Although martial arts GI/Do-Bok are labeled in sizes like 1 to 7, the sizes from brand to brand can be very different. If you can't try on the uniform, then select it by the size chart that particular brand uses. Some uniform brands also come in half sizes. To show you how different the different brands and sizes are, I wear a #4 in one brand, a #4-1/2 in another and a #3 in one. Yet all of them fit well. Either try one on, or use their size chart. If ordering you might even call the seller and ask them.
Best of Luck!