Dan,if you are sending a fair amount of chips over time, I recommend either:
(1 ) for about $10 or less, you can buy an electronic postage or food scale. Look for them at either eBay or Google product search:
http://www.google.com/shopping?hl=en&ned=us&q=&tab=if
or (2) make up various samples/combinations in bubble bags and write down weight results at a friendly neighborhood delicacy/grocery store at off hours.

Robt.

don't know anything about these: