material requirements planning (MRP)

Material requirements planning (MRP) is a systematic method and supporting system logic used to calculate, schedule and manage material supply so that components, subassemblies and finished goods are available when needed to meet a defined production plan. In industrial and regulated manufacturing environments, MRP is typically implemented within an ERP or materials planning system.

Core concept

MRP translates the master production schedule (what needs to be built and when) into time-phased requirements for raw materials, purchased parts and in-house manufactured components. It uses:

• A bill of materials (BOM) to explode parent items into child components
• Inventory balances and reservations to determine what is already available
• Existing purchase orders and work orders to account for open supply
• Lead times and planning rules to offset orders back from required dates

The output is a set of planned supply signals, often in the form of planned purchase orders, planned work orders and rescheduling recommendations, which planners can convert into firm orders and communicate to suppliers and internal production.

Operational meaning in manufacturing

In day-to-day operations, MRP commonly refers to the planning runs and exception messages that drive materials-related decisions, such as:

• When and how much of a part or material to buy from a supplier
• When to release or reschedule work orders for in-house manufactured items
• Identifying potential material shortages, excess stock or obsolete items
• Aligning supplier delivery dates with work-order start dates and ship dates

MRP relies heavily on master data quality (BOMs, routings, lead times), transactional accuracy (receipts, issues, completions) and integration with MES, quality and supplier systems. In regulated environments, it must align with controlled BOMs, approved supplier lists, and traceability requirements without itself serving as the system of record for product definition or quality.

Relationship to suppliers and backlog risk

In the context of supplier management and backlog execution risk, MRP provides the forward-looking demand signal, while suppliers provide confirmation data such as committed dates, capacity constraints and material availability on their side. Planners compare MRP-planned dates to supplier-confirmed dates to assess:

• Whether material will arrive in time to support planned work orders
• Where shortages, slippage or capacity limits could delay execution
• Which parts require expediting, re-planning or alternate sourcing

Effective use of MRP in this context depends on data alignment between purchase orders, part numbers and work orders across buyer and supplier systems.

What MRP includes and excludes

MRP typically includes:

• Time-phased material requirements calculations based on the BOM
• Planned orders and rescheduling recommendations
• Basic planning parameters such as lot sizing, safety stock and lead times

MRP typically does not include:

• Detailed capacity scheduling of machines or labor (handled by capacity planning or advanced planning tools)
• Shop-floor execution control, which is handled by MES or dispatching systems
• Quality management, nonconformance processing or document control

Common confusion

MRP vs. MRP II: MRP focuses on material planning. Manufacturing resource planning (MRP II) extends the concept to include capacity, labor and broader operational planning. Many modern ERP systems mix these concepts, but in strict usage MRP is material-centric.

MRP vs. MES: MRP plans what materials are needed and when. A manufacturing execution system (MES) controls and records how work is actually performed on the shop floor, including routing execution, labor capture, quality checks and traceability.

MRP vs. DRP: Distribution requirements planning (DRP) applies similar logic to replenishing finished goods across warehouses and distribution networks, while MRP concentrates on materials and components feeding production.

Use in regulated and high-mix environments

In aerospace, medical device and other regulated or high-mix, low-volume settings, MRP is used to align material availability with complex, multi-level BOMs, engineering changes and controlled revisions. It often works in conjunction with PLM for product definition and with MES for work-order execution, helping ensure that approved and correct-revision materials are planned to be on hand when specific, traceable work orders are scheduled to run.