Manufacturing operations involve a level of complexity that goes well beyond what accounting or inventory modules can handle alone. You need to plan what to produce, when to produce it, and what materials are required. You need to track production in progress, manage the shop floor, and measure actual performance against planned costs. And you need to do all of this while staying connected to your inventory, purchasing, and financial modules so that every production activity flows through to the right places in the business.

This is what the ERP manufacturing module addresses. Understanding it starts with understanding the evolution from MRP to MRP II to ERP — and what each step added to the picture.

MRP, MRP II, and ERP Manufacturing: What Changed

Material Requirements Planning (MRP)

Material requirements planning was developed as a systematic approach to answering a specific question: given what we need to produce and when, what materials do we need, and when do we need them? MRP calculates material requirements by exploding bills of materials against planned production quantities and netting against existing inventory and open purchase orders.

MRP is fundamentally a planning calculation. It tells you what to order and when to order it to meet your production schedule. What it doesn’t handle is the operational reality of the factory floor — capacity constraints, machine schedules, actual labor hours, or the feedback loop from production back to planning.

Manufacturing Resource Planning (MRP II)

MRP II extended the original concept to include capacity planning and shop floor control alongside material planning. It added the ability to plan against machine and labor capacity, track actual production results, and measure performance against the plan. MRP II also connected the manufacturing plan to financial planning — so production costs could be tracked and variance analysis could be performed.

ERP Manufacturing

ERP manufacturing integrates the MRP II capabilities with the rest of the business: procurement, inventory, quality management, customer orders, and financial accounting. When a production order consumes materials, inventory is updated and cost is recorded. When a finished good is produced, it enters inventory and drives the accounting for work-in-progress and finished goods. The manufacturing module is no longer a standalone planning system; it’s connected to every other operational and financial process.

Bill of Materials

What a Bill of Materials Is

The bill of materials (BOM) is the foundational data structure in any manufacturing ERP. It defines what a product is made of — every component, sub-assembly, and raw material required to produce one unit of the finished good, along with the quantity of each item needed.

BOMs can be single-level (the parent item and its immediate components) or multi-level (the parent, its components, and the sub-assemblies that make up those components, all the way down to raw materials). Most manufactured products have multi-level BOMs.

Types of BOMs

• Engineering BOM (EBOM): The product structure as defined by engineering, showing what the product is designed to contain
• Manufacturing BOM (MBOM): The product structure as used in production, which may differ from the EBOM if certain components are grouped or sequenced differently for manufacturing purposes
• Sales BOM: A configuration-oriented BOM used when products are sold in kits or bundles that need to be picked and shipped from components

BOM Management

The ERP BOM module needs to handle version control (products change; you need to track which version of the BOM was used for any given production run), effectivity dates (a component change takes effect on a certain date; the system needs to apply the right version at the right time), and BOM comparison tools that help engineers understand what changed between versions.

Routings

What Routings Define

A routing is the sequence of operations required to manufacture a product. Where the BOM defines what materials are needed, the routing defines how the product is made — which work centers are involved, what sequence operations follow, and how long each operation takes.

Routing Element	What It Describes
Operation	A defined manufacturing step (e.g., cutting, welding, painting)
Work center	The machine, cell, or labor group that performs the operation
Setup time	Time required to prepare the work center before the operation begins
Run time	Time per unit to perform the operation
Queue time	Expected wait time before the operation starts
Move time	Time to move the work-in-progress from one work center to the next

Routings feed into capacity planning (knowing how much machine and labor time each production order requires) and shop floor control (guiding workers through the production process step by step).

MRP Planning

How MRP Calculates Requirements

MRP works through three inputs:

1. Master production schedule (MPS): What you plan to produce, in what quantities, and when
2. Bill of materials: What each product is made of
3. Inventory data: What you already have on hand or on order

From these, MRP calculates what materials you need to have on hand at each point in time to meet your production schedule. It accounts for lead times to back-schedule when each material needs to be ordered or produced. The output is a set of planned purchase orders and planned production orders (for sub-assemblies made in-house).

Netting Logic

MRP nets demand against supply at each level of the BOM:

• Gross requirement: How much of an item do you need?
• Scheduled receipts: How much is already on order and due to arrive?
• On-hand inventory: How much do you already have?
• Net requirement: The difference, if positive, drives a new planned order

Planning Parameters

MRP behavior is controlled by item-level planning parameters that your team configures: lot sizing rules (order in exact quantities, in fixed multiples, or to cover a certain number of weeks of demand), safety stock, lead times, and planning horizons. Getting these parameters right is one of the most important and most overlooked aspects of an ERP manufacturing implementation.

Production Orders

Creating and Managing Production Orders

A production order (sometimes called a work order or manufacturing order) is the authorization to produce a specific quantity of a product by a specific date. Production orders can be created manually or generated automatically from MRP. Each production order references the BOM (which materials to consume) and the routing (which operations to perform).

The production order lifecycle typically flows:

Created → Released → In Progress → Completed → Closed

At each stage, the system tracks what has happened against the order: materials issued, operations performed, labor hours recorded, output quantities received into inventory.

Work-in-Progress Tracking

As a production order progresses through operations, the ERP tracks the status of work-in-progress. Materials are issued from inventory to the production order when they’re consumed in production. Output quantities are recorded as operations are completed. This tracking feeds the costing system — accumulated material costs, labor costs, and overhead determine the cost of the finished goods produced.

Shop Floor Control

What Shop Floor Control Adds

Shop floor control (also called production execution or manufacturing execution) extends production order management to the real-time tracking of what’s happening on the production floor. It answers questions like: which production orders are running right now, which work centers are busy, what is the queue at each work center, and what have workers actually produced in the past hour?

ERP shop floor control typically supports:

• Work center scheduling: Assigning production orders to specific work centers and time slots
• Labor tracking: Recording labor hours against specific operations and production orders
• Operation reporting: Workers reporting completion of operations (via a terminal, tablet, or barcode scanner on the shop floor)
• Scrap and rework reporting: Recording units scrapped or sent for rework, and attributing the cost appropriately

Backflushing

Some manufacturers don’t report labor and material consumption at each operation — instead, they report only when the finished good is produced, and the system “backflushes” the material consumption and labor hours based on the BOM and routing. Backflushing reduces data entry burden but sacrifices real-time visibility into work-in-progress.

Capacity Planning

Rough-Cut Capacity Planning

Rough-cut capacity planning is a high-level check: do you have the capacity across your key resources to execute your master production schedule? It compares planned production load against available capacity at a broad level, helping you identify potential bottlenecks before they cause schedule failures.

Detailed Capacity Requirements Planning (CRP)

Detailed CRP goes further, calculating the specific load on each work center for each time period based on the MRP plan and the routings. This tells you whether any specific work center is overloaded in any specific week — and allows planners to level the load by adjusting production quantities or dates, or by adding capacity through overtime or outsourcing.

Quality Management Integration

Many ERP manufacturing modules integrate with quality management functionality, either as part of the same module or as a connected quality module. Key touchpoints include:

• Incoming inspection: Quality checks on received materials before they’re released to production
• In-process inspection: Quality checks at defined points in the routing during production
• Final inspection: Quality checks on finished goods before they’re moved to saleable inventory
• Non-conformance management: Tracking of defects, root cause analysis, and corrective actions
• Quality cost tracking: Recording the cost of quality events (scrap, rework, inspection time) against production orders

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Frequently Asked Questions

Does every ERP manufacturing module include both MRP and shop floor control? Not necessarily. Some ERP packages offer manufacturing capability in tiers — a basic tier that covers production orders and BOM management without full MRP planning, and an advanced tier that adds MRP, capacity planning, and shop floor control. When you’re evaluating vendors, clarify which capabilities are included in each licensing tier and what your specific business requires.

What is the difference between MRP and MPS (Master Production Schedule)? The master production schedule defines what you intend to produce — the planned output of your factory by item and time period. MRP works below the MPS, calculating the material requirements needed to execute the MPS. MPS drives MRP; without a valid MPS, MRP planning has nothing to plan against. In practice, maintaining a realistic MPS is one of the most important disciplines in manufacturing planning.

How does the ERP manufacturing module connect to the accounting module? Production order costs — material consumption valued at inventory cost, labor at standard or actual rates, overhead allocated based on defined rates — flow to the general ledger automatically. As materials are issued, inventory decreases and work-in-progress increases. When production orders are completed, WIP decreases and finished goods inventory increases. When goods are sold, cost of goods sold is recognized. These journal entries are generated automatically by the manufacturing module based on transaction activity.

What’s the difference between discrete manufacturing and process manufacturing in ERP? Discrete manufacturing produces distinct, countable units — a machine, a pump, a device. Each unit is identifiable and traceable. Process manufacturing produces batches of a continuous or blended product — chemicals, food, paint — where the output is measured in volume or weight rather than individual units. The BOM and routing concepts are similar, but process manufacturing uses formulas and recipes rather than traditional BOMs, and the inventory management of co-products, by-products, and yield variance requires different handling. Most ERP platforms support one mode more natively than the other, so this is an important fit question during evaluation.