Formula and example
How it is calculated
waist radius = (waist + ease) / (2π × circle fraction)
Worked example
72 cm waist and 2 cm ease for a half circle gives a waist radius of 23.5549 cm.
Things to check
- The bounding rectangle and area are not a purchasing cutting plan. Allowances for side seams, zip, waistband, grain direction, pattern matching, and fabric faults are not included.
- The finished waist opening may not necessarily pull over the hips: closure and wearability must be planned separately. Check for stretching due to bias grain with a test piece.
Frequently asked questions
Why is the inner cutting radius smaller than the waist radius?
The seam allowance left at the waist edge moves towards the centre of the cut. Thus, the waist circumference measured on the seam line remains the desired size.
Does it specify the total fabric to buy?
It shows the geometric bounding size. Due to grain direction, side seams, pattern matching, zip, and waistband, the actual cutting plan is a separate task.