When made according to the pattern your mermaid will be approx 6-6.5 tall.
Pattern is detailed with several explanatory pictures.

Materials you will need:
Crochet hook size E/3.50
Worsted weight yarn in the colors you would like your mermaid to be
Tapestry/yarn needle
Polyester stuffing
6 mm safety eyes (alternative- stitch eyes on with black yarn)
Safety eyes can be purchased at craft stores or on Amazon.com

Stitches you’ll need to know:
Chain (ch)
Single crochet (sc)
Half double crochet (hdc)
Double crochet (dc)
Single crochet increase (2sc)
Single crochet decrease (sc2tog)
Slip Stitch (sl st)