How to Calculate Window Rough Opening
What is Window Rough Opening?
Window Rough Opening Calculator helps contractors and tradespeople accurately size, spec, and estimate materials and systems.
Formula
RO Width = Window Width + 0.5 inch; RO Height = Window Height + 0.5 inch
Step-by-Step Guide
- 1Add 1/2 inch to each dimension for shim space
- 2Apply the formula using your project measurements
- 3Add required safety factors or waste allowances per code
Worked Examples
Input
36 × 48 inch window unit
Result
RO = 36.5 inches wide × 48.5 inches tall
Common Mistakes to Avoid
- ✕Not applying code-required safety factors or derating
- ✕Forgetting to account for waste and cut losses in material estimates
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