Do yourself a favour & buy a cheap scale.

You can get a simple hanging postal scale for aout $5 if you order it - you just clip the baggy on and it measures the weight while it dangles. (just checked Amazon has it for $5 exactly)

They also have them in auto parts stores - they use them to weigh bearings or something to rebuild cards - can't quite remember which. I think they're about $10 there, but it's been years since I've bought one.

Safer than carrying a digital scale - some cops use having pot with a scale as grounds to charge you with intent to distribute. We always kept the scale at home, then complained later if it was light. Never had anyone who didn't take care of the problem. And, some people will weigh right in front of you if you ask - just kind of depends on where you are.