MRP — Material Requirements Planning

Material Requirements Planning (MRP) is the classic procurement and production-planning routine inside an ERP system. From the sales plan and the bill of materials, MRP derives net requirements per item: which materials need to be ordered or produced, in what quantities, and by when. The newer extension MRP II adds capacity planning; APS (Advanced Planning & Scheduling) goes beyond infinite-capacity assumptions and resolves bottlenecks finitely.

MRP logic in four steps

Gross requirements: derived from the production plan plus forecast or open sales orders
Net requirements: gross minus available stock and minus existing open purchase or production orders
Lot sizing: per the configured policy (lot-for-lot, fixed order quantity, period-of-supply, EOQ)
Order proposals: scheduled-back by lead time, output as purchase or production order suggestions

Master data prerequisites

MRP only works as well as its master data. Critical fields per item: lead time, safety stock, lot-size policy, BOM structure with valid component allocations, and routing for in-house production. Many failed MRP projects trace back to inconsistent or out-of-date master data rather than ERP-tool shortcomings.

Practical example: the nightly MRP run

A mechanical engineering company runs its ERP nightly MRP automated: the system walks every open order, explodes each bill of materials to component level, calculates gross demand per material, subtracts available stock and determines net requirement including replenishment lead time. Each morning, 80-150 purchase suggestions await approval; the buyer reviews, consolidates where useful and releases to suppliers. Before MRP automation, the buyer needed 4-5 hours daily for the same task; now 30-60 minutes of validation.

Common pitfalls

MRP runs daily or weekly and is computationally heavy — for large product catalogues with several BOM levels, run times of several hours are not unusual. Variant-rich production benefits from a separate APS layer that resolves capacity bottlenecks.

Frequently Asked Questions

Is MRP the same as MRP II?

No. Classic MRP only schedules material requirements assuming infinite capacity. MRP II adds finite-capacity checking and integrates production with financial and HR planning. Most modern ERP systems implement MRP II as default, even though the abbreviation MRP is still used colloquially.

Do I need APS in addition to MRP?

If your production runs at near-100% capacity, has multiple competing bottleneck resources, or requires sequence-dependent setup times, an APS layer pays off. For simple assemblies with abundant capacity, the ERP's native MRP suffices.

Which ERP systems implement MRP best?

SAP S/4HANA, abas ERP, proALPHA, IFS Cloud, Microsoft Dynamics 365 Finance & Operations and Infor M3 all have strong MRP implementations. Cloud-native SMB tools like weclapp and Xentral cover MRP as a module — sufficient for assembly operations but limited for variant-rich manufacturing.