Bikinis can be quickly and economically made from the fabric of an old T-shirt. Consider using a printed T-shirt for an interesting visual effect on the final product. Cotton swimsuits are best suited for pool side lounging or activities out of the water, though depending on the color and thickness, the fabric can become transparent when wet. Stretchy cotton or jersey fabric can be substituted for the T-shirt, though this can raise the cost of the project.
Lay a T-shirt flat on a work area. Cut off the bottom hem of and discard.
Measure 1 inch from the bottom of the T-shirt and cut around the circumference. Repeat three times, resulting in a total of four 1-inch bands.
Cut one of the bands into two equal sections. Cut the other three bands once to form a strip, resulting in a total of five strips.
Measure nine inches from the bottom of the T-shirt with the tape measure and chalk. Cut off this section. Cut the double fabric in equal halves, resulting in two doubled squares of fabric.
Trace a 10-inch equilateral triangle on each doubled square of fabric. Pin to ensure it will not move during the cutting or sewing process. Cut out to form the beginnings of the bikini top.
Trace a line around two adjacent sides of both the fabric triangles, 1/4 inch from the edge. Fold over at the line and pin securely to form a hem. Sew securely shut with the sewing machine.
Trace a line 1/2 inch from the bottom of the final side of each fabric triangle. Fold over and sew with a 1/-4-inch seam allowance, forming a tube for the bottom strap to be threaded through.
Twist the two shorter fabric strips into a tube-like shape. Sew one strip to the top of a bikini square, at the location where the 1/4-inch seams met. Repeat on the other side.
Twist the long fabric strip into a tube. Thread both of the bikini squares onto the strip, adjusting the location to fit the body-type of the intended wearer.
Lay the second T-shirt flat in the work station. Take a bikini bottom that fits the intended wearer well and lay flat on the T-shirt. Trace around the outline with chalk.
Extend the outline of the bikini bottom 1/2 inch around the sides and 1 inch around the top to allow for a hem. Mark this measurement directly on the T-shirt with the aid of measuring tape and chalk. Cut out around this outline.
Sew the two pieces together at the crotch securely. Mark a line 1/4 inch from the sides of the bathing suit and fold over. Pin securely and sew shut.
Mark 1/2 inch from the top of both the back and front of the bikini bottom in chalk. Fold over and sew with a 1/4-inch seam allowance.
Twist the final two long strips of T-shirt into tubes. Thread through the front and back of the bikini bottom. Center the bottoms on the T-shirt threads to allow sufficient length for tying on each side.