You can find a detailed guide here.
Here’s a short version of it:
Take a cloth or plastic soft tape measure that you can find at craft and sewing stores. If you don't have any, you can get a piece of string and a ruler.
You need to strip down to your underwear or wear tight clothing like leggings to get accurate measurements.
Bust – wrap a centimeter around the most volume and the protruding part of the chest, exhale halfway and fix the volume.
Waist – wrap a centimeter around the thinnest part of the waist, measure at half a breath. Do not retract or inflate the belly during the measurement.
Hips – it is measured on the most volume part of hips, approximately at the level of the hip joints.
Then compare your notes with our size table.
Depending on the item you want to buy, you may need to measure other indexes as well. If that is so, please, proceed to our full guide by the following link.
Feel free to contact us to get assistance with your measurements and picking a proper size.