You need a soft measuring tape and a fitted top. Stand relaxed — do not hold your breath or pull the tape tight.
Bust: around the fullest part of the chest, tape level under the arms and parallel to the floor. This is the number our size chart is built on.
Waist: around the narrowest part, usually an inch above the navel. For a kurti this decides comfort; for a churidar or palazzo it decides everything.
Hip: around the fullest part, roughly eight inches below the waist. If your hip measurement puts you in a bigger size than your bust does, order the bigger one for A-line and straight cuts.
Shoulder: from the bone at one shoulder tip across to the other. Useful for fitted kurtis.
Length: from the shoulder seam straight down to where you want the hem.
Two things to remember. Indian labels add ease, so a size M kurti is stitched a couple of inches larger than a 36 inch bust — you do not need to size up “for comfort”. And if you fall between two sizes, size up for cotton, which shrinks a little, and stay true to size for rayon, which does not.
Every product page carries the exact garment measurements. Compare them with your own numbers rather than trusting the letter on the label.