Multiple-window comparison
Compare several window units using one clearance value.
| Window | Unit size | Quantity | Rough opening | Total area |
|---|
Saved calculation history
Formula used
Use manufacturer dimensions before ordering materials. Check framing plans before cutting lumber. Final measurements must match approved project requirements exactly.
How to use this calculator
- Enter the actual window unit width and height.
- Select one measurement unit for all dimension fields.
- Choose equal or separate installation clearances.
- Add shim, header, or sill-pan allowances when required.
- Adjust framing quantities for a planning estimate.
- Enable the editable egress check when needed.
- Review results before ordering or cutting materials.
Example calculations
| Window size | Side clearance | Top clearance | Bottom clearance | Rough opening |
|---|---|---|---|---|
| 36 × 48 in | 1/2 in | 1/2 in | 1/2 in | 37 × 49 in |
| 48 × 60 in | 3/8 in | 1/2 in | 1/2 in | 48 3/4 × 61 in |
| 1200 × 1500 mm | 10 mm | 10 mm | 10 mm | 1220 × 1520 mm |
Measurement and framing guidance
Measure the window unit at several points. Use the largest verified unit dimension. Keep every measurement in one unit system.
Clearances support shimming, leveling, and insulation. Excessive gaps can weaken installation support. Manufacturer instructions should control final opening dimensions.
Headers and studs carry structural loads. Their sizing needs approved engineering guidance. Never rely only on material estimates here.
Frequently asked questions
What is a window rough opening?
It is the framed opening receiving the window. It exceeds the window unit dimensions slightly. This space permits alignment, shimming, insulation, and sealing.
How much larger should the opening be?
The required difference varies by window system. Manufacturer instructions provide the controlling dimensions. Always verify them before framing the opening.
Can I enter fractional inches?
Yes, mixed fractions are accepted in text fields. Enter values like 36 1/2. Decimal values also work correctly.
Does the calculator support metric measurements?
Yes, select millimeters or centimeters. All related fields use that selection. Results also show converted metric dimensions.
What does shim space add?
Shim space adds extra width on both sides. It remains separate from basic clearances. Use it only when your installation requires it.
Is the framing estimate structural design?
No, it provides planning quantities only. It cannot size load-bearing headers safely. Use approved plans and qualified guidance.
How does the egress check work?
Enter actual clear opening dimensions and sill height. Then enter your applicable limits. The calculator compares each value separately.
Can replacement windows use this calculator?
Yes, choose the replacement installation option. Measure the existing opening very carefully. Follow the replacement window manufacturer instructions.
Why is the rough opening area useful?
It supports planning for wall openings and materials. It also helps compare multiple windows. Structural calculations still require separate analysis.
Can I save previous calculations?
Yes, use the save button after calculating. Data remains in your browser storage. Clearing browser data removes saved entries.
How do I create a PDF?
Select the Print or PDF button. Choose PDF in your print dialog. Review the preview before saving.