Window & Door Calculator
Calculate rough opening sizes, total area, estimated cost, and R-value by frame type for window and door replacement projects.
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How to calculate rough opening, area and window replacement cost
For planning, rough opening is usually the unit width plus 1 inch by the unit height plus 1 inch, leaving about 1/2 inch per side for shimming, leveling, insulation and adjustment. A 36 x 48 inch window has 12 sq ft of unit area and a rough opening near 37 x 49 inches. Multiply rough opening area by frame cost per square foot, then add labor per unit for an installed estimate.
Rough openingAdd 1 inch total to width and height for a basic planning allowance.
AreaWindow area = width x height / 144 when dimensions are in inches.
CostFrame material, glazing, trim repair and installation complexity drive the final bid.
Frame R-Value Comparison
| Frame Type | R-Value | Cost/ft² | Notes |
|---|---|---|---|
| Vinyl | R-3 | $25 | Affordable, low maintenance, good insulation |
| Wood | R-3.5 | $40 | Classic look, excellent insulation, needs maintenance |
| Aluminum | R-1.5 | $20 | Durable, slim profile, poor insulation |
| Fiberglass | R-4 | $45 | Premium, strongest R-value, low maintenance |
| Wood-Clad | R-3.7 | $50 | Wood interior, aluminum exterior, premium |
Standard Window Sizes
| Window Type | Width | Height | Rough Opening | Area |
|---|---|---|---|---|
| Single Hung (24x36) | 24" | 36" | 25" x 37" | 6.0 ft² |
| Single Hung (30x48) | 30" | 48" | 31" x 49" | 10.0 ft² |
| Single Hung (36x60) | 36" | 60" | 37" x 61" | 15.0 ft² |
| Double Hung (28x54) | 28" | 54" | 29" x 55" | 10.5 ft² |
| Double Hung (32x60) | 32" | 60" | 33" x 61" | 13.3 ft² |
| Casement (24x48) | 24" | 48" | 25" x 49" | 8.0 ft² |
| Sliding (36x24) | 36" | 24" | 37" x 25" | 6.0 ft² |
| Sliding (48x36) | 48" | 36" | 49" x 37" | 12.0 ft² |
| Picture (48x48) | 48" | 48" | 49" x 49" | 16.0 ft² |
| Picture (60x48) | 60" | 48" | 61" x 49" | 20.0 ft² |
Frequently Asked Questions
What is a rough opening for a window?
A rough opening is the framed opening in the wall where the window sits. It should be 1/2 inch wider and 1/2 inch taller than the window unit on each side (1 inch total wider and taller). This allows room for shimming, insulation, and leveling during installation.
What frame type is best for energy efficiency?
Fiberglass frames offer the best R-value (around R-4.0) and are extremely durable. Wood and wood-clad frames also perform well (R-3.5 to R-3.7). Vinyl is a good budget option at R-3.0. Aluminum has the lowest insulation value (R-1.5) due to thermal conductivity.
How much do replacement windows cost?
Replacement window costs vary widely: vinyl windows average $300-$700 per window, wood $600-$1,200, fiberglass $700-$1,500, and wood-clad $800-$2,000. Labor adds $150-$400 per window. The total cost depends on window size, frame material, glazing options, and installation complexity.