MRP (material requirements planning) is a method that takes the production plan, explodes each product's bill of materials and subtracts stock on hand and on order to work out which materials are needed, in what quantity and by which date. In short, it turns "will we have the parts?" from a guess into a calculation.
How materials get planned before MRP
In many small manufacturers, material planning lives in one buyer's head. Orders build up in a spreadsheet, the buyer walks the stores, decides the fasteners look low and rings the supplier. It works while the product range is narrow and that person is not on holiday.
Variety breaks it. The same sheet steel appears in three product structures in different quantities, and one product's sub-assembly is another's raw material. The line stops for want of a single gasket while the warehouse holds shelves of parts nobody has touched in years.
Shortages and excess stock look like opposite problems, but they share a root cause: requirements are estimated rather than calculated. MRP makes the calculation systematic. For the wider system it usually sits inside, see our ERP guide for SMEs.
What unplanned materials cost you
Shortages are paid for in idle lines, expedited freight and missed delivery dates. Excess is paid for in cash tied up on shelves, warehouse space, damage and obsolescence. The two often happen at the same time: too much of the wrong material, not enough of the right one.
Having MRP is not the same as trusting it. A 2025 Qlector study of production planning among leading Slovenian manufacturers found that every company interviewed planned in ERP and that MRP was universal, yet 50% still used manual methods such as spreadsheets or paper alongside ERP, and only 25% considered their planning very efficient. The pattern is familiar on the shop floor too: when planners doubt the MRP output, they redo the calculation in a side spreadsheet and the two plans drift apart.
According to TurkStat's Survey on ICT Usage in Enterprises 2025, 28.3% of Turkish enterprises with 10+ employees used ERP software, rising to 76.5% among firms with 250+ employees but only 23.6% among those with 10-49.
In other words, more than three quarters of Turkish firms with 10-49 employees do not use ERP, so material requirements there are usually worked out in separate lists and from personal experience. Implementing one carries its own risk too. Panorama Consulting's 2026 ERP Report found that more than a quarter of organisations went over budget and almost a quarter over schedule, and the MRP module is one of the most data-hungry parts of such a project.
How MRP material requirements planning works: three inputs, one calculation, three outputs
The logic is simple; the difficulty lies in the data. MRP runs on three inputs:
- Master production schedule (MPS): how many of each finished product will be made in each period, built from firm customer orders and the demand forecast.
- Bill of materials (BOM): which sub-assemblies and raw materials make up each product, in what quantities, often across several levels.
- Inventory records: stock on hand, open purchase orders, open works orders, lead times, lot-sizing rules and safety stock.
For every level the calculation follows the same sequence. Gross requirements are derived, stock on hand and scheduled receipts are netted off, the net requirement is rounded up to the lot-sizing rule, and the order is offset backwards by the lead time. A planned order at one level becomes the gross requirement for the level below.
The outputs are planned purchase orders, planned works orders and exception messages telling you to expedite, defer or cancel existing orders. How planned works orders are then followed on the shop floor is covered in our piece on work order tracking.
Worked example: 200 control panels
A panel builder must ship 200 electrical control panels in week 5. Each panel needs one steel enclosure and six terminal blocks, and final assembly takes a week. Enclosures are fabricated in-house in one week; terminal blocks are bought in with a three-week lead time and sold only in boxes of 500. There are 40 enclosures and 700 terminal blocks in stock, plus 300 blocks due in week 2.
- Assembly start: shipping in week 5 with a one-week assembly means components must be ready at the start of week 4.
- Gross requirements: 200 enclosures and 200 × 6 = 1,200 terminal blocks.
- Enclosures: 200 − 40 = 160 net. With a one-week fabrication time, the works order for 160 must start in week 3.
- Terminal blocks: 1,200 − 700 − 300 = 200 net. Rounded up to a full box, the order is 500, leaving 300 in stock afterwards.
- Order date: with a three-week lead time, the purchase order must go out in week 1, which is this week.
Two items are easy in a spreadsheet. Hundreds of items, multi-level structures and orders that change daily are not, and that is where a system earns its keep.
MRP, MRP II, ERP and APS compared
These terms are often used interchangeably, but each answers a different question:
| MRP | MRP II | ERP | APS | |
|---|---|---|---|---|
| Question answered | Which materials, how many, when? | Are materials and resources sufficient? | Is the whole business on one dataset? | Which job, on which machine, in what order? |
| Scope | Materials | Materials, capacity, cost | Finance, sales, stock, production, HR | Finite-capacity scheduling |
| Capacity assumption | Infinite | Rough-cut check | Depends on module | Finite, to the minute |
| Time bucket | Day or week | Week or month | All horizons | Hour or minute |
| Where it usually sits | ERP production module | ERP production module | Core business system | Separate layer on top of ERP |
Because MRP assumes infinite capacity, a job it declares "materials ready" may still have no slot on the bottleneck machine. Manufacturing capacity planning closes that gap at monthly level, and APS production scheduling closes it by the hour. The layer that captures what actually happened on the floor is explained in MES vs ERP.
Is your data ready for MRP? A readiness check
MRP output is only as reliable as its weakest input. Be honest when filling in this table:
| Data | Ready when | Common failure |
|---|---|---|
| Bills of materials | Current for all active products, scrap factors defined | Engineering changes not applied, substitutes not recorded |
| Stock accuracy | System-to-shelf variance measured through regular counts | Issues booked late, scrap never written off |
| Lead times | Per supplier, updated from actual deliveries | One default value entered years ago |
| Lot-sizing rules | Minimum order, pack multiples, safety stock defined | Everything lot-for-lot, buyers round up by hand |
| Master schedule | Orders and forecast in one place, frozen weekly | Sales and production working from different lists |
Stock accuracy matters most: if the system shows 200 but the shelf holds 150, MRP will not suggest an order. Barcode-based handheld stock counting and cycle counting expose that gap. To keep item and supplier records consistent across systems, our master data management guide offers a practical framework.
Six steps to put MRP into practice
- Narrow the scope. Start with the product family that stops the line most often or ties up the most working capital.
- Validate BOMs against the floor. Compare the engineering structure with what production actually consumes, then add scrap factors and approved substitutes.
- Count stock and book consumption in real time. If material leaves the store without being issued in the system, the calculation is wrong within a week.
- Derive lead times from reality. Measure order-to-receipt times for recent purchases and replace the defaults.
- Put demand in one place. Firm orders and forecast should feed a single master schedule; for make-to-stock lines, AI demand forecasting strengthens it.
- Run in parallel, then switch. Compare MRP suggestions with the buyer's manual plan for a few weeks, investigate every difference and retire the spreadsheet once trust is earned.
Most of these steps are about process and data, not software. Why so many implementations stumble is the subject of why ERP projects fail.
How we deliver MRP projects at Digital Bridge
Product structures and supply realities differ from plant to plant, so we begin with a requirements analysis and confirm the scope and phases in a written proposal. A typical project covers:
- Discovery and data audit. We review BOMs, stock variances and lead times on site and agree which product family will benefit from MRP first.
- MRP inside or alongside your ERP. If your system already has an MRP module, we make it work with accurate data; if not, we build material planning through our ERP development and integration service. We weigh packaged against bespoke using the criteria in custom vs off-the-shelf software.
- Real-time stock and consumption. Warehouse movements are captured through warehouse and inventory management (WMS), and line-side consumption and output through MES production management.
- Linking materials to capacity. Once materials are available, our production planning and APS solution decides which machine runs the job and when.
- Demand and integration. For make-to-stock lines we feed the master schedule with demand forecasting analytics, and connect supplier portals, e-commerce or EDI through our system integrations layer.
- Pilot. MRP and the manual plan run side by side on the chosen product family for a few weeks; we measure the differences, then widen the scope.
If your plan still lives in a workbook, read signs you have outgrown spreadsheets, or browse all our software development articles.
Next step
Count how many times the line stopped for missing material in the last three months, and total the value of stock that has not moved in six. Put those two figures side by side and the case for MRP becomes concrete. Get in touch and we will review your BOMs and stock data with you and agree where to start.