MRP (Material Requirements Planning)

Core meaning

Material Requirements Planning (MRP) is a method and supporting system used to calculate which materials, components, and subassemblies are needed, in what quantities, and by which dates to meet a defined production plan or master schedule.

In industrial and manufacturing environments, MRP typically runs inside an ERP or dedicated planning system. It explodes the bill of materials (BOM) for planned finished-goods orders, offsets requirements by lead times, and compares them with current inventory and open supply (purchase orders and production orders) to generate planned orders and rescheduling proposals.

Key elements of MRP

In most manufacturing systems, MRP relies on:

– **Master data**
– Bills of materials (BOMs)
– Item masters and planning parameters (lot size, lead time, safety stock)
– Routings or work centers (sometimes used for lead-time logic)

– **Transactional data**
– Current on-hand inventory
– Open purchase orders and production orders
– Sales orders and forecasts (inputs to the master production schedule)

– **Planning logic**
– *Demand explosion*: converting finished-goods demand into requirements for lower-level components
– *Netting*: subtracting inventory and open supply from gross requirements to get net requirements
– *Time phasing*: offsetting by procurement and production lead times to determine required dates
– *Order proposals*: creating planned purchase and production orders, and reschedule messages

How MRP is used in manufacturing workflows

In regulated and complex industrial operations, MRP is commonly used to:

– Generate planned production orders that feed MES or scheduling systems
– Propose purchase orders for raw materials, packaging, and spare parts
– Identify potential material shortages that could delay production
– Support capacity and finite-scheduling tools (often as an upstream input)

Typically, planners run MRP in the ERP system on a regular cycle (for example, nightly). The resulting planned orders are reviewed, adjusted, and then converted into firm purchase orders or production orders, which may then be dispatched to shop-floor systems.

What MRP is and is not

**MRP includes:**

– Algorithmic calculation of time-phased material requirements
– Logic based on BOM structure, lead times, and inventory positions
– Generation of planned orders and exception messages related to material supply

**MRP does not inherently include:**

– Detailed machine- or line-level scheduling (that is typically finite capacity scheduling or APS)
– Real-time shop-floor control or execution (that is typically MES or SCADA functionality)
– Long-range strategic capacity or financial planning (handled by S&OP/IBP or similar processes)

In many ERP systems, MRP is complemented by **MRP II** (Manufacturing Resource Planning), which adds capacity and resource planning concepts on top of material planning logic.

Common confusion and related terms

– **MRP vs. MRP II**:
MRP focuses on materials. MRP II extends this to include broader manufacturing resources (machines, labor) and often links to financial and capacity planning.

– **MRP vs. ERP**:
MRP is a planning function or module; ERP is the broader enterprise system that may contain MRP along with finance, procurement, sales, and other modules.

– **MRP vs. MES**:
MRP plans *what* and *when* to produce or buy. MES focuses on *how* production is executed on the shop floor, including work-in-progress tracking, quality checks, and compliance records.

– **MRP vs. DRP (Distribution Requirements Planning)**:
MRP plans material supply for production. DRP plans inventory movements and replenishment across distribution networks and warehouses.

Use in regulated and integrated environments

In regulated manufacturing (for example, pharmaceuticals, medical devices, or food and beverage), MRP commonly:

– Drives time-phased procurement of qualified materials from approved suppliers
– Feeds production orders into MES or batch systems that record execution and quality data
– Supports traceability and audit trails by linking demand, orders, and material batches at the planning level

Integration between MRP (in ERP) and shop-floor or quality systems is often important to keep planning data aligned with actual consumption, yield, and nonconformance information.

Relationship to other planning concepts

MRP often operates as one layer within a broader planning hierarchy:

– Sales and operations planning (S&OP) / integrated business planning define aggregate demand and supply strategies.
– The **master production schedule (MPS)** translates these into specific, time-phased production quantities for key items.
– **MRP** then explodes the MPS into detailed component and raw-material requirements.
– Downstream, detailed scheduling tools and MES manage execution against the planned orders generated by MRP.