Start with the deadline, not the catalog
A head-count decision only makes sense against a known workload and production window. A shop needing 120 pieces a week has a different requirement from a shop needing 1,200.
Convert the design to real cycle time
Use measured minutes per 1,000 stitches on representative designs, plus handling. Rated SPM is useful for comparing hardware but not enough to promise output.
Apply partial-head utilization
If the average order does not divide cleanly by head count, the final cycle runs with empty heads. Small same-design batches make this penalty more frequent.
Check operator capacity before adding heads
Every extra head adds a garment that needs hooping, loading and unloading. If labor cannot keep up, more heads mostly create idle machine capacity.
Keep a buffer
Do not size a purchase to 100% theoretical utilization. Downtime, rework, proofs, training and unexpected rush work consume real capacity.