Beginner

How to do capacity planning in manufacturing

A practical method for working out whether you can take on the work in front of you — define your workstations, measure real capacity, lay demand against it, and decide what to do where the two do not fit.

Published

Outcome

You can answer with a number, not a feeling, whether the work you committed to fits the capacity you have. You can also say exactly where it does not fit.

This guide describes a method, not a product. It works with pen and paper, with the free template, or with software. The method is the part that matters. The tool only changes how much of it you do by hand.

Step 1 — Decide what you are counting capacity of

Capacity planning fails at this step more often than at any other, and it fails quietly.

Use the place where work happens as the unit: the mill, the lathe, the deburr bench, the assembly bay, the paint booth.

Do not use the department. It is too coarse to schedule against. Do not use the individual asset separated from its location either. That gives you two lists, and the two lists disagree.

A machine stands at a workstation. Describe the machine by that workstation: what it is, what it can hold, and what tolerances it holds. Do not track it as a separate thing that you must reconcile with a floorplan. One list keeps the plan consistent. Two lists eventually schedule a machine into a bay that is already occupied.

Start with the workstations that constrain you. A shop with thirty workstations usually has four or five that decide its output. Capacity-planning projects die when they plan all thirty in month one.

Step 2 — Establish real capacity, not nameplate capacity

For each workstation, capacity is the work it can absorb in a period. That is usually hours per day.

Take the available hours. Subtract the hours that never go to jobs: setup and changeover, planned maintenance, the first-off inspection, breaks, and the shift that is only half-staffed on Fridays. What remains is the number to plan against.

The theoretical figure looks better, so it is tempting. Resist it. A plan built on nameplate capacity is quietly 20% overbooked from the first day. The overbooking then surfaces as lateness, not as a number that anyone can point at.

If you do not know the real figure, start with an estimate. Correct it after a month of comparison between plan and actual. An honest estimate beats a precise fiction.

Step 3 — Express demand in the same unit

Every committed job must say how much of a workstation it consumes, and when. Hours per day on a named workstation, between a start date and an end date, is enough to be useful.

Two practical notes:

  • Use durations that your shop can estimate. If quoting says “about three days on the mill”, enter three days. If the router says 20 minutes on the saw, enter 20 minutes. Do not invent a precision that nobody believes.
  • Include everything that consumes the workstation, not only the machining. If the job sits in the bay for two days and waits on inspection, the bay is not free.

Step 4 — Lay demand against capacity

This is the whole exercise. For each workstation, and for each day, compare the booked hours against the capacity.

Three results matter.

Under capacity. There is room. This is worth knowing, because it is where the next job goes. Chronic underuse on an expensive workstation is also a real cost.

At capacity. The workstation is full, with no absorption left. Treat this as a warning, not as a success. A shop planned to exactly 100% everywhere has no capacity for the rush job, and rush jobs are not optional.

Over capacity. Two or more jobs want the same place at the same time. This is a decision you did not make yet. It does not become less true while it stays invisible.

Step 5 — Decide, at the overbooked days

There are four ways to resolve an overbooking. Name them, so that the choice is deliberate and not reflexive:

  • Move the job.
  • Extend the capacity, with overtime or a second shift.
  • Move the work elsewhere, to another workstation or another site.
  • Move the commitment. Tell the customer a real date.

Shops avoid the last option. It costs least when you take it early. A date renegotiated three weeks out is a conversation. The same date missed on the day is a relationship.

Step 6 — Choose a horizon and a cadence

Plan far enough ahead to act. For most shops that is four to twelve weeks. Beyond that, demand is too speculative to schedule, and the effort is wasted.

Review on a fixed rhythm. Weekly is typical. Review again after any event that invalidates the plan: a rush order, a breakdown, or a late delivery.

A capacity plan updated only when somebody remembers is worse than no plan at all. People trust it while it is wrong.

The failure mode to watch for

Capacity planning collapses when the plan costs more to maintain than it saves. That is usually not a problem with the method. It is a problem with the mechanics.

If every change means that you rebuild a grid by hand, the plan falls behind reality. Once it is behind, the shop stops trusting it and asks the shop floor again.

So keep the plan as coarse as you can. Automate the comparison in Step 4 if you can. Be honest when the manual version stops keeping up. That moment has a recognizable set of symptoms.