I'm planning to buy a LSD for my 328i, I'm trying to find out what the ratio is currently. Thank You

There are different kinds that you can buy depending on what you want.
I would recommend a 3.73 gear ratio, it has enough torque for low end power and its not to high of a ratio that will limit your top speed.
You can also get 3.62, 4.10.

It is hard to say what axle ratio you now have. There were so many possibilities because of wheel size, automatic (AT) or manual, and customization. Best is to jack the car up and measure it. Many of the BMW rear axles have a small metalic tag on the axle flange that tells you the tooth count of the ring and pinion. I see in a DINAN AD that they were getting the best 328i performance from a 3.15:1 limited slip ratio in 1997.