You will need a length of 1” (2.5 cm) wide elastic the actual waist measurement plus 1” (2.5 cm) for overlap.

Finished measurements:
Actual Waist circumference: 27( 30.5, 34.5, 38.5, 42.75, 46.25, 50.5, 54.25, 59) cm 68.5( 77.5, 88.5, 97.5, 108.5, 117.5, 128.5, 137.5, 150) cm
Finished length:

Yarn used:
Rowan Alpaca Soft DK
A. 201 Simply White - 5(6, 6, 6, 7, 7, 7, 8, 8) balls
B. 202 Trench Coat - 5(5, 5, 5, 6, 6, 6, 7, 7) balls