A bearing is small enough to overlook on a spreadsheet and important enough to stop a production order. A UK manufacturer can have steel, labour, machine time, and a confirmed customer delivery date, yet still lose output because one component was ordered from instinct rather than calculated from the production plan.
That is the practical reason manufacturers ask what is material requirement planning. MRP turns demand for finished products into a dated plan for the components, materials, purchase orders, and manufacturing orders needed to build them. Inside an ERP such as Odoo, it works best as an exception-driven control layer, not as a blind reorder button. It shows the planner where supply, demand, timing, and cash are moving out of alignment.
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What Material Requirement Planning Actually Solves
A West Midlands contract manufacturer schedules an assembly run around a customer commitment. The team has most of the required parts in stock, but one bearing is missing. The buyer relies on experience, the supplier delivers three days after the required date, and the line loses two days of output while the team waits.
The bearing's demand didn't exist independently. Nobody decided to buy it because a forecast said “sell bearings”. It was needed because the manufacturer planned to build a finished assembly. This is dependent demand, where the requirement for a component comes from the requirement for its parent product. Finished goods, by contrast, usually have independent demand, driven by customer orders or forecasts.
The three questions a planner needs answered
Material Requirements Planning, or MRP, calculates material acquisition plans for purchase and manufacturing orders needed to meet production and customer demand. The Cambridge Institute for Manufacturing's explanation of MRP identifies dependent demand as the central problem. A finished-product requirement must be translated into the quantities of components needed at each level of the product structure.
A planner needs three answers:
- What materials and components are required?
- How many are required after considering available supply?
- When must each item arrive or be made?
That last question separates MRP from a simple stock list. The system creates a time-phased plan, so a component isn't merely marked as low. It's connected to the production date, its lead time, and the action needed to make it available.
MRP was formalised during the 1960s to address dependent-demand planning. In the UK context, Rolls-Royce and General Electric used computerised MRP concepts in the early 1950s, and the approach had reached 700 companies by 1975 and about 8,000 by 1981, as recorded in the history of material requirements planning. The important shift was from manual reorder methods to computer-based bill-of-materials calculations.
Practical rule: If a component is required because a parent product is scheduled, calculate it from the parent schedule rather than treating it like an unrelated consumable.
The Core Concepts Behind Every MRP Run
An MRP calculation needs reliable inputs. I explain them to manufacturing teams as four everyday objects: the recipe, the order book, the cupboard, and the delivery clock. Each answers a different part of the planning problem.
The recipe and the order book
The recipe is the bill of materials, or BoM. It lists the components and quantities needed to produce or repair a product. In Odoo, a BoM can act as the blueprint for a manufactured product or kit and can include operations and step-by-step production guidance, as described in the Odoo BoM documentation.
The order book is the master production schedule, or MPS. It states which finished products the business expects to make, and when. A sales order can create demand, while a forecast can shape the broader production plan. The MPS gives MRP the parent-level demand from which it can calculate component demand. A useful guide to building and managing an MPS is available in this master production schedule resource.
Think of the BoM as the recipe and the MPS as tonight's bookings. The kitchen can't calculate ingredients from the recipe alone. It needs to know how many meals are expected and when they're due.
The cupboard and the delivery clock
The cupboard is your inventory position. MRP needs to know what is physically available, what has already been allocated, what is due on open purchase orders, and what is expected from existing work orders. Gross demand becomes a smaller net requirement when usable supply is already available.
The delivery clock is lead time. Maintain supplier lead times separately from internal manufacturing and work-centre timing, because a purchased item and a made item don't move through the business in the same way. A safety lead time can protect a commitment, but it should be treated as a deliberate planning policy rather than a substitute for accurate supplier data.
MRP performs demand explosion by expanding a finished product into its subassemblies and parts. It then performs gross-to-net netting, subtracting on-hand stock and incoming supply from gross requirements before proposing new actions. Odoo describes the practical process as monitoring materials, identifying replenishment needs, and scheduling purchasing and manufacturing activities, including Purchase Orders, Manufacturing Orders, and Work Orders, in its MRP overview.
Safety stock is a buffer against variability in demand or supply. It won't correct a wrong BoM, inaccurate stock balance, duplicated supplier record, or outdated lead time. If those inputs are unreliable, the MRP run can produce a neat-looking plan that is operationally wrong.
MRP vs Reorder Points vs MRP II
A reorder point triggers replenishment when available stock falls below a defined level. That rule suits independent-demand items, such as packaging, cleaning materials, and standard consumables. It becomes less reliable for a product built through several assembly levels, because each component is needed according to the parent product's planned production date.
MRP coordinates those dependent requirements. It starts with the scheduled finished product, expands its BoM, checks existing stock and incoming supply, then dates the remaining requirement against lead times. In Odoo, this makes MRP an exception-driven control layer rather than a simple reorder rule. Planners can focus on shortages, date conflicts, and questionable inputs instead of reviewing every item manually.
The trade-off is data discipline. An incorrect BoM, stock balance, open order, or supplier lead time can produce a tidy recommendation that is wrong in practice. UK manufacturers dealing with variable lead times and working-capital pressure need to review those exceptions before approving purchasing or manufacturing actions.
MRP II extends the materials calculation into broader manufacturing resource planning. It considers capacity, shop-floor feedback, workforce requirements, and financial planning alongside material demand. Modern ERP platforms often provide parts of this model through connected modules, rather than presenting MRP II as a separate product.
| Criterion | Reorder Point | MRP | MRP II |
|---|---|---|---|
| Trigger logic | Stock crosses a minimum or replenishment level | Parent demand creates time-phased component requirements | Material demand is assessed alongside capacity, production, and financial constraints |
| Data needs | Stock levels, replenishment settings, and basic supply information | BoMs, production demand, inventory, open supply, and lead times | MRP data plus capacity, shop-floor, workforce, and financial information |
| Complex assemblies | Weak fit because it doesn't see the parent schedule | Strong fit for multi-level dependent demand | Strong fit where materials and capacity must be planned together |
| Future gaps | Shows a replenishment trigger | Shows dated shortages and planned actions | Shows material gaps alongside wider resource constraints |
| Best UK SME use | Independent consumables and straightforward stock items | Manufactured products with component relationships | Businesses managing capacity bottlenecks as well as materials |
Choose reorder points for independent consumables and straightforward stock items. Choose MRP when component demand follows a multi-level production plan. Examine MRP II capabilities inside the ERP when machine time, labour availability, material supply, and financial limits affect one another. The distinction between a manufacturing planning function and a wider ERP platform is also explained in this ERP versus MRP comparison.
How an MRP Workflow Runs Step by Step
Consider a finished chair in Odoo Manufacturing. Its BoM contains legs, dowels, and upholstery. Some parts are bought, while others may be made or processed internally. The MRP workflow turns the chair schedule into a set of dated supply decisions.
1. Demand explodes through the BoM
The run starts with demand for the finished chair, drawn from confirmed sales orders, forecasts, or the master production schedule. Odoo expands the multi-level BoM, moving from the finished chair to its subassemblies and then to the individual parts.
This is not a guess about how many legs the factory usually consumes. It's a calculation based on the quantity and structure of the scheduled parent product.
2. Net requirements are calculated
Odoo checks current stock, allocated stock, incoming purchase orders, and confirmed or in-progress manufacturing orders. Existing supply reduces the gross requirement. Only the remaining shortfall becomes a proposed replenishment need.
Stock accuracy matters. A quantity sitting in the wrong location, already reserved for another order, or recorded in the wrong unit of measure can distort the recommendation.
3. Dates are offset by lead time
The system works backwards from the required production or delivery date. A bought-in upholstery component is scheduled against its supplier lead time. A made part is scheduled against its internal manufacturing and work-centre timing.
If the lead time is too short, the recommendation arrives too late. If it's too long, the system may propose premature purchasing and tie up cash earlier than necessary.
4. Recommendations become actions
Odoo separates bought parts from made parts. A purchased component can generate a suggested Purchase Order or RFQ, while an internally produced item can generate a Manufacturing Order and related Work Orders. Replenishment rules determine how the planner sees and releases these proposals.
For a deeper operational treatment of BoM structure, see this Odoo bills of materials guide for manufacturers.
5. Existing orders are rescheduled
An MRP run doesn't only create new recommendations. If the required date changes, it can flag existing orders that now arrive too early, too late, or in the wrong quantity. The planner reviews those exception messages and decides whether to expedite, postpone, split, cancel, or leave the order unchanged.
That review is the human control point. The scheduler provides signals. It doesn't understand every commercial promise, supplier relationship, or production risk without the planner's judgement.
Benefits, KPIs, and the Trade-offs Nobody Mentions
MRP earns its place when it helps a planner act earlier and with better context. It can expose a component shortage before production reaches the affected operation, consolidate related purchasing needs, reduce manual checking across product records, and identify stock that no longer supports a credible demand signal.
The benefits should be measured through operating behaviour rather than vague claims about efficiency. Track whether planned orders are released when expected, whether production follows the schedule, and whether inventory supports customer commitments without expanding unchecked.
KPIs that make the system accountable
| KPI | Formula | Year-one target |
|---|---|---|
| On-time in-full delivery | Orders delivered by the promised date and in the promised quantity ÷ total orders | Set a baseline, then improve it through agreed service-level goals |
| Planned order release adherence | Planned orders released on or before the required release date ÷ planned orders due for release | Define an internal target after measuring current planner behaviour |
| Safety stock coverage days | Usable safety-stock quantity ÷ average daily demand | Set by product criticality and service-level policy |
| Schedule adherence | Production completed to the approved schedule ÷ scheduled production | Establish a baseline by work centre or product family |
| Stock turn | Usage or cost of goods issued ÷ average inventory value | Improve without weakening the agreed service level |
The table deliberately avoids universal targets. A contract manufacturer, make-to-order engineering business, and stock-led producer have different service commitments, lead times, and cash constraints. Your first job is to establish trustworthy baselines and then set targets that reflect the commercial model.
The costs behind the promise
MRP only works when the BoM and inventory records are clean. A wrong component quantity can create a cascade of false planned orders, while an unrecorded receipt can make the system propose stock that the warehouse already holds.
UK businesses also face a difficult balance between resilience and working capital. Recent UK coverage reports electronics and telecom manufacturers building stock tactically to protect service levels while lead times rose by five days quarter-on-quarter, as reported by Procurement Pro's UK electronics manufacturing coverage. Separately, UK manufacturing commentary reports producers buying more inventory in anticipation of orders while official production data remains uneven across industrial sectors, creating pressure between availability and cash, as discussed in UK manufacturing conditions for 2025.
Cash-flow check: A suggested purchase order is not automatically a good purchase order. Review its demand date, service value, supplier reliability, and effect on working capital before approval.
As SKU counts grow, exception messages multiply. Planners need a review rhythm, clear ownership, and permission to reject recommendations that don't make commercial sense. For teams managing product quality alongside production detail, Evright's Craftsmanship guide offers useful context on the care and process discipline that can sit behind a finished product.
How MRP Fits Inside an ERP Like Odoo
MRP is more useful when it lives inside the ERP rather than in a disconnected planning file. In Odoo, manufacturing, inventory, purchasing, sales, and accounting can share the records that drive the calculation. That reduces the delay between a changed customer order, a revised BoM, an updated receipt date, and the next planning decision.
Follow the data through Odoo
Odoo Manufacturing owns the BoM, operations, routings, Manufacturing Orders, and Work Orders. The production structure tells the system what must be made and how the work is expected to flow.
Odoo Inventory records stock locations, reservations, lots, replenishment rules, and movements. The replenishment dashboard gives the planner a working view of shortages and proposed actions instead of requiring a separate spreadsheet to reconcile stock.
Odoo Purchasing holds supplier data, RFQs, purchase orders, and expected receipt dates. Suggested RFQs can be reviewed against supplier commitments before the buyer releases them.
Odoo Accounting receives the financial effect of stock and purchasing movements. That connection helps finance teams assess inventory value, landed-cost movements, and margin implications without waiting for a manual export from manufacturing.
The practical touch points include the Manufacturing Orders list, the Master Production Schedule scheduler, the Inventory replenishment dashboard, and the Purchasing dashboard where suggested RFQs appear. A UK-focused overview of Odoo manufacturing for UK businesses describes how replenishment can consider confirmed sales orders, planned production, current stock, existing purchase orders, in-progress production, and minimum stock rules.
For smaller teams, good inventory management for SMBs depends on the same principle: keep purchasing, stock, and operational decisions connected to one current record. When a sales order or BoM changes, the planner can rerun MRP and review the new exceptions without copying data between systems. This guide to MRP in an ERP system explores that relationship in more detail.
Implementation Checklist and Common Pitfalls
Treat implementation as an operational audit, not a software installation. Before go-live, the operations lead should be able to sign off each planning assumption and explain which failure mode it prevents.
Audit the product and process model
- BoM accuracy: Confirm single-level and multi-level structures, phantom assemblies, quantities, revisions, and scrap assumptions. This prevents outdated product logic from generating cascading planned orders.
- Routing and work-centre capacity: Check operations, sequence, calendars, and available capacity. This prevents material plans from promising production that the shop floor cannot complete.
- Lead-time calibration: Compare supplier and internal lead times with actual operating experience. This prevents systematic late arrivals or unnecessarily early replenishment.
- Demand stability: Separate make-to-order products, forecast-led items, repeatable demand, and volatile demand. This prevents one planning policy from being applied across incompatible product families.
- Safety-stock policy: Set buffers according to service priorities and cash constraints. This prevents safety stock from becoming an unexamined working-capital increase.
- Supplier and unit-of-measure hygiene: Check supplier records, minimum quantities, purchasing units, conversion rules, and duplicate products. This prevents duplicate purchase suggestions and quantities that buyers can't place.
- User-acceptance testing: Run staged tests inside Odoo using representative products, receipts, sales orders, cancellations, substitutions, and date changes. This prevents a successful demonstration from hiding a failed daily workflow.
The order of testing matters. Start with one product family, follow demand into stock and purchase planning, then test exceptions such as a delayed receipt or changed customer date. Ask users to explain why Odoo generated each proposal, not merely whether the screen looks correct.
Govern the run after launch
Go-live isn't the end of implementation. Agree how often planners review exceptions, who owns supplier-date changes, how BoM changes are approved, and which KPIs are reviewed by management. A planner should be able to distinguish a genuine shortage from a data error without manually investigating every line.
The safest MRP rollout is controlled, visible, and reversible. Change one planning rule, observe its effect, and document the decision before changing the next.
Keep change control tight around BoMs, lead times, safety stock, and replenishment rules. Without that discipline, users will lose trust in the recommendations and return to private spreadsheets, recreating the visibility problem the ERP was meant to solve.
Where AI and Customisation Take MRP Next
AI can improve MRP, but it can't rescue poor master data. A forecast trained on incomplete sales history won't make a weak master schedule reliable, and a dynamic lead-time model can't compensate for purchase orders that suppliers update only by email.
The useful applications are specific. Statistical forecasting can feed the master schedule. Supplier on-time-delivery history can support dynamic lead-time estimation. Computer-vision quality checks can trigger component quarantine when an inspection fails. Inside Odoo, automated exception prioritisation can help planners focus first on shortages that threaten a customer commitment or critical operation.
Customisation with a purpose
Configurable reorder rules remain useful for independent-demand items. Multi-warehouse BoM substitution rules can help a planner use an approved alternative when the normal component is unavailable. Planner-by-product allocation can divide a large SKU portfolio between responsible users, so exception review has clear ownership.
These changes should make a decision easier to govern, not add more automation. An AI feature that produces a recommendation without showing the demand, supply, timing, and rule behind it can make an already uncertain plan harder to trust.
The same caution applies to capacity-constrained schedules. Probabilistic forecasts still need a human planner's sign-off when machines, labour, tooling, or customer priorities limit what the factory can produce. Claims of “autopilot” may describe rule-based automation under a new label, so ask what data the model uses, which decisions it can make, and how a planner can override it.
For teams assessing advanced Odoo workflows, machine learning consulting for Odoo ERP workflows can help frame those questions around a real process rather than a generic AI demonstration.
A sensible progression has three steps:
- Stabilise core MRP: Clean BoMs, stock records, supplier data, lead times, and exception ownership.
- Add one extension: Choose forecasting, supplier lead-time estimation, quality-triggered quarantine, or scheduling support.
- Measure before scaling: Compare service-level performance and inventory-turn movement against the baseline, then decide whether the extension deserves wider use.
The best MRP environment won't remove judgement from manufacturing. It will give planners earlier, clearer exceptions, so they can spend that judgement on the decisions that protect delivery, margin, and cash.
ERP Artists helps UK manufacturers configure Odoo Manufacturing and connect MRP with inventory, purchasing, accounting, integrations, training, and ongoing support. Visit ERP Artists to discuss an operational audit, an Odoo MRP rollout, or a focused customisation that makes your planning exceptions easier to act on.
