Production Run Economic Batch Size (EPQ) Calculator
Choosing a batch size too small floods the shop with setups, while too large ties up cash in stock. The economic production quantity gives a defensible starting point for lot size in your MRP.
Your numbers
Rate while the machine runs on this part, expressed per year.
Setup hours times machine rate plus scrap on first pieces.
Your results
Classic EPQ assumes steady demand and a constant setup cost. Constraints such as shelf life, machine minimums and material packs may override the result.
Economic batch size vs setup cost
Sweeps Cost per setup from 10 to 600, holding your other inputs fixed.
Check my item master lot sizes
Optional: have an expert compare your ERP lot sizes with calculated economic batches.
Optional. The tool and every export work without this. No spam.
How to use it
Enter annual demand and the rate at which the machine can produce that part. Cost per setup should include labor, machine time and scrap of first pieces. Use unit cost with your carrying rate to get the holding cost. Read the economic batch, then round to a practical size such as a full pallet, a material pack or a whole shift of output.
The formula
EPQ equals the square root of 2 times demand times setup cost, divided by holding cost per unit times one minus demand over production rate. The factor in the denominator reflects that stock builds up while production runs and is consumed at the same time, so the average inventory is lower than half of the batch.
- Higher setup cost pushes the batch up
- Higher unit cost or carrying rate pushes it down
- A production rate close to demand pushes it up sharply
- Total cost is flat near the optimum, so rounding is safe
Reading the result
Check runs per year and days between runs. If days between runs are shorter than your planning cycle, the part effectively runs continuously. The sweep chart shows why reducing setup time is powerful: halving setup cost reduces the economic batch by about 29 percent and cuts the work in process you carry.
Common mistakes
Teams use purchase price instead of manufactured cost, use only labor in setup cost, or leave capacity utilization above 100 percent which makes the formula meaningless. Another mistake is treating the result as law instead of a guide: respect minimums set by tooling or material packs.
Frequently Asked Questions
What is the difference between EOQ and EPQ?
EOQ assumes the whole order arrives at once, as with purchased parts. EPQ assumes stock builds gradually while you produce, which reduces average inventory and increases the economic quantity.
What setup cost should I use?
Include setup labor hours at the loaded rate, machine time at its hourly rate and scrap during setup. Leaving out machine time understates the cost, which leads to batches that are too small.
Why does capacity utilization matter?
If demand approaches production rate, the part nearly occupies the machine full time and the formula grows without bound. The calculator caps the factor at 1 percent, but you should treat any utilization above 85 percent as a capacity problem.
Should I use the result directly as lot size?
Use it as a starting point, then round to practical units. Because total cost is flat near the optimum, a 20 percent deviation changes annual cost by only a small amount.
Netray can compare these results with the lot sizes currently set in your ERP item master and flag the largest gaps.
Related Tools
Make to Order Promise Date and Lead Time Calculator
Compute the calendar days to promise a customer from material arrival, queue, setup, run hours at your efficiency, and ship time.
MES & Shop FloorWIP Cash Tied Up Calculator Using Little's Law
Estimate how much cash sits in work in process from output rate and flow time, and what a shorter flow time would release.
Costing & FinanceScrap Adjusted Product Cost and Price Calculator
Calculate cost per good unit after material scrap and process yield, then the selling price needed for a target gross margin.
ERP Migration & SelectionSmall Manufacturer ERP ROI and Payback Calculator
Estimate annual benefit, payback months and three year net for a cloud MRP or ERP at a small plant, with a what-if sweep on inventory reduction.
More Discrete Manufacturing tools
See all- OEE Calculator (Overall Equipment Effectiveness)
- Scrap Rate Cost Calculator
- Takt Time Calculator
- Cycle Time & Capacity Calculator
- Inventory Carrying Cost Calculator
- Economic Order Quantity (EOQ) Calculator
- MRP Nervousness Assessment
- Production Scheduling Maturity Assessment
- Shop Floor Digitization Scorecard