Calculator Inputs
Example Data Table
| Window width (cm) | Fullness | Panels | Finished width per window (cm) | Fabric widths across (150cm roll) |
|---|---|---|---|---|
| 90 | 1.8x | 2 | ~356 | 3 |
| 120 | 2.0x | 2 | ~520 | 4 |
| 150 | 2.2x | 3 | ~759 | 6 |
Formula Used
Finished Width = (Window Width + 2xSide Returns + Overlap) x Fullness x Ease
Panel Cut Width = (Finished Width / Panels) + 2xSide Hem + Seam Allowance
Length uses window height plus top and bottom allowances. If pattern repeat is set, the length is rounded up to the nearest repeat. Shrinkage and waste are then applied, and the result is multiplied by widths needed across.
How to Use This Calculator
- Measure each garden window’s width and height.
- Pick a fullness factor for your shading style.
- Set returns and overlap for tighter light control.
- Enter roll width to estimate joined fabric widths.
- Add allowances, repeat, shrinkage, and waste margins.
- Press Calculate to show results above.
- Download CSV or PDF for supply planning.
Target width for greenhouse shading
Greenhouse glazing gains heat quickly, so curtain width must cover the opening without leaving bright gaps at the sides or at the meeting point. This calculator starts with window width, then adds side returns and center overlap so the fabric can wrap the frame and meet cleanly. A fullness factor multiplies the base width to create gathers that improve shading and airflow control.
Choosing fullness and panel count
Fullness is the ratio between finished curtain width and the track span. Light filtering shade cloth often works at 1.5 to 1.8, while thicker thermal liners look better at 2.0 to 2.5. Panel count divides the finished width into manageable pieces, helping you match roll widths and reduce bulky seams. More panels can also reduce strain on hooks in humid garden rooms.
Allowances that affect cutting size
Cut width per panel includes two side hems plus optional seam allowance for joining widths. For length, the tool adds top allowance for header tape or pockets and bottom allowance for a weighted hem that keeps fabric from flaring near vents. If the fabric has a vertical pattern repeat, the drop length is rounded up to the next repeat so motifs align across panels.
Shrinkage and waste planning
Outdoor and natural fibers can shrink after washing or steam finishing. Enter shrinkage as a percentage to protect the final fit. The waste margin covers trimming, pattern matching, and edge squaring. Together, these margins produce a purchase length that is realistic for workshop conditions, not just theoretical measurements.
From widths across to total yardage
After calculating total cut width, the calculator estimates how many fabric widths are needed across using your roll width. That count multiplies the adjusted drop length to estimate fabric length per window, then scales by the number of windows. Use the exported CSV for supplier quotes and the PDF for on site cutting lists. For rapid builds, note hardware spacing and recheck measurements carefully before cutting any fabric.
FAQs
How do I measure window width in a greenhouse?
Measure the clear opening between frames, then decide your side returns for wraparound coverage. If using an outside mount, include the trim area you want shaded so the curtain blocks edge glare and drafts.
What fullness factor is best for shade cloth?
For light shade cloth, 1.5–1.8 usually gives enough gather without heavy stacking. If you want stronger light reduction or a softer look, use 2.0. Higher fullness needs more fabric and stronger hardware.
Why does the calculator ask for overlap?
Overlap lets the two center panels cross slightly so sunlight does not leak through the meeting point. It also improves privacy and reduces heat spikes on bright days, especially on south facing glazing.
When should I enter a pattern repeat?
Enter a vertical repeat when the fabric has a repeating motif or stripe you want aligned. The calculator rounds the drop length up to the next repeat so panels match, reducing visible mismatches after hemming.
How do shrinkage and waste affect totals?
Shrinkage increases length to protect the finished drop after washing or steaming. Waste adds a practical margin for trimming, squaring, and pattern matching. Using both helps you buy enough material for clean results.
What do “fabric widths across” mean?
It is the number of roll widths needed to reach your total cut width. If the roll is narrower than required, you join widths with seams. The count multiplies the drop length to estimate yardage or meters.