Make a your own pattern for a mermaid tail that fits like a glove. Sew this tail from a shimmery stretch knit fabric and wear it with a strapless top or a bikini top adorned with cut outs of seashells. Add ropes of pearls and a hair ornament in the shape of a starfish to complete the costume. This version is for a situation where the wearer can be seated the entire time they have it on. It is good for a play or photographs.
Have the wearer put on yoga trousers some or other garment that fits close around her hips and thighs. Have her stand with her legs together.
Measure around the wearer's body at the hips. Move up 3 inches and measure around her body at this point. Call this the waist measurement even though it will be below her natural waist. Move down 3 inches from the point where you took the hip measurement and measure around her thighs at this point. Keep measuring every three inches down her thighs until you are below her knees. Call the last measurement the knee measurement. Keep the tape measure parallel to the floor for all the hip and thigh measurements.
Measure the distance from the knee measurement to the widest part of her calves then measure around her calves. Measure the distance from the knee measurement to her ankles and then measure around her ankles.
Divide all the measurements that were made around the hips and legs by four and add 1/2 inch for seam allowances.
Lay a 3-foot-by-4-foot sheet of paper on a large surface with a 3-foot edge at the top. Draw a line down the middle of the paper, parallel to the 4-foot sides. Starting with the hip measurement draw a line on the right side of this centre line equal to the distance you calculated using the hip measurement. This line should start at a point 4 inches below the top of the paper. The line should be perpendicular to the centre line.
Measure 3 inches down from the hip line and mark the distance you calculated from the next measurement on the right side of the centre line. Draw the rest of the distances you calculated moving 3 inches down the centre line for each line until you reach the knee measurement. Draw the line for the knee measurement. Draw the lines for the calf and the ankle measurements the distances you measured below the knee measurement.
Draw the line for the top measurement along the top edge of the paper, 4 inches above the hip line. The extra inch allows you to fold down an inch of fabric at the waist of the tail.
Draw a 1 foot line on the right side of the centre line 12 inches below the last line you drew and parallel to it. This will be the bottom of the fin at the end of the tail. It should be parallel to the other lines. Draw an arch that connects the right end of this line to the right end of the ankle line.
Draw a smooth curve that connects the ends of all the lines on each side from the waist to the ankle.
Fold the paper in half along the centre line and cut both layers of paper along the outside lines you drew. This your pattern. Use it to cut two pieces of fabric, one for each side of the tail.
You may shape the bottom of the tail fin into two large scallops or a row of zigzags or scallops. You may want to stiffen the fin with cardboard when you make up the tail.