Calculate capacity for the mix you actually need to make

A line that produced a certain number of units last month does not have a fixed monthly capacity. When the mix changes, the load on each work centre changes with it. A plan based on an average unit can look feasible while the bottleneck is already overbooked.

For a Plant Manager, Operations Director or COO, the useful question is: Can this mix, on these resources and shifts, be delivered reliably? That requires more than dividing available hours by one standard cycle time.

Start with load by product and resource

For each product or variant, multiply the planned quantity by its validated run time at every relevant work centre. Add the setup time for the planned number of batches. Do not spread a long changeover evenly across products if the sequence and batch policy drive the actual loss.

Required load at a work centre = Σ (planned units × validated run time per unit) + Σ (planned batches × setup time per batch).

Then compare that load with practical available time for the same period and resource. This is not a forecast of finished output yet; it is a first test of whether the schedule fits.

Find the constraint for this mix

Calculate the load-to-available-time ratio for each critical work centre. The highest ratio is a candidate constraint, but verify it on the floor: queues, blocked output, material availability and operator coverage can change the conclusion. A different product mix may shift the constraint from assembly to painting, testing or a supplier-fed operation.

In capacity work, I prefer to trace a representative order through the actual route before approving a spreadsheet. This exposes missing operations, shared resources and sequence assumptions that an aggregate hours total conceals. A REFA time study helps establish work content where standards are uncertain, but the planning model must also account for the way products are released and batched.

Use three scenarios, then make a decision

1. Committed mix: load the orders and variants already promised, using validated routings and current shifts.
2. Plausible mix shift: increase the share of the variants that consume the constrained work centre and recalculate the load.
3. Recovery case: test a specific action such as a different sequence, overtime, an alternative resource or supplier support. State the conditions needed for it to work.

Show the gap in hours at the constraint, not just an overall utilisation percentage. A factory can have spare hours in several departments while the one operation needed for the promised mix is saturated.

A capacity review checklist

• Are SAP routings and observed work aligned for the variants driving the load?
• Are setup and changeover hours counted for the actual batch sequence?
• Is staffing available at the constrained operation for the planned shifts?
• Are quality loss, downtime and maintenance assumptions based on a defined period?
• Which customer commitment changes if the mix shifts?
• Who owns the decision to add capacity, resequence or revise the promise?

Capacity is a management decision supported by measured evidence. Keep the assumptions visible so Planning can update the model when demand changes and Operations can explain whether the promise still holds.

EFE Lean combines REFA time studies and capacity validation with Production Consulting to identify the operational constraint and turn the analysis into a usable plan.

Review your capacity assumptions when the planned mix has moved beyond the standards on which your delivery commitments were made.