You now have the finished blind width and length. Next you need to calculate the number of folds in the roman blind as it is pulled up. The blind will have standard folds where the folds lie on top of each other when the blind is pulled up.
STANDARD FOLDS CALCULATION
First we need to establish the Headrail Allowance
The headrail allowance must be sufficient to cover the batten face and allow enough room for the blind to pull up underneath the batten without it hitting the batten/eyelets before it is fully up (with all the folds hanging inline with each other).
As a general rule use an absolute minimum headrail allowance of:
Traditional batten: Batten face + 3.5cm Headrail mechanisim: Headrail depth + 2.5cm
Please see our BLOG entry HEADRAIL ALLOWANCE EXPLAINED for more detail*Note the depth of the blind when pulled up will be equal to the headrail allowance plus the depth of the fold (one pleat section).
Alternatively try our online calculator.
I think you are saying you are making 11 roman blinds not curtains and the width of the blinds varies from 80cm to 85cm?
We always make blinds by sewing the rod pockets on/into the lining before attaching the lining to the fabric (STEP 5). this avoids stitching lines through to the face fabric. The lining and is later stab stitched to the fabric in STEP 8 to give the blind the stability you are talking about.
With blackout lining you will see pinpricks of light on the rod pocket stitch lines regardless of which way you do it if you sew the rod pockets on/into the blackout lining. We make blackout lined blinds by sandwiching blackout lining in-between the fabric and lining that way the rod pocket stitch lines are on the lining not the blackout. Even with this technique you still get some small pinpricks of light where the stab stitches are. (we plan to make that tutorial)
We do not use wooden dowels (rods) but use fibreglass rods which are also light. The purpose of the rods is not for weight but to form a rigid line at the fold when the blind is pulled up. The bottom bar needs some weight an for this we use an white coated aluminium flat bar.