converting down resolution

Hello,
I'm not sure where to post this or how to describe what I want to do but here it goes.

I'm trying to convert the resolution of a video clip from 720x480 to 320x???. Is there a way do the calculation to figure out what that second number should be? Or maybe i'm going about this the wrong way.
I'm creating video clips to be viewed from an iptv server. the quality is great, but I have black bars on the left and right side when viewing which makes me believe that I need to fix the resolution.

Instead of using Compressor I'm using Squeeze.

Thanks.

240. 320x240.


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