Ebay sellers, help with how figure out N64 game shipping costs

Hello, I've recently been ramping up my N64 collection to another level; and I have four loose games that don't meet my collection expectations lol.

How do you figure out shipping and packaging costs ahead of time without going to post office (Weight + box dimensions)? I will buy the box/envelop from UPS. Is there a quick and easy online utility that will figure this out for me?

Thank-you!