How to use this calculator
Start by entering the room name or label for your first window so you can easily identify it later. Then enter the width and height in whole inches plus a fractional component using the dropdown. Select whether you plan to install inside mount or outside mount blinds.
Click the Add Window button to measure additional windows. Each window gets its own card with independent measurements and mount type. You can remove any window entry by clicking the Remove button on its card.
The results section updates automatically as you enter measurements. You will see a summary table with raw measurements, adjusted blind sizes, and square footage. The shopping reference list provides a clean format you can take to the store or use when ordering online.
Inside mount vs outside mount explained
Inside mount blinds fit within the window frame and give a sleek, built in appearance. They work best when your window frame has sufficient depth (at least 2 to 3 inches) and the frame is square and level. The advantage is a clean look that does not cover decorative trim or molding.
Outside mount blinds attach above and beyond the window opening. They are ideal for shallow frames, windows that are not perfectly square, or when you want maximum light blocking. The extra overlap on all sides eliminates light gaps at the edges.
This calculator automatically adds 3 inches to both width and height for outside mount selections. This standard overlap ensures proper coverage while leaving room for mounting hardware above the frame.
Frequently asked questions
What is the difference between inside mount and outside mount blinds?
Inside mount blinds sit within the window frame opening for a flush, built in look. Outside mount blinds are mounted on the wall or trim surrounding the window and overlap the opening by several inches on each side for better light control.
How much extra should I add for outside mount blinds?
The industry standard is 3 inches total (1.5 inches per side) added to both width and height. This provides adequate overlap for light blocking. If you have deep trim or want maximum darkness, consider adding 4 inches instead.
Should I round up or round down my window measurements?
For inside mount, always round down to the nearest 1/8 inch. Blinds that are too wide will not fit into the frame. For outside mount, you can round up slightly since the blinds hang outside the opening and a small extra width is not a problem.
Why do I need to measure at three different points?
Window frames are rarely perfectly square. The width at the top might differ from the width at the bottom by 1/4 inch or more due to house settling or imprecise construction. Measuring at three points and using the smallest ensures your inside mount blinds fit at the tightest spot.
Can I mix inside and outside mount blinds in the same room?
Yes. It is common to use inside mount on standard windows and outside mount on windows with shallow frames or unusual shapes. Matching the blind style and color across both mount types keeps the room looking cohesive even with different mounting methods.