — governs egress, tempered glass, and structural headers.
Setup: window 36 inches wide × 48 inches high.
Line 1 — the rough width. 36 + 1 = 37 inches.
Line 2 — the rough height. 48 + 1 = 49 inches.
Line 3 — the rough opening. 37 × 49 inches.
Line 4 — the area. 36 × 48 = 1,728 square inches; 1,728 / 144 = 12 square feet.
Small bathroom window: 24 × 36 inches. Rough opening 25 × 37 inches, area 6 square feet (864 / 144). Small windows are where the 1-inch rule matters most proportionally — 1/2 inch of clearance is a far larger share of a 24-inch window than of a 72-inch one.
Square picture window: 60 × 60 inches. Rough opening 61 × 61 inches, area 25 square feet (3,600 / 144). A square this size is heavy and usually needs a second pair of hands and a checked header — the chart gives the hole, not the lifting plan.
Wide bedroom window: 72 × 48 inches. Rough opening 73 × 49 inches, area 24 square feet (3,456 / 144). At this width, confirm the header and any egress requirement with the maker before cutting, especially in a bedroom.
| Window size (W × H) | Rough opening (W × H) | Area |
|---|---|---|
| 24 × 36 in | 25 × 37 in | 6 sq ft |
| 24 × 48 in | 25 × 49 in | 8 sq ft |
| 24 × 60 in | 25 × 61 in | 10 sq ft |
| 24 × 72 in | 25 × 73 in | 12 sq ft |
| 36 × 36 in | 37 × 37 in | 9 sq ft |
| 36 × 48 in | 37 × 49 in | 12 sq ft |
| 36 × 60 in | 37 × 61 in | 15 sq ft |
| 36 × 72 in | 37 × 73 in | 18 sq ft |
| 48 × 36 in | 49 × 37 in | 12 sq ft |
| 48 × 48 in | 49 × 49 in | 16 sq ft |
| 48 × 60 in | 49 × 61 in | 20 sq ft |
| 48 × 72 in | 49 × 73 in | 24 sq ft |
| 60 × 36 in | 61 × 37 in | 15 sq ft |
| 60 × 48 in | 61 × 49 in | 20 sq ft |
| 60 × 60 in | 61 × 61 in | 25 sq ft |
| 60 × 72 in | 61 × 73 in | 30 sq ft |
| 72 × 36 in | 73 × 37 in | 18 sq ft |
| 72 × 48 in | 73 × 49 in | 24 sq ft |
| 72 × 60 in | 73 × 61 in | 30 sq ft |
| 72 × 72 in | 73 × 73 in | 36 sq ft |
Every row follows the same rule: rough opening = window size + 1 inch each way, area = width × height / 144 square feet. Sizes are the common planning sizes, not every size any maker sells — if your window is not in the chart, the calculator above gives its rough opening and area directly.
| Output | Formula | What it means |
|---|---|---|
| Rough opening width | Window width + 1 in | 37 in at the defaults — the framed width to cut or check. |
| Rough opening height | Window height + 1 in | 49 in at the defaults — the framed height to cut or check. |
| Unit area | Width × height / 144 | 12 sq ft at the defaults — glass and unit area for ordering and glazing estimates. |
The arithmetic is exact; the convention is approximate. The +1-inch rule is a widely used planning allowance, but manufacturers publish their own rough-opening requirements, and some units — especially replacement, bay, and custom windows — need different clearances, so the maker's sheet overrides this chart whenever they differ. Sizes in the chart are the common planning sizes, not a catalogue: a maker may not sell every combination, and older homes often have non-standard openings that need a custom unit or reframing. Nothing here replaces local building code: egress minimums, tempered-glass locations, fall protection, and header sizing are code and engineering questions, and the rough opening says nothing about any of them. Error policy: empty, zero, or negative dimensions, and dimensions above 240 inches, are reported as errors rather than calculated.
Bright Side Kit. "Standard Window Sizes Chart: Rough Openings & Areas." https://brightoolbox.com/standard-window-sizes-chart/ Accessed October 24, 2026.The framed hole the window unit sits in, before trim. On the planning convention used here it is the window size plus 1 inch wide and 1 inch high — so a 36 × 48 inch window needs a 37 × 49 inch rough opening.
For 1/2 inch of clearance on each side. That gap lets the installer shim the unit plumb, level, and square, and leaves room for insulation around the frame. A hole cut exactly to the window size leaves no room to correct a slightly out-of-square frame.
No — it is a common planning convention, not a code requirement. Code governs egress, tempered glass, headers, and structural matters, but the exact rough opening for a given unit comes from the manufacturer's own specification sheet, which overrides this chart.
37 × 49 inches. Add 1 inch to each dimension: 36 + 1 = 37 wide, 48 + 1 = 49 high. Its area is 36 × 48 / 144 = 12 square feet.
25 × 37 inches, with an area of 6 square feet. For a 60 × 60 window the rough opening is 61 × 61 inches (25 square feet), and for a 72 × 48 window it is 73 × 49 inches (24 square feet).
Multiply width by height in inches, then divide by 144. A 36 × 48 inch window is 1,728 square inches, which is 12 square feet. The calculator above does this for any size you enter.
Yes — width × height is the standard order. A 36 × 48 window is 36 inches wide and 48 inches high; reading the pair backwards would frame the opening the wrong way round.
Use the calculator above. Enter any width and height and it returns the rough opening (each dimension + 1 inch) and the area in square feet — but still confirm the maker's own rough-opening sheet before framing.