how do u know if fits good
 

im talking about length. if the bottom of the jacket meets the body's waist? or a little under it?
its cuz my jacket is nice snug fit, but the length is little short (i think) when in riding position air gets in the back of my waist. should i get one size up or..thanks.

What kind of jacket is it? Is there a way to perhaps strap it to your belt?

That's probably about right but it's hard to say without pictures. My leather jacket does that too when I'm riding and the guys at the shop said it was the perfect fit for me. Most people on the street wear jackets that are too big for them.

Mines short too, always kinda bugged me but it seems everyone elses jackets fit the same unless they went a size too big.

it is literally right at the waist and the sleeves go right at the wrist. But when in riding position, everything changes. so im thinking of going bigger one size and everything should be fine. what u guys think?

same as mine, but as I was told when I bought it you want the jacket to fit snug because if it doesn't it will slide and wont protect you. I wear a large shirt, and went with a medium jacket. Id rather be safe.

Different brands and styles have different lengths. I have a Joe Rocket jacket that is a little longer and fits lower on my waist when I ride, and a Speed and Strength jacket that doesn't even reach my waist when on the bike. You want the overall fit to be right most of all. If the padding is not in the right places, you will not be protected in case of a crash. On the other hand, if the jacket is too short, you may get cuts/injuries around your waist as well. Its mostly personal preference, but I wouldn't recommend going with a bigger size for a longer length. try a different brand or style first.