Material Requirements Planning (MRP) is a pivotal computer-based system that significantly enhances production planning and inventory control in manufacturing environments. MRP’s primary function is to ensure that materials and components are available for production and customer delivery while maintaining minimal inventory levels.

This system is particularly beneficial in manufacturing scenarios involving multiple items with intricate bills of materials (BOM). However, it is not as effective in job shops or continuous processes that are tightly linked.

What is Material Requirements Planning (MRP)?

Material Requirements Planning (MRP) is a computer-based system used in manufacturing for production planning and inventory control. It ensures that materials and components are available for production, maintains minimal inventory levels, and facilitates the planning of manufacturing activities, delivery schedules, and purchasing.

MRP focuses on managing dependent demand items, derived from the demand for final products, by using inputs such as the Master Production Schedule (MPS), Bill of Materials (BOM), and inventory status records. The system calculates gross and net requirements, time-phases material needs, and schedules planned order releases to optimize the production process.

Objectives of MRP

Objectives of MRP
Objectives of MRP

The primary objectives of an MRP system are:

  1. Availability: Ensure that materials, components, and products are available for planned production and customer delivery.
  2. Inventory Management: Maintain the lowest possible level of inventory to reduce costs and minimize waste.
  3. Planning Activities: Facilitate the planning of manufacturing activities, delivery schedules, and purchasing activities to optimize the production process.

MRP is especially useful for manufacturing environments where the demand for components and subassemblies depends on the demand for final products.

The distinction between independent and dependent demand is crucial here: independent demand pertains to end items, while dependent demand relates to components needed for these end items. MRP systems are designed to handle dependent demand items more effectively.

Inputs of MRP

Inputs of MRP
Inputs of MRP

An MRP system relies on three major inputs to function effectively:

  1. Master Production Schedule (MPS): The MPS details the demand for end items over a set period, including forecasts, customer orders, safety stock requirements, and internal orders. It specifies the quantities of each item needed and their respective due dates. The MPS is derived from demand forecasts and actual customer orders and acts as the starting point for the MRP process.
  2. Bill of Materials (BOM): The BOM is a comprehensive list that outlines all the components, subassemblies, and raw materials required to produce each end item. It includes details such as part numbers, descriptions, quantities per assembly, lead times, and the hierarchical structure of assemblies. The BOM is crucial for expanding the requirements of end items to all lower-level components.
  3. Inventory Status Records: These records provide up-to-date information on all inventory items, including current stock levels, scheduled receipts, and quantities allocated to production. Accurate inventory status records are essential for determining the net requirements of materials by accounting for what is already available versus what needs to be procured or produced.

MRP Computations

The MRP process involves several key computations and steps to ensure materials are available for production:

  1. Gross Requirements: Derived from the MPS and BOM, gross requirements represent the total demand for each component at every level of production.
  2. Net Requirements: Calculated by subtracting available inventory and scheduled receipts from the gross requirements, net requirements determine the actual quantity of materials needed.
  3. Time-Phased Requirements: Aligning net requirements with the production schedule, time-phasing ensures materials are ordered and received just in time for production.
  4. Planned Order Releases: Scheduling the release of orders based on lead times to ensure materials arrive when needed for production.


Consider a scenario where 100 units of Product A are needed in eight weeks. Product A requires one unit of Product B and two units of Product C. Product C, in turn, requires one unit of Product D and two units of Product E.

  • Product A: Requires 100 units of B and 200 units of C.
  • Product C: Requires 200 units of D and 400 units of E.

Given the following lead times:

  • Product A: 4 weeks
  • Product B: 3 weeks
  • Product C: 2 weeks
  • Products D and E: 1 week each

The production release schedule would be:

  • Product B must be available by the end of week four, so its production should start by the end of week one.
  • Product C needs to start production by the end of week two.
  • Products D and E must begin production at the end of week one.

This scheduling ensures that all components are available when needed for the final assembly of Product A.

MRP Process

MRP Process
MRP Process

The MRP process generally follows these steps:

  1. Establish Gross Requirements: Identify the total demand for each component based on the MPS and BOM.
  2. Determine Net Requirements: Subtract available inventory and scheduled receipts from the gross requirements to find the actual quantity needed.
  3. Time-Phase Requirements: Schedule the net requirements to align with the production timeline.
  4. Determine Planned Order Releases: Schedule the release of orders to ensure materials are available when needed, considering lead times.

The planned order releases for all end items aggregate to form the gross requirements for the next level of components, and this process continues until all levels are planned.

Also See: Best Online Six Sigma Certifications

Levels of Items in MRP

In MRP, items are categorized by levels based on the stages of assembly required to produce an end item:

  • Level 0: End items (e.g., Product A).
  • Level 1: Components directly used in end items (e.g., Product B).
  • Level 2: Subcomponents required for Level 1 components (e.g., Product C).
  • Level 3: Further subcomponents (e.g., Products D and E).

Master Scheduling

Master scheduling is a complex process that balances capacity requirements with customer demand and inventory levels. It begins with the Master Production Schedule (MPS), which outlines the anticipated production quantities and timelines for end items. The MPS considers forecasts, customer orders, capacity, and material availability to create a feasible production plan.

The master scheduling process involves:

  • Materials Availability: Ensuring that all required materials are available to meet production needs.
  • Capacity Planning: Confirming that there is enough production capacity to meet demand.
  • Demand Fulfillment: Ensuring that production meets customer demand and forecasted requirements.

MRP Sub-Processes

MRP Sub-Processes
Sub-Processes of MRP

MRP consists of several sub-processes, each critical for effective material planning:

  1. Exploding the BOM: Breaking down the BOM to its lowest level to determine the exact quantities of each component needed.
  2. Netting Out Inventory: Comparing the gross requirements with available inventory to calculate the net requirements.
  3. Lot Sizing: Determining the appropriate order quantities, considering factors like supplier packaging and economic order quantities (EOQ).
  4. Time-Phasing Requirements: Scheduling orders based on lead times to ensure materials arrive just in time for production.

Importance of MRP

Importance of MRP
Importance of MRP

MRP is a vital technique in production and operations management, offering several key benefits:

  1. Cost Minimization: Reduces costs by optimizing inventory levels and minimizing excess stock.
  2. Accurate Material Planning: Ensures precise material requirements to meet production schedules.
  3. Inventory Management: Facilitates better inventory tracking and control.
  4. Delivery Commitment Fulfillment: Helps meet delivery commitments by ensuring materials are available when needed.
  5. Capacity Planning: Provides insights into future capacity requirements.


Challenges of MRP
Challenges of MRP

Despite its advantages, MRP systems face several challenges:

  1. Input Accuracy: The accuracy of MRP outputs heavily depends on the reliability of inputs (e.g., inventory records, BOM accuracy).
  2. Complexity: Operating MRP software requires expertise, and the system can be complex to manage.
  3. Flexibility: MRP systems are often rigid and may not quickly adapt to unexpected changes in demand or capacity.
  4. Lead Time Variability: MRP assumes constant lead times, which may not always be accurate.
  5. Processing Time: Dealing with large volumes of data can lead to high processing times.
  6. Integration with Other Systems: MRP systems must integrate seamlessly with other business processes to be effective.


While MRP focuses on material planning and inventory control, it is often part of a broader Enterprise Resource Planning (ERP) system. ERP extends the principles of MRP to encompass other business functions like finance, human resources, and supply chain management.

Difference Between MRP and ERP

MeaningMRP helps plan material requirements for production.ERP manages day-to-day business activities enterprise-wide.
ObjectiveFocuses on production and assembly planning.Focuses on holistic organizational planning.
ScopeLimited to the production department.Covers multiple departments including marketing and finance.
CostLess costly compared to ERP.More expensive due to broader scope.
ReachLimited customer base.Extensive customer base due to broader application.
Difference Between MRP and ERP

Final Words

Material Requirements Planning is an essential tool for managing production and inventory in manufacturing environments. By ensuring materials are available when needed and maintaining optimal inventory levels, MRP helps organizations meet production schedules and customer demands efficiently.

Despite its challenges, MRP remains a vital component of modern manufacturing and operations management, offering significant benefits in cost reduction, material planning, and inventory management. With advancements in technology, MRP systems continue to evolve, integrating with broader ERP systems to provide comprehensive resource planning and management solutions.

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