Window coverings: light filtering, room darkening and measured sizes.
How do you compare light control and measured coverage without promising total blackout?
Fabric opacity and edge gaps are different
Hunter Douglas describes how fabric opacity, liners and side features affect room darkening. An opaque fabric does not automatically eliminate light entering around its edges. A sheer, a lined curtain and a cellular shade should be compared by the named product configuration rather than their style name alone.
Record the selected measurement basis
Inside and outside covering measurements describe different extents. Record the supplier’s measurement instructions, actual opening dimensions and the chosen fabric or film product. Do not invent mounting offsets or fixing details from an area estimate.
Calculate the selected fabric or blank
For an illustrative specified fabric span of 3 m and 1.4 m usable stock width, three widths are needed. With a supplied complete 2.6 m drop, stock length is 7.8 m before matching adjustments. That arithmetic does not choose the span, fullness or mounting method.
Keep safety and performance outside a decorative estimate
Child-safe operating systems, egress, heat clearances, film-glass compatibility and mounting must be checked separately with the actual product and appropriate guidance. This article does not claim energy savings, repair tangled cords or certify a covering as safe.
Use the matching calculator
Use this decision sequence
- Record the exact item and the scope described below.
- Check the cited guidance against your product or local growing conditions.
- Measure only the quantities needed for the selected plan.
- Keep the supplied assumptions with the purchase estimate.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Fabric opacity | One product characteristic. |
| Edge coverage | A separate measured configuration. |
| Purchase size | Follow the selected product’s measurement basis. |
Worked comparison
Three full 1.4 m widths at a supplied 2.6 m drop require 7.8 m stock length before any pattern adjustment.
Check before using the estimate
No cord repair, mounting specification or energy-saving estimate is given.
All dimensions, product properties, prices and specifications in this example are illustrative arithmetic inputs. Use the values from your measured plan, selected product data sheet and supplier quote. This guide does not choose construction specifications or certify safety.
Sources and product references
References support the factual distinctions and scope described above. Growing guidance is regional and care instructions are product-specific. Worked numerical examples are independent illustrative arithmetic.
Calculation and scope checked 2026-10-13. Methods and scope.