Batch Size vs Lead Time and Setup Share Calculator
Large batches spread the setup over more pieces but make every piece wait for the whole batch. This calculator shows both sides of the trade-off so you can decide whether to cut setup or shrink the batch.
Your numbers
Your results
Simplified batch-and-queue model without waiting between operations. Real lead times are longer. The point is the trade-off between setup share and lead time.
Batch lead time (hours) vs batch size
Sweeps Batch size from 1 to 200, holding your other inputs fixed.
Review lot size rules in your ERP
An optional review of fixed order quantities and setup parameters against current performance.
Optional. The tool and every export work without this. No spam.
How to use it
Enter the number of operations a batch passes through, the setup time per operation and the run time per piece. Move the batch slider to see the setup share and the process lead time change. Then set the setup share you can accept and read the batch needed to reach it, together with the lead time that batch causes. The comparison shows what small batches would require in setup reduction.
The formulas
Operation time for a batch equals setup plus batch size times run time per piece. Setup share equals setup divided by that operation time. Batch-and-queue lead time without waiting equals the number of operations times the operation time, since every piece waits for the entire batch at each step. The batch for a target setup share s is setup times (1 minus s) divided by s times piece time. These relations are standard in lot sizing and lean flow analysis.
- Op time = setup + batch x piece time
- Setup share = setup / op time
- Lead time = ops x op time
- Batch for share s = setup x (1 - s) / (s x piece time)
Reading the result
With a 30 minute setup and 2 minutes per piece, getting setup under 10 percent needs a batch of about 270, which makes the batch take hours at every step. The way out is to reduce setup time, not to accept the big batch. The chart is linear in batch size, so every piece you remove from the batch cuts lead time at a steady rate. Combine with transfer batches or one-piece flow to cut lead time further.
Common mistakes
Treating setup as a fixed cost to be spread, rather than a problem to be removed, is the usual trap. Another is forgetting that queue time between operations adds to the figures here. Also check the ERP lot size policy: a fixed order quantity chosen years ago may still drive batch sizes long after the setup has improved. Review minimum order quantities and routing setup times together.
- Accepting setup as fixed
- Ignoring queue time
- Stale ERP lot sizes
- Optimizing batch for one operation only
Frequently Asked Questions
Why not just make big batches to minimize setups?
Big batches cut setup cost per piece but raise lead time, WIP and the cost of defects found late. Lean aims to reduce setup time so smaller batches become economical.
Does this include waiting between operations?
No. It shows only process time for a batch. Real lead time includes queues, which usually add much more, so use it to compare options rather than to predict a due date.
What is a transfer batch?
A quantity moved to the next operation before the whole production batch is done. Smaller transfer batches overlap operations and cut lead time without changing setup frequency.
How does this relate to EPEI?
EPEI sets the production cycle for all parts on a shared resource. This tool looks at one batch through several operations. Use both when choosing lot sizes.
Netray can help review lot size and setup parameters across your ERP item master so batch rules match what the floor can now achieve.
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