Manufacturing & IndustrialMRP Planning
Raw Material Requirements Calculator
Determine total gross material purchase requirements for production schedules including scrap allowances, safety stock buffers, and inventory on hand.
MRP Raw Material Requirement Schedule
Order Quantity to Buy
—
net requirement
PO Procurement Cost
—
order quantity × price
Gross Required
—
BOM + scrap allowance
Safety Buffer
—
reserve stock
Gross Material Purchase Formula
Purchase Quantity = [(Target Units × BOM Spec) × (1 + Scrap %)] × (1 + Safety Stock %) - Stock On Hand- Net Requirement: Theoretical bill of materials needed for 100% perfect yield.
- Scrap Allowance: Anticipated manufacturing loss based on historical line scrap rates.
- Safety Stock: Buffer stock protecting against supply chain disruptions and delivery delays.
Step-by-Step Worked Example
Scenario: Planning resin requirements for 1,000 molded automotive housings
Calculation Steps:
- Net Material = 1,000 × 3.5 = 3,500 lbs
- Scrap Allowance (4%) = 3,500 × 0.04 = 140 lbs (Gross 3,640 lbs)
- Safety Buffer (10%) = 3,640 × 0.10 = 364 lbs (Total 4,004 lbs)
- Net to Purchase = 4,004 lbs - 1,000 lbs on hand = 3,004 lbs
- Estimated Purchase Order Cost = 3,004 lbs × $2.50 = $7,510
Result: Requires purchasing 3,004 lbs of raw material ($7,510) to fulfill the 1,000-unit run with scrap and safety buffers.
How to Use This Calculator
- 1Enter planned finished goods production target.
- 2Specify bill of materials (BOM) material requirement per unit.
- 3Input anticipated scrap rate percentage and safety stock buffer.
- 4Enter existing usable inventory on hand to get net purchase order volume.
Assumptions & Limitations
- On-hand inventory meets current engineering quality specifications.
- Unit of measure is identical between BOM specification and purchase orders.
Frequently Asked Questions
Why include both scrap allowance and safety stock?
Scrap allowance accounts for normal, expected in-process material loss during manufacturing. Safety stock buffers against unforeseen supplier delivery delays or sudden surge orders.
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