ERP, MES, MRP and WMS: how do they differ?
ERP manages the business: orders, inventory, purchasing and finance. MRP calculates material needs inside or next to ERP. MES runs and records work on the shop floor. WMS runs work inside the warehouse.
Many products combine several of these, and one interface then serves users of all of them.
Key facts
- ERP answers what the business is doing and at what cost, over days to months.
- MRP answers what to buy or make and when, over weeks.
- MES answers what is running on the floor now, over minutes to shifts.
- WMS answers where stock is and who moves it, over minutes to days.
- In the ISA-95 model, ERP sits at level 4 (business planning and logistics) and MES at level 3 (manufacturing operations management).
The time horizons above are illustrative working contexts, not fixed boundaries between these systems or requirements of ISA-95. Planning horizons and product boundaries vary by implementation.
Comparison
| System | Main question | Main users | Time horizon |
|---|---|---|---|
| ERP | What is the business doing, and at what cost? | Managers, planners, finance | Days to months |
| MRP | What to buy or make, and when? | Planners | Weeks |
| MES | What is running on the floor now? | Operators, supervisors | Minutes to shifts |
| WMS | Where is the stock, and who moves it? | Warehouse staff | Minutes to days |
How they connect
ISA-95 describes manufacturing systems as levels. Level 4 covers business planning and logistics, including ERP. Level 3 covers manufacturing operations management, including MES. The standard deals mainly with the interface between these two levels.
In practice, ERP sends orders and plans down to MES, and MES sends back what was produced, consumed and scrapped. MRP runs on ERP data, and WMS exchanges stock movements with both. Each handover is a place where records can fall out of step.
The four systems serve people who work at different speeds, in different places, on different devices. A planner compares hundreds of records on two monitors. An operator records one step with gloves on. A warehouse worker confirms a location on a handheld. When one product covers several of these systems, each role still needs its own screens over the shared data.
Common mistakes
- Designing MES screens with ERP density
- Putting planning and execution on one screen
- Treating ERP inventory and WMS location stock as the same view
Where we’ve worked on this
- StartProto: manufacturing ERP and MES
- OnBatch: batch process ERP for beverage producers
- OATSystems: logistics app for warehouse workers
Sources: ISA, ISA-95 Standard: Enterprise-Control System Integration