Rough-Cut Capacity Planning (RCCP): Units Lie, Hours Tell the Truth

Last month the plant built 2,000 units and the heat-treatment furnace kept up fine. This month the plan is again 2,000 units: 1,000 of family A and 1,000 of family B. Same total, same furnace. By the third week, work is piling up in front of the furnace and orders are slipping. One of those families quietly eats the furnace, and the unit plan could never show it.

Rough-cut capacity planning (RCCP) is a quick check of the production plan against the hours available on a few critical resources, usually per week or per month. It converts units into hours on the machines that decide your delivery dates, before materials are bought and dates promised. Units lie. Hours tell the truth.

How RCCP works: from units to hours

RCCP needs three things:

1. The plan. Usually the master production schedule: quantities by product or family, per week or month.
2. A bill of resources. For each family, how many hours it needs on each critical resource.
3. Available hours. For each critical resource, per period, after shifts, planned maintenance and holidays.

Multiply, add up, compare. You can run it in minutes, while the plan can still change.

Worked example: 1,000 + 1,000 units, 700 furnace hours

The furnace works in loads. A 4-hour cycle holds 20 units of family A, so A needs 4 ÷ 20 = 0.2 furnace hours per unit. Family B parts are bigger: the same 4-hour cycle holds only 8 of them, so B needs 4 ÷ 8 = 0.5 hours per unit.

The furnace has 150 usable hours a week after maintenance, or 600 hours in a four-week month.

Last month: 1,500 A + 500 B. Load: 1,500 × 0.2 + 500 × 0.5 = 300 + 250 = 550 hours. Fits, with 50 hours to spare.

This month: 1,000 A + 1,000 B. Load: 1,000 × 0.2 + 1,000 × 0.5 = 200 + 500 = 700 hours. That is 100 hours over, on the same 2,000 units.

The team moves 250 units of B to next month, where the furnace has room. New load: 1,000 × 0.2 + 750 × 0.5 = 200 + 375 = 575 hours. The month fits.

The monthly total fits. Week 3 does not.

Inside the month, family A runs evenly, 250 units a week, which is 50 furnace hours. Family B follows customer dates: 150, 150, 300 and 150 units in weeks 1 to 4.

• Week 1: 50 + 150 × 0.5 = 125 hours
• Week 2: 50 + 75 = 125 hours
• Week 3: 50 + 300 × 0.5 = 200 hours
• Week 4: 50 + 75 = 125 hours

Total: 575 hours, as before. But week 3 needs 200 against 150, while weeks 1, 2 and 4 each have 25 hours spare.

The fix: build 50 units of B early in week 1 and 50 in week 2. That adds 25 hours to each of those weeks, taking both to 150, and takes 100 × 0.5 = 50 hours out of week 3, which drops to 150. Weeks 1 to 3 are exactly full.

Two checks before approving it. The material for those 100 early units must arrive earlier, so MRP has to confirm it. And three weeks at 100% leave no room for a breakdown, so many planners would still book a Saturday shift in week 3. RCCP makes that call visible early enough to make it calmly.

RCCP is the sketch, the schedule is the blueprint

An architect sketches a house before drawing blueprints. The sketch answers: does it fit on the plot, is the budget sane? Nobody draws the plumbing on it. But if the sketch is wider than the plot, no blueprint will fix it.

RCCP is the sketch: average hours, big buckets, a few resources. The finite schedule is the blueprint: every operation, changeover and hour. A plan that fails RCCP will fail the schedule. A plan that passes can still fail it, because of changeovers or a late component, which is why both exist. See production planning vs scheduling.

Myth: "RCCP has to cover every machine"

Many RCCP projects die trying to model all 80 work centers. RCCP is useful exactly because it is rough. Pick the three to five resources that most often decide delivery dates: the furnace, the coating line, a test bench, a scarce skilled crew. The rest has spare capacity or is left to the detailed schedule.

To find them, look where work waits. The queue in front of a machine says more than its utilization report, as explained in manufacturing optimization starts at the bottleneck.

Where RCCP goes wrong

• Hours per unit are years old. A process changed and nobody updated the bill of resources. Compare it with actuals every quarter.
• Capacity is nominal. Use the hours you can really staff, not 168 a week on paper.
• Setups are ignored. On resources with frequent changeovers, add an allowance per batch.
• Buckets are too big. A monthly check hides week 3. If delivery dates cluster, check weekly.

Who uses the result

RCCP is the operations input to the monthly S&OP meeting. A red week is a question to answer: move volume, add a shift, subcontract, or change a customer date. Someone owns the answer, and the check runs again afterward.

How it looks in factory.online

In factory.online, RCCP shows load against available hours for each critical resource per period, straight from the planned manufacturing orders. The planner sees the furnace at 700 of 600 hours, then week 3 at 200 of 150, and opens a planning scenario to move 100 units of B into weeks 1 and 2. MRP on the same scenario shows whether their material can arrive in time.

If your furnace, press or coating line keeps surprising you in week 3, bring the plan to a demo and we'll run it in hours.