Calculator inputs
Example data table
Use these sample values to see a complete output.
| Orders | Lines/order | Pick sec/line | Scan sec/line | Travel m/line | Speed m/s | Pack sec/order | Pickers | Shift hrs | Util % | Cong % | Method | Batch | Zones | Error % | Rework sec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 240 | 6 | 12 | 3 | 8 | 1.20 | 18 | 6 | 8 | 80 | 10 | Batch | 8 | 2 | 1.0 | 60 |
Formula used
Pick lines: P = Orders × LinesPerOrder
Travel time per line: ttravel = DistancePerLine ÷ WalkingSpeed
Handling time: Thandle = (tpick + tscan) × P
Adjusted travel time: Ttravel = ttravel × P × TravelReduction(Batch) × ZoneReduction(Zones)
Packing time: Tpack = tpack × Orders
Rework time: Trework = P × ErrorRate × trework
Total time: T = (Thandle + Ttravel + Tpack) × CongestionMultiplier × MethodMultiplier + Trework
Labor hours: H = T ÷ 3600
Required pickers: PickersNeeded = ceil(H ÷ (ShiftHours × Utilization))
Notes: TravelReduction uses a capped logarithmic curve; ZoneReduction uses 1/√Zones. Replace these with measured site coefficients for higher accuracy.
How to use this calculator
- Enter planned orders and average lines per order for the shift.
- Set pick and scan seconds per line from time studies.
- Estimate average travel meters between picks and walking speed.
- Choose a picking method, batch size, and zone count.
- Include utilization, congestion, and error/rework assumptions.
- Click Optimize to view capacity, labor, and cost outputs.
- Use the scenario table to compare batch sizes quickly.
- Download CSV/PDF to share results with operations teams.
Throughput targets and line volume
A shift plan of 240 orders at 6 lines each produces 1,440 pick lines. If average handling is 15 seconds per line (12 pick + 3 scan), handling consumes 21,600 seconds, or 6.0 labor hours. At 6 pickers, 8 hours, and 80% utilization, available hours are 38.4, leaving room for travel, packing, and quality work.
Travel time as the dominant lever
With 8 meters between picks and 1.20 m/s walking speed, travel time is 6.67 seconds per line. Across 1,440 lines, baseline travel is 9,600 seconds (2.67 hours) before method, batching, zoning, and congestion adjustments. Reducing average distance by 20% saves about 32 minutes per shift at this volume.
Batching, zoning, and congestion impacts
The calculator uses a capped logarithmic travel reduction for batching and a 1/√Zones reduction for zoning. Moving from batch size 1 to 8 can lower modeled travel by roughly 25–40%, depending on your inputs. Two zones reduce travel by about 29% in the same model. A 10% congestion factor multiplies operational seconds by 1.10, often erasing small improvements.
Labor capacity and staffing decisions
Total labor hours H equals total seconds divided by 3,600, including rework. Required pickers are ceil(H ÷ (ShiftHours × Utilization)). If H is 44 hours and effective hours per picker are 6.4, staffing needs are ceil(44 ÷ 6.4) = 7 pickers. This framing makes overtime, cross-training, or temporary labor tradeoffs explicit.
Quality, errors, and hidden rework
Error rate is applied to pick lines, not orders. At 1.0% errors on 1,440 lines, you expect 14.4 errors. With 60 seconds rework each, rework adds 864 seconds (0.24 hours). Raising errors to 3% triples rework time and can also increase congestion through exception handling at pack stations.
Cost view and scenario comparison
Labor cost is H × hourly wage. At 44 hours and 12 per hour, cost is 528 for the shift. The scenario table tests multiple batch sizes while holding other parameters constant, highlighting a batch that minimizes required pickers and increases lines per labor hour. Use measured time-study data to calibrate coefficients for your facility. Track change weekly to sustain gains.
FAQs
What should I use for travel distance per line?
Start with a short time study: measure several pick sequences and divide total walking distance by lines picked. Use a weighted average by zone or SKU velocity for better accuracy.
How do I choose utilization?
Use paid time minus effective productive time. Many sites run 70–85% after breaks, meetings, and small delays. If utilization is uncertain, test a low and high value to see staffing sensitivity.
Does batching always improve performance?
Not always. Large batches can increase sorting, tote swaps, and exception time. Use the scenario table to compare labor hours and required pickers, then validate with a pilot on representative orders.
How should I model congestion?
Estimate the extra time caused by aisle blocking, queueing at docks, or pack-station backups. If congestion is seasonal, run separate scenarios for peak and off-peak shifts and compare utilization outcomes.
Why does zone count reduce travel in the model?
More zones shorten the average path a picker walks, but they can add handoff coordination. The calculator applies a simplified 1/√Zones reduction; adjust zones only if your process truly limits cross-zone walking.
Can I use this for multi-level mezzanines or lifts?
Yes, but include vertical travel as extra distance or add it to pick time per line. If lift waits are significant, reflect them in congestion or handling time to avoid understating labor hours.