A rule-based, bill-of-materials–driven method for computing the quantities and timing of component purchases and production orders required to meet dependent demand. MRP converts end-item production schedules into net material requirements by using the product structure (BOM), current on‑hand inventory, scheduled receipts, lead times and lot‑sizing rules; it produces planned orders and order release recommendations but does not, by itself, perform finite-capacity scheduling or replace master production scheduling.

Principle

Translate independent end-item demand into time-phased dependent requirements through the bill of materials and schedule order receipts so that materials are available when needed, subject to lead times and lot-sizing rules.

Demonstration

Illustrative scenario → A manufacturer must deliver 100 units of Product A on date D. BOM shows each A needs two Bs and one C. Current inventory: 50 Bs, 10 Cs. Lead times: B = 2 weeks, C = 1 week. Recognition → Planner inputs the master schedule, BOM, inventory and lead times into MRP. Action → MRP explodes demand, nettings inventory, and creates planned orders for Bs and Cs with release dates aligned to lead times. Consequence → Purchase orders and shop orders are timed to produce or procure the shortfall so components arrive before assembly on D.

Misapplication

Treating MRP outputs as a guaranteed, executable shop schedule without checking capacity or ignoring inaccurate BOM/lead-time data. This error treats planned order recommendations as directly actionable work orders, conflating material planning with finite scheduling.

Consequence

Proper use yields time‑phased purchase and production plans that reduce stockouts of dependent parts and clarify procurement timing; misuse (bad data or ignoring capacity) produces excessive work in progress, late orders, or stock imbalances.

Reversal

When production is driven by high variability, very short lead times, or pull‑based methods (e.g., Kanban) and when capacity constraints dominate, MRP’s push, deterministic assumptions fail and a pull or finite‑scheduling approach may be more appropriate.

Boundary

Clearly within → Multi‑level assemblies with dependent demand where BOM, lead times and inventory are defined. Boundary case → Low-volume, engineer‑to‑order products where lot‑sizing and lead‑time variability reduce MRP accuracy. Clearly outside → Independent demand retail items managed by single‑level reorder points without BOM explosion.

Semantic Tension

Push/planned material control (MRP) versus pull/flow control (Just‑in‑Time/Kanban); material timing recommendations versus capacity/finite scheduling constraints.

Synthesis

MRP is a deterministic planning layer that converts product schedules into material actions; its value depends on accurate BOM and lead‑time data and on integration with capacity controls to convert plans into feasible production sequences.