To get started, take your measurements: 

Using a tape measure, take your measurements directly on the body; without tightening; take the following dimensions (*If you don't have a tape measure, use regular thread then measure its length with a ruler.) 

For bikini tops, tankini tops and one-piece swimsuits:

Chest circumference is measured horizontally, at the level of the tip of the breasts. You have fallen for a one-piece swimsuit: also measure your waist measurement by placing it at the level of your navel.

For bikini bottoms:

Hip circumference is measured when the legs are close together, surround the hips at the strongest point.

Now that you have all your measurements, you can easily find your swimsuit or bikini size by referring to the chart below: