Material Requirements Planning (MRP) is a computation-based planning approach that determines what materials are needed, in what quantities, and at what time to fulfill a production plan. The core problem MRP solves is straightforward: manufacturing a finished product requires many components, each of which may have its own sub-components, and each must arrive at the right place at the right time. Without a systematic method, planners rely on intuition or safety stock buffers, both of which create waste or stockouts.
Before MRP existed as a formal discipline, manufacturers used reorder-point systems. A reorder point triggers a purchase when on-hand inventory falls below a predetermined level. This approach works adequately for items with stable, independent demand, but it fails when demand is irregular or derived from a higher-level production plan. A component needed only when a certain product is scheduled should not be replenished on a fixed cycle; it should be ordered precisely when the production schedule demands it.
MRP was formalized in the 1960s and 1970s, largely through the work of production management researchers and early adopters in discrete manufacturing. The fundamental insight was that component demand is dependent on the production plan for finished goods, and that this dependency relationship can be computed mathematically once three inputs are available: the Master Production Schedule, the Bill of Materials, and inventory records. These three inputs remain the pillars of every MRP system today.
The operational goal of MRP is to answer three questions simultaneously: What items are needed? How many are needed? When are they needed? By answering these questions for every component in the product structure, MRP generates planned orders that purchasing and production teams can act on, replacing guesswork with calculated schedules.
MRP also serves a communication function. When a planner releases a planned purchase order generated by MRP, the system has already accounted for lead times, existing inventory, and scheduled receipts. This transparency helps organizations align procurement, production, and finance around a single shared plan rather than independently maintained spreadsheets.
A mid-size manufacturer of industrial ventilation units produces three finished models, each containing a common motor assembly. Using a reorder-point system, the planner would replenish motor assemblies based on average weekly usage, often holding weeks of excess inventory to avoid shortages. After implementing MRP, the system reads the Master Production Schedule, identifies exactly how many units of each model are planned each week, and calculates motor assembly requirements from the Bill of Materials. Purchase orders are generated only when and in the quantity the schedule demands, reducing inventory carrying costs while eliminating production delays caused by unplanned shortages.
- MRP determines what materials are needed, in what quantities, and when, based on the production plan.
- Reorder-point systems fail for dependent demand items because they do not account for production schedule variability.
- The three core MRP inputs are the Master Production Schedule, the Bill of Materials, and inventory records.
- MRP answers three fundamental questions: what is needed, how many, and when.
- MRP provides a shared planning foundation for procurement, production, and finance teams.