There are two methods for finding your salwar kameez size—calculating your size from your actual bust measurement (described in a previous post), or measuring your size from a kameez that fits (described below).
Method 2. Measure your favorite kameez
You'll need a soft tape measure and a kameez that fits well, preferably one that doesn't have much stretch to the fabric. Lay it flat, right side out, and smooth out any wrinkles. Measure from side to side (in inches) across the widest part of the bust area (this is usually immediately below the sleeves). Now that you've measured across the front, add the same amount again to account for the fabric across the back. The total is your kameez size.
In other words, the kameez size is actually the measurement around the kameez bust, in inches. This system might seem odd if you're used to US sizes, but it's quite practical. You can find the size of any salwar kameez suit quickly if you have a measuring tape, and that's a good thing since size labels in salwar shops in the US are notoriously inaccurate.
The downside is that kameez size doesn't take body proportions or height into account, unlike US sizing. Even with US sizing, though, few brands are so consistent that most women can pick just one size before heading into the dressing room to check fit.
As with US clothing, just because a kameez is the right size doesn't mean it will fit well. Alterations are a fact of life for women who are tall, petite, busty, hourglass-shaped, long-waisted, or broad-shouldered. Many salwar stores in the US have a tailor onsite or can recommend an Indian tailor locally. In the long run, it's often simpler and less expensive to learn to order salwar kameez tailored to your measurements. That, however, is a subject for another day!
Note: if you send measurements to a tailor, specify whether you are sending body measurements (your actual measurements) or garment measurements (taken from a kameez that fits you.) The tailor will sew clothing to the exact garment measurements, but will add 2-3 inches (US "ease"; India "loosing") to body measurements so you'll be able to move and breathe freely when you're wearing your new salwar suit.