The engineering question
Define the good-part demand, allocated part and runner mass, expected unrecovered loss, allowable regrind, and package basis. Keep runner recovery and startup purge separate from routine scrap.
What to document
A purchase estimate is only as defensible as the mass source and material-accounting policy behind it.
Practical workflow
Start with Resin Weight, then use Resin Purchase Quantity and Regrind Blend.
Validation boundary
Use manufacturer documentation, grade-specific supplier data, controlled process records, and trials for any equipment, quality, material, or commercial commitment. A static calculator is a transparent starting point, not a simulation or approval.