Capacity Requirements Planning (CRP): How It Works in Manufacturing

Capacity Requirements Planning (CRP) is the bridge between what your MRP system says you need to produce and what your shop floor can actually produce. While MRP calculates material requirements and schedules work orders based on due dates, CRP takes those orders and asks the critical follow-up question: do you have enough capacity at each work center to execute this plan?

Without CRP, you are operating blind — releasing work orders that may overwhelm certain resources while leaving others idle. At User Solutions, we have spent over 35 years helping manufacturers close this gap between material planning and capacity reality.

Where CRP Fits in the Planning Hierarchy

Manufacturing planning operates in a hierarchy, and CRP occupies a specific level:

1. Strategic Business Plan: Sets revenue and growth targets (annual)
2. Sales and Operations Planning (S&OP): Balances demand with aggregate capacity (monthly)
3. Master Production Schedule (MPS): Specifies what to produce and when (weekly/monthly)
4. Rough-Cut Capacity Planning: Validates MPS against aggregate capacity
5. Material Requirements Planning (MRP): Explodes BOM and generates work orders
6. Capacity Requirements Planning (CRP): Validates MRP output against detailed work center capacity
7. Finite Capacity Scheduling: Creates executable, sequenced production schedules

CRP sits between MRP and detailed scheduling. It takes the output of MRP — planned order releases and scheduled receipts — and converts them into capacity demands on each work center. This validation step catches overloads before they become shop floor problems.

How CRP Works: Step by Step

Step 1: Gather MRP Output

CRP starts with two categories of work orders from MRP:

• Released orders: Work orders already on the shop floor, partially complete, with known remaining operations
• Planned orders: Work orders MRP has calculated but not yet released, with all operations ahead of them

Both contribute to capacity demand, but they differ in certainty. Released orders have firm demand at their remaining operations. Planned orders may change as MRP is regenerated.

Step 2: Explode Into Operations

Each work order has a routing — a sequence of operations with defined work centers, setup times, and run times. CRP explodes every order into its individual operations:

Step 3: Time-Phase the Demands

Using the scheduled start dates from MRP (adjusted for lead time offsets between operations), CRP assigns each operation's capacity demand to a specific time period — typically a week, though daily bucketing provides more precision.

The formula for each operation's capacity demand is:

Operation Load (hours) = Setup Time + (Run Time per Piece x Order Quantity)

These loads are accumulated by work center and time period to create a load profile.

Step 4: Compare Load Against Capacity

For each work center, CRP compares the accumulated load against available capacity:

Available Capacity (hours) = Number of Machines x Hours per Shift x Shifts x Efficiency Factor

The comparison produces a load-versus-capacity report, typically displayed as a bar chart or histogram:

Week 20 is critically overloaded — 25% more demand than capacity. This needs resolution before week 20 arrives.

Step 5: Take Corrective Action

CRP identifies problems; planners resolve them. Options include:

• Move work earlier: Pull orders from overloaded periods into underloaded periods (requires material availability)
• Move work later: Push non-critical orders to balance loads (may affect delivery dates)
• Add capacity: Authorize overtime or add shifts at overloaded work centers
• Outsource: Route operations to subcontractors when internal capacity is insufficient
• Adjust the MPS: If capacity gaps are persistent, escalate to the master schedule level

CRP Formulas and Calculations

Required Capacity Per Work Center

Required Capacity = Sum of (Setup Time + Run Time per Piece x Order Quantity) for all orders routed through the work center in the time period

Demonstrated Capacity

Rather than using theoretical capacity, experienced planners use demonstrated capacity — what the work center has actually produced in recent periods:

Demonstrated Capacity = Average Actual Output (hours or units) over the last N periods

This automatically accounts for real-world inefficiencies, breakdowns, and variability without needing to estimate efficiency factors.

Capacity Utilization from CRP

Planned Utilization (%) = (Required Capacity / Available Capacity) x 100

When planned utilization exceeds 100%, the work center is overloaded. When it sits well below target (say, under 60% on a non-constraint), you may have excess capacity that could be redeployed.

Queue Time Estimation

CRP can also estimate queue times based on loading levels. A heavily loaded work center will have longer queues than a lightly loaded one. The approximation:

Estimated Queue Time = Average Processing Time x (Utilization / (1 - Utilization))

At 80% utilization: Queue = Processing Time x (0.80 / 0.20) = 4 x Processing Time At 90% utilization: Queue = Processing Time x (0.90 / 0.10) = 9 x Processing Time

This exponential relationship explains why capacity utilization rates above 90% cause lead times to explode.

CRP vs. Rough-Cut Capacity Planning

Both CRP and RCCP validate capacity, but at different levels of detail:

Think of RCCP as the screening test and CRP as the diagnostic. RCCP quickly identifies major capacity gaps. CRP provides the detailed picture needed for day-to-day planning decisions.

The Limitations of Traditional CRP

Traditional CRP, as implemented in most ERP systems, has important limitations:

Infinite Capacity Assumption

CRP identifies overloads but does not resolve them. It tells you that Work Center 5 is overloaded by 15 hours in week 20, but it does not reschedule jobs or suggest alternatives. The planner must manually figure out what to move and where.

Fixed Lead Time Offsets

CRP uses fixed lead times between operations regardless of current shop conditions. If the standard lead time for an operation is 3 days, CRP schedules it for 3 days — even if the work center is empty and could process it in 4 hours, or so backed up that 5 days is more realistic.

No Sequencing Logic

CRP loads capacity by time period but does not sequence individual jobs within the period. It cannot tell you what order to run jobs on Monday morning — only that Monday's total load is 14 hours against 16 hours available.

No Multi-Resource Awareness

Traditional CRP plans machine capacity and labor capacity separately. It does not check whether a qualified operator is available when the machine is free.

From CRP to Finite Capacity Scheduling

Finite capacity scheduling addresses every limitation of traditional CRP:

• Resolves overloads automatically by sequencing jobs and respecting capacity limits
• Uses dynamic lead times based on actual shop conditions rather than fixed offsets
• Sequences individual jobs within each time period using priority rules
• Schedules multiple resources simultaneously — machines, labor, tooling
• Provides what-if capability to evaluate alternatives before committing

Think of finite capacity scheduling as CRP that does not just identify problems but solves them. RMDB performs this function continuously, maintaining a feasible schedule that respects all capacity constraints across all resources.

Implementing CRP Effectively

Data Requirements

CRP is only as good as its input data. The essentials:

1. Accurate routings: Setup and run times within 10-15% of actual
2. Current work center definitions: Correct shift patterns, machine counts, and efficiency factors
3. Up-to-date MRP: Released and planned orders reflecting current demand
4. Shop floor status: Accurate operation completions so released orders show correct remaining work

Best Practices

• Run CRP at least weekly after MRP regeneration
• Focus on constraint work centers first — overloads at bottlenecks have the biggest impact
• Compare planned vs. demonstrated capacity to validate your efficiency assumptions
• Use CRP to trigger decisions, not just reports — every identified overload should result in an action
• Layer finite capacity scheduling on top of CRP for executable daily schedules

Moving Beyond CRP

CRP is a necessary planning step, but it is not the final answer. The detailed, executable schedule that your shop floor needs requires finite capacity scheduling — a tool that takes CRP's capacity analysis and adds sequencing, constraint resolution, and multi-resource awareness.

Ready to move from capacity identification to capacity optimization? Request a demo of RMDB and see how finite capacity scheduling turns CRP analysis into actionable, executable production schedules.

Frequently Asked Questions

What is Capacity Requirements Planning (CRP)?

How does CRP differ from rough-cut capacity planning?

What inputs does CRP require?

Does CRP use finite or infinite capacity?

How often should CRP be run?