For the afghan I crocheted I used:

I (5.5mm) hook
Black and Vareigated Worsted Weight Yarn
Gauge- 1 ripple = 3 1/2”
example: 11 ripples = 38” wide

Notes: To change the size, add or take away ripples.
For each ripple, chain 14.
Gauge on this is only important in determining how wide your afghan will be.
So if you want to use a different weight of yarn or another hook, just make a swatch to determine your gauge and adjust the width accordingly.