Window Area Calculator
Free Window area Calculator for architectural & design projects. Enter dimensions to get material lists and cost estimates.
Formula
Area = Width x Height (rectangular) | Area = W x (H - W/2) + pi(W/2)^2 / 2 (arched)
Rectangular windows use simple width times height. Arched windows combine a rectangular section with a semicircular top. Circular windows use pi times radius squared. All areas convert between square inches, square feet, and square meters.
Worked Examples
Example 1: Standard Double-Hung Windows
Problem: Calculate total glass area and material costs for 8 rectangular windows, each 36 inches wide by 60 inches tall.
Solution: Single window area = 36 x 60 = 2,160 sq in = 15.00 sq ft\nPerimeter = 2 x (36 + 60) = 192 inches = 16.00 ft\nTotal area = 15.00 x 8 = 120.00 sq ft\nGlass cost per window = 15.00 x $12 = $180\nTrim per window = 16.00 x 1.1 x $3 = $52.80\nTotal cost = ($180 + $52.80) x 8 = $1,862
Result: Total Area: 120.00 sq ft | Total Trim: 140.80 ft | Est. Cost: $1,862
Example 2: Arched Entryway Window
Problem: Calculate the area of 2 arched windows, each 48 inches wide by 84 inches tall.
Solution: Radius of arch = 48/2 = 24 inches\nRectangular portion = 48 x (84 - 24) = 48 x 60 = 2,880 sq in\nSemicircle portion = pi x 24^2 / 2 = 904.78 sq in\nSingle area = 3,784.78 sq in = 26.28 sq ft\nTotal area = 26.28 x 2 = 52.56 sq ft\nPerimeter = 48 + 2(60) + pi(24) = 243.40 in = 20.28 ft\nTotal trim = 20.28 x 1.1 x 2 = 44.62 ft
Result: Single: 26.28 sq ft | Total: 52.56 sq ft | Total Trim: 44.62 ft
Frequently Asked Questions
How do you calculate the area of a rectangular window?
To calculate the area of a rectangular window, multiply the width by the height using matching units. For example, a window that is 36 inches wide and 60 inches tall has an area of 36 x 60 = 2,160 square inches, which equals 15 square feet when divided by 144. Most residential windows are measured in inches but building codes and material orders typically use square feet. When measuring, take the width at three points and use the smallest measurement to ensure proper fit. For rough opening calculations, add 1/2 inch to each side for shimming space. Remember that the actual glass area is smaller than the frame opening due to the frame, sash, and muntins.
How do you calculate the area of an arched or half-round window?
An arched window combines a rectangular bottom section with a semicircular top. Calculate the rectangular portion by multiplying the width by the straight-wall height (total height minus the radius of the arch, which equals half the width). Then calculate the semicircular arch area using the formula pi times radius squared divided by 2, where the radius is half the window width. Add both areas together for the total. For example, an arched window 36 inches wide and 72 inches tall has a rectangular section of 36 x 54 = 1,944 square inches plus a semicircular section of 3.14159 x 18 squared divided by 2 = 508.9 square inches, totaling approximately 2,453 square inches or 17.0 square feet.
What is the standard window-to-floor area ratio for residential buildings?
Most building codes require a minimum window area equal to 8 percent of the floor area in habitable rooms, though this varies by jurisdiction and climate zone. The International Residential Code specifies a minimum of 8 percent glazing area to floor area for natural light. For ventilation, at least half of the required window area must be operable. Energy-efficient design guidelines recommend 15 to 20 percent window-to-floor ratio for optimal balance between natural daylight and thermal performance. South-facing windows in the Northern Hemisphere can be larger at 20 to 25 percent because they gain beneficial solar heat in winter. North-facing windows should be minimized to 10 to 15 percent to reduce heat loss during cold months.
What formula does Window Area Calculator use?
The formula used is described in the Formula section on this page. It is based on widely accepted standards in the relevant field. If you need a specific reference or citation, the References section provides links to authoritative sources.
Can I use Window Area Calculator on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.