The short answer
MRP (material requirements planning) is the calculation that decides what to make and buy; ERP (enterprise resource planning) is the broader system that runs the whole business — sales, purchase, inventory, production, accounting — with MRP as the planning module inside it. MRP is a brain; ERP is the body it sits in. You can run MRP on its own for planning, and many manufacturers do, but its output only becomes action when it is connected to the execution and procurement functions that ERP coordinates.
The confusion is understandable, because on a well-built platform the two are not separate products at all — MRP is simply the planning branch of one shared system. That single-platform vantage is the cleanest way to see the difference, and it is the argument a bolt-on MRP tool can never quite make. Start from the production planning pillar if you want the full picture; this page is the focused comparison.
What MRP is
MRP is a focused calculation. It takes demand — a sales plan or confirmed orders — explodes each finished good through its bill of materials, and nets every resulting requirement against stock on hand, open purchase orders, open work orders and reserved stock. Whatever is still short becomes a purchase requisition to buy or a work order to make. That is the entire remit: convert demand into a costed, netted, actionable plan. For the mechanics in detail, see what is MRP.
What MRP is not is a place to raise an invoice, post a payment, or run a sales pipeline. It is deliberately narrow — it plans. Its value is depth in one domain: multi-level BOM explosion, accurate netting, sensible split of buy versus make, and timing driven by lead times and reorder levels.
What ERP is
ERP is the wide system of record for a business. It ties together the transactional functions a manufacturer runs every day: sales and order acceptance, purchasing (PR → PO → GRN), inventory and stock movement, production and work-order execution, quality, dispatch and often accounting. Its strength is breadth and a single source of truth — one item master, one party master, one stock ledger that every function reads and writes.
ERP on its own, though, is mostly a recorder of what happened. It captures orders, receipts and issues, but the decision of what to plan — the netting, the explosion, the buy-versus-make split — is exactly the job MRP does. That is why MRP is almost always described as a module of ERP rather than an alternative to it.
MRP vs ERP, side by side
| Aspect | MRP | ERP |
|---|---|---|
| Scope | Planning: what to make and buy, and when | The whole business: sales, purchase, inventory, production, finance |
| Core job | Explode the BOM, net against stock and supply | Record and coordinate transactions across functions |
| Output | Purchase requisitions and work orders | Orders, POs, GRNs, invoices, stock ledgers, reports |
| Answers | “What should we do?” (a decision) | “What is happening?” (a record) |
| Depends on | BOM and live stock accuracy | Clean master data across every module |
| Relationship | MRP is normally a module inside ERP — the planning brain within the wider body | |
Where they overlap — and why bolt-on MRP struggles
The overlap is the data. MRP has to read the item master, the BOM and live stock; ERP owns those same tables. When MRP is a native module of the ERP, it reads them directly — no export, no interface, no reconciliation. When MRP is a separate bolt-on tool, it has to import a copy of the item master, BOM and stock from the ERP on a schedule, plan against that snapshot, then push suggestions back. Every one of those hops is a chance for the numbers to drift.
- A stock export taken this morning is already stale by the time MRP nets against it this afternoon.
- A BOM changed by an engineering note in the ERP may not reach the bolt-on planner until the next sync — so MRP plans on the old structure.
- Reserved stock and open work orders committed inside the ERP are invisible to an external planner, so it double-counts inventory.
- Two systems, two masters, and a reconciliation step that becomes someone’s weekly job — or someone’s weekly shortage.
This is the argument only a one-platform vendor can make: when planning reads the very same tables that execution writes, there is nothing to reconcile because there is only one version of the truth.
Which comes first?
For most manufacturers the honest sequence is: get the master data and inventory right first, then add planning. MRP cannot function without a correct multi-level BOM and accurate live stock — those usually live in the production and inventory functions that an ERP provides. So in practice the foundation (item master, BOM, stock, purchase, production execution) comes first, and MRP is switched on over the top of it.
The good news is that on a shared platform this is not a two-project decision. You do not buy an ERP, then buy an MRP, then integrate them. You license the planning branch of the same system whose inventory and production you already run — the BOM and stock are already there, and MRP simply starts reading them. If you are still on spreadsheets today, the practical first move is disciplined BOM and stock data; the planning engine pays off the moment that foundation is solid.
MRP as a module of one platform
Fast Planning is exactly this: the MRP / production-planning menu of one shared platform. Sold inside the full suite it is the planning module of Fast ERP; sold standalone it is the same engine with only the planning branch enabled, reading the same item master, BOM and stock tables that production and inventory use. Either way there is no interface between planning and execution, because they are not separate systems.
Not sure whether you need MRP, ERP, or both?
Tell us how you plan and execute today and we will show you the shortest path — often just switching on the planning branch over the inventory and production data you already have.
How Fast Planning fits both cases
Fast Planning Software serves the manufacturer who wants MRP over an existing foundation and the one buying the full suite. In both, the planning engine explodes the BOM, nets against live stock and open supply, and raises work orders and purchase requisitions that flow straight into Fast Production, Inventory and Purchase. Because it is one platform — the same tables, no data copy — the plan and its execution stay reconciled by construction. To go deeper on the planning side, read what is MRP and the production planning process; for the payoff in concrete terms, see benefits of production planning software.
Frequently asked questions
What is the difference between MRP and ERP?
MRP (material requirements planning) is a focused calculation that decides what to make and buy and how much, by exploding the BOM and netting demand against stock and open supply. ERP (enterprise resource planning) is the wider system that runs the whole business — sales, purchase, inventory, production and finance. MRP is normally a module inside ERP: the planning brain within the broader body. MRP answers ‘what should we do?’; ERP records ‘what is happening?’
Is MRP part of ERP?
Usually, yes. In most modern systems MRP is the production-planning module of a wider ERP, reading the same item master, BOM and stock tables the rest of the system uses. It can also run standalone as a dedicated planning tool, but then it must import a copy of that data from wherever it lives and reconcile suggestions back — which is why native MRP inside one platform avoids the interface and the drift.
Which should come first, MRP or ERP?
In practice the foundation comes first: a correct multi-level BOM and accurate live stock, which usually live in the inventory and production functions an ERP provides. MRP is then switched on over that foundation because it cannot net without accurate stock and BOM. On a shared platform this is not two projects — you enable the planning branch of the same system whose inventory and production you already run.
Can MRP work without ERP?
MRP can run as a standalone planning tool, but its suggestions only become action when connected to execution and procurement — the functions ERP coordinates. Standalone MRP has to import the item master, BOM and stock from elsewhere and push suggestions back, adding a reconciliation step. Native MRP inside one platform reads the live tables directly, so there is nothing to reconcile.
Why is bolt-on MRP harder than MRP inside one platform?
A bolt-on MRP tool keeps its own copy of the item master, BOM and stock, synced from the ERP on a schedule. Between syncs the copy drifts: stock is stale, a changed BOM has not arrived, and reserved stock or open work orders committed in the ERP are invisible, so the planner double-counts inventory. MRP inside one platform reads the same tables execution writes, so planning and execution share a single version of the truth.