How much postage should I apply to this package??

Hi I am a member of swaptree.com and I just completed my first trade. I now have to ship off my item, and I was wondering how much postage it would require? I put the video game in a Scotch Smart Mailer package, it's lined with bubble wrap inside. I'm sure most of you know what the average PS2 game case weighs(with disc inside), so does anyone maybe know how many stamps to apply!! Tyvm!!!