I feel a little more information would be helpful.
Are you selling to a wholesaler, grocery store or at the farmers market?
If selling to a wholesaler, what will they accept? By bunches or by ounces? Or does it matter?
What are you growing that you want to bunch?
Abe said, "Traditionally one bunch is however much can be gripped around by your thumb and index finger.
To me this sounds like the simplest way to get workers to bunch what they are picking.