What is MRP (material requirements planning)?
Any business that builds a product from several components faces two questions: what to order or make, and when. Answering them by hand works until it does not. MRP is the calculation that answers both automatically. Here is what the acronym means, how a net requirement is computed, and why this logic sits at the core of every manufacturing ERP.
TL;DR, the essentials
- MRP stands for Material Requirements Planning. It is both a production-management method and the software module that runs it.
- It answers two questions: what to buy or manufacture, in what quantity, and by when, to fulfill a production plan.
- The calculation reads the bill of materials, turns gross requirements into net requirements by subtracting stock, then time-phases each order using lead times.
- The method evolved: MRP II adds machine and labor capacity, and DDMRP drives production from real demand rather than forecasts.
You run into MRP on an ERP feature list, in an industrial spec sheet, or in a conversation with an operations manager, and you want a straight answer. Here it is: MRP stands for Material Requirements Planning. Behind the acronym sits a very concrete calculation. From what you have committed to produce, MRP works out everything you must order and manufacture, and exactly when to release each order. Let us walk through the mechanics, the data it depends on, and its relationship with the ERP.
What does MRP mean, exactly?
MRP is short for Material Requirements Planning. The term covers two things at once: a method for planning production, and the software module that executes it inside an ERP or a dedicated manufacturing system.
The idea was born in 1960s manufacturing, when factories first computerized the calculation of their net requirements. The goal remains identical today: instead of ordering on gut feel or replenishing stock blindly, you derive requirements mathematically from what you plan to build. An MRP engine therefore answers two simple but critical questions, what to order or make, and when to release it, so the component lands just in time, neither too early (cash tied up in stock) nor too late (a shortage that halts the line).
In one sentence
MRP turns a production plan into a precise list of purchase and work orders, each one dated to arrive at the right moment.
How is a net requirement actually computed?
The heart of MRP is the move from a gross requirement to a net requirement. The gross requirement is the total quantity of a component needed to meet the plan. The net requirement is what actually remains to be ordered once you subtract what you already hold. Here is how the calculation unfolds, step by step, for a single component.
Compute the gross requirement
The system reads the bill of materials (the list of components and their quantities) and multiplies it by the master production schedule. Example: 100 bikes to assemble, 2 wheels each, so 200 wheels gross.
Subtract stock and open orders
You deduct on-hand inventory and orders already released. With 50 wheels in stock and 30 inbound from a supplier, the net requirement drops to 200 − 50 − 30 = 120 wheels to order.
Time-phase the order
MRP offsets the order date by the lead time. If wheels take 10 days and are needed on the 30th, the order must go out on the 20th. The calculation then cascades down to the next level of the bill of materials.
Where a spreadsheet quickly hits its limits (scattered data, manual math, versions that contradict each other), an MRP engine recalculates every net requirement in a single pass, all the way down the bill of materials. That ability to chain the levels, from finished product down to raw material, is what makes the method valuable. An intermediate component (a sub-assembly) becomes a gross requirement in turn for the parts that make it up.
Garbage in, garbage out
MRP is only as good as its data. An outdated bill of materials, a book stock that differs from the physical count, or a wrong supplier lead time, and the calculation produces wrong orders. Before you automate, clean up your inventories and your bills of materials.
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Quick quiz
How do you get the net requirement for a component?
What data does MRP need to run?
A requirements calculation only works on three reliable inputs. They are the foundations of the method, and often the real project work when you roll out MRP:
- The master production schedule (MPS): what you plan to build, in what quantity and by when. It blends firm orders and sales forecasts.
- The bills of materials: the detailed makeup of each product, raw materials and sub-assemblies included, with unit quantities. This is the master data of MRP.
- Inventory and open orders: the quantities actually on hand and the orders already released, so you can move from gross to net.
On top of these three pillars, a few parameters sharpen the result: lead times (purchasing or manufacturing) for time-phasing, lot sizes (you rarely order one unit at a time), and a safety stock that absorbs demand or delivery variability. This direct dependence on stock is why MRP is never designed in isolation: it rests on solid inventory management, itself wired to purchasing and the supply chain.
MRP, MRP II, DDMRP: what is the difference?
The method has changed a lot in sixty years. Three generations coexist today, and it helps to tell them apart before you compare software:
- MRP (or MRP 1): the material requirements calculation on its own. It answers the “what” and the “when”, but implicitly assumes you will always have the capacity to build.
- MRP II (Manufacturing Resource Planning): the major evolution, which adds capacity (machines, labor) and the financial dimension. The plan then reflects not just the materials needed but whether you actually have the hours to build them. MRP II is the direct ancestor of the modern ERP and remains the backbone of most production modules.
- DDMRP (Demand Driven MRP): formalized by Carol Ptak and Chad Smith at the Demand Driven Institute, this more recent model drives production from real demand rather than forecasts. It combines principles from MRP, lean and the theory of constraints, placing stock buffers at strategic decoupling points. The aim is more responsiveness and smoother flow, a concern that recent supply shocks brought back to the front.
Good habit
Do not pick an acronym, pick a need. Most small and mid-sized manufacturers are well served by a solid MRP II built into the ERP. DDMRP earns its keep on long, volatile, multi-echelon chains.
How does MRP relate to an ERP?
MRP never lives in a vacuum: it depends on inventory, purchasing, sales and accounting. That is why it is most often offered as a module of an ERP, the software that centralizes the whole business in a single database. The payoff is direct: when a work order consumes materials, inventory decrements and the purchasing module fires a replenishment, with no re-keying. If the concept is new to you, our primer on what an ERP actually is lays out the full picture, and our piece on production planning puts MRP back into the wider set of shop-floor methods.
Two approaches coexist on the market:
- The production module of a general-purpose ERP (Odoo, ERPNext, Microsoft Dynamics 365 Business Central, SAP, NetSuite): MRP is one brick among many, natively connected to inventory, purchasing and accounting. Ideal when you want a single tool for the whole company.
- A dedicated MRP or MES tool: more specialized for demanding industrial needs (fine scheduling, advanced shop-floor execution). It then interfaces with the ERP for the management side. A fit for manufacturers with complex processes.
On pricing, open-source ERPs concentrate most of the searches. Odoo ships a full Manufacturing (MRP) app, with a One App Free plan limited to a single app, then a Standard plan around $24.90 per user/month billed annually that unlocks every app (indicative US pricing, July 2026, check odoo.com/pricing since Odoo adjusts rates once or twice a year). ERPNext is free when self-hosted under GPL, with managed Frappe Cloud from around $5/month. Microsoft Dynamics 365 Business Central lists $80 per user/month for Essentials and $110 for Premium (the Premium tier is the one that adds manufacturing and MRP; indicative US pricing after Microsoft’s November 2025 increase, July 2026), while SAP Business One and NetSuite stay on a custom quote through an integrator. The integration line (setup, migrating bills of materials, training) often weighs more than the license itself.
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Your next step
To go further, read our best ERP software 2026 comparison, our explainer on production planning, or our guide to inventory management, the function directly wired to MRP.
Frequently asked questions
What does MRP stand for?
MRP stands for Material Requirements Planning. It refers both to a production-management method and to the software module that runs it. Its job is to determine what to buy or manufacture, in what quantity and by when, in order to fulfill a production plan.
What is the difference between gross and net requirements?
The gross requirement is the total quantity of a component needed to meet the production plan, derived from the bill of materials. The net requirement is what actually remains to be ordered or made once you subtract on-hand stock and orders already released (open orders). It is the net requirement, not the gross, that triggers a purchase or work order.
What is the difference between MRP and MRP II?
MRP (or MRP 1) calculates net material requirements from demand and bills of materials: it answers the what and the when. MRP II (Manufacturing Resource Planning) extends it by adding machine and labor capacity plus the financial dimension, so the plan reflects whether you actually have the hours to build what you scheduled. MRP II is the direct ancestor of the ERP and remains the core of most production modules.
What is DDMRP?
DDMRP (Demand Driven MRP) is an evolution formalized by Carol Ptak and Chad Smith of the Demand Driven Institute. Instead of driving production from forecasts, it relies on real demand and positions stock buffers at strategic decoupling points. It blends principles from MRP, lean and the theory of constraints to gain responsiveness and dampen supply swings.
Do you need an ERP or a dedicated MRP tool?
It depends on the complexity of your processes. For most small and mid-sized manufacturers, the production module of a general-purpose ERP (Odoo, ERPNext, Dynamics 365 Business Central, SAP, NetSuite) is enough, with the advantage of being natively connected to inventory, purchasing and accounting. Manufacturers with demanding needs, such as fine scheduling or advanced shop-floor execution, may prefer a dedicated MRP or MES tool interfaced with the ERP. Either way, integration with the rest of the business is the deciding factor.