The Ultimate Roman Blind Calculator Guide (2025)
Roman blinds are the epitome of timeless elegance in interior design. They offer the softness of drapery with the functionality of a shade. However, the mathematics behind making them—calculating fabric yardage, pattern matching, and specifically the rod pocket spacing—can be a nightmare for DIY enthusiasts and professional workrooms alike.
Our Roman Blind Calculator eliminates the guesswork. Whether you are working in Imperial (Inches) for a US home or Metric (CM) for a UK project, this tool provides exact cutting dimensions and fold calculations to ensure your blind stacks neatly and hangs perfectly.
How to Measure for Roman Blinds
Before using the calculator, you need accurate measurements.
- Recess Fit (Inside the frame): Measure the width in 3 places (top, middle, bottom) and use the smallest measurement. Deduct 1cm (or 0.5 inch) for clearance. Measure the drop from top to sill.
- Face Fit (Outside the frame): Measure the width of the architrave or window and add 5-10cm (2-4 inches) per side for overlap to minimize light gaps. Measure the drop from where you want the rail to the bottom.
Understanding the Calculations
Our tool performs several complex steps instantly:
- Fabric Cuts: It checks if your window width exceeds the fabric width. If it does, it calculates how many widths are needed (usually 1 central panel and 2 smaller side panels to avoid a center seam).
- Pattern Matching: If you are using patterned fabric, the pattern must match across seams. The calculator adds exactly one vertical pattern repeat per cut to allow for alignment.
- Fold Spacing (The "Cascade"): This is the hardest part. The blind needs to fold up into neat layers. Our calculator determines the "Rod Pocket Spacing" to ensure the bottom section (the "Cascade") matches the other sections or sits correctly based on standard professional practice.
Key Terms Explained
| Term | Definition |
|---|---|
| Headrail Allowance | Fabric added to the top to attach the blind to the batten or rail (usually 5cm / 2"). |
| Hem Allowance | Fabric added to the bottom for the weight bar pocket (usually 5-10cm / 2-4"). |
| Rod Pocket | The horizontal channel sewn into the lining or fabric where the dowel sits. |
| Cascade | The way the folds stack. A "Waterfall" or "Cascade" stack means each fold is slightly longer than the one behind it, preventing bulk. |
Fabric Requirements: Lining and Interlining
Don't forget that for every meter/yard of face fabric, you will usually need the same amount of:
- Lining: Sateen or cotton to protect the fabric from sun.
- Interlining (Optional): A thick, blanket-like fabric added between the face and lining to give the blind volume, insulation, and a luxurious, plush look.
Frequently Asked Questions (FAQ)
How much seam allowance is included? ▼
This calculator provides the Cut Drop (total vertical length). For width, standard join seam allowances (usually 1-2cm) are implied in the "Number of Widths" calculation, but you should verify based on your specific sewing method.
What is the ideal fold depth? ▼
Most professional blinds have a rod spacing between 20cm (8") and 30cm (12"). Smaller windows look better with smaller folds; larger floor-to-ceiling blinds can handle larger folds.
Why do I need a center panel? ▼
If your window is wider than the fabric, avoid a seam right in the middle. It looks unprofessional. Instead, use one full width in the center and split another width into two pieces for the sides.
Start your project
Scroll up and use the #1 Free Roman Blind Calculator now.