Window Rough Opening Size Calculator
Find the rough opening size to frame for a window or door from its unit size and clearances.
Compare Your Options And Get Clear Answers
Find the rough opening size to frame for a window or door from its unit size and clearances.
Window Rough Opening Size Estimator
Enter your numbers below for an instant estimate.
How It Works
Key concepts behind this calculator
Enter Values
Fill in each field with your own numbers.
Calculate
Results update as you change the inputs.
Review
Read the breakdown and the explanation.
Adjust
Change values to compare scenarios.
Window Quick Guide
Typical values for reference.
| Unit W mm | Unit H mm | Gap mm | Rough opening |
|---|---|---|---|
| 600 | 900 | 20 | 620 x 920 mm |
| 1200 | 1400 | 20 | 1220 x 1420 mm |
| 1800 | 1500 | 20 | 1820 x 1520 mm |
| 2400 | 2100 | 20 | 2420 x 2120 mm |
| Rule of Thumb | Check inputs | Use as a guide | Round sensibly |
Window Rough Opening Calculator FAQ
Answers to common questions about this calculator.
The framed hole in a wall that the window sits in.
Usually 10 to 25 mm per direction, per the maker.
Rough opening = unit size + clearance each way.
It is an estimate based on the inputs you enter. Check real quotes, labels or official guidance for important decisions.