There's nothing more frustrating than buying a perfectly-fitting gi, and then finding that it no longer fits right after you wash it for the first time. Arg!
Your first instinct may be to blame the gi company for producing a shotty gi... but before you send off that angry email to customer service (who, by the way, work their tails off and don't deserve your passive aggressive attitude, ya schmuck), you might want to make sure you're washing your gi correctly and the fault isn't your own.
Here are some tips to keep your gi clean, shrink-free and long-lasting:
From the second you pull your brand spanking-new gi out of the bag, you'll need to consider what your first few washes will look like. Does your gi fit loose? Do you like it more fitted? Then wash your gi on hot the first time, try it on again and decide if you need to shrink it a bit more. There's no scientific calculation for the amount shrink you can expect. This is mostly due to the fact that different gi companies use different weaves and fabric weights for their gis. In fact, some companies have numerous gi models that all differ in their construction. The quality of the cotton fibers can also play a role in the amount of shrinkage you can expect, and this is a factor that's controlled at the very beginning of the manufacturing process.
However, as a rule of thumb, you can a lighter weight, looser weave to shrink more than a heavier, tighter weave. Ripstop pants tend to shrink very minimally, if at all.
Again, consider if you need to shrink your gi to make it fit more snug. If you do, then you can pop it into the dryer the first time you wash it. Because almost all gis are made from cotton - at least the jacket, anyway - anytime you dry your gi, it will shrink. The reason for this is that cotton is a natural fiber made of cellulose. When the cellulose fibers are exposed to heat, they constrict, which, compounded over the entire length of the fabric, causes your gi to shrink. It also breaks down the fibers, which weakens the fabric over the long-term and leaves your gi prone to tearing.
Once you've achieved the desirable size for your gi, the best option is to air dry it from then on. If you live in a warm, dry climate, you can dry it outside on a line. However, if the climate is not favorable, or if it happens to be raining on washing day, you can opt to dry it indoors, either on a line or hanging on your bathroom shower rod.
It shouldn't have to be said, but you don't want to just leave your sweaty, un-washed gi in the trunk of your car or in your laundry basket for days on end. While you might think you can just wash that funk out - and gi funk is some serious funk - it's easier said than done. The source of that funk is bacteria - both your body's naturally-occurring ba bcteria as well as the bacteria that may or may not be thriving on the mats - which eat the fatty compounds found in sweat and produce malodorous compounds. These compounds then cling to the natural fibers in your gi, and the longer you leave your gi to "ferment", the harder it is to wash those pesky compounds out, especially if you're washing in cold water to preserve the size and longevity of your gi.
If you can't wash your gi immediately after a training session, there are some ways you can try to "defunk" your gi. These include: adding Borax or color-safe bleach to your laundry, spraying your gi with diluted peroxide (white gis only, as peroxide can bleach certain colors), soaking your gi in a vinegar solution prior to washing, or using a detergent specifically made for gis.
Hopefully these tips will help you keep your gi in tip top shape for your next training session. Just remember the most important tip of all: don't wear a stinky gi to class. You won't make any friends that way.
Train on... fresh. Oss.