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In-plant milk run: material handler route

Find out how many containers each round carries, whether one handler can hold the cycle, how many carts to buy and how much stock to keep at each station.

Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.

Pre-sizingRevised 11/02/2026
Route
Tugger and carts
Line-side stock
Points of use
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One station per row, in route order. Weight is optional (leave it blank to skip the train load check).

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—Handlers (tuggers) needed
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Handler route by station

Containers per round (average and on the heaviest round), weight and minimum stock to keep at each station.

Round time vs cycle

Breakdown of one round’s time (on the heaviest round), compared with the cycle and the maximum utilization.

Tap the chart to see the values.

Choosing the cycle: utilization vs line-side stock

For each possible cycle: handler utilization (bars) and containers kept at the stations (line).

Tap the chart to see the values.

Next step

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Method, assumptions and references

Equations used

Containers per round (average) = usage/h × cycle ÷ 60 ÷ parts per container; heaviest round = ⌈average⌉ (at least 1)
Round time = length ÷ speed + number of stations × time per stop + containers × time per container + supermarket time
Handlers = max(⌈round time ÷ (cycle × max utilization)⌉; ⌈containers ÷ (containers per cart × carts per train)⌉; ⌈weight ÷ load limit⌉)
Carts = trains × ⌈containers per train ÷ containers per cart⌉ × sets
Minimum line-side stock = ⌈usage/h × cycle ÷ 60 × cycles to replenish × (1 + safety) ÷ parts per container⌉ containers

Assumptions and limits

  • Fixed-cycle route: the handler visits every station each round, delivering according to the cards collected.
  • The round is sized for the heaviest one (each station rounded up); usage is constant over the shift.
  • With more than one handler, stations are assumed split into routes of similar load.
  • Handler breaks are not modeled (they are covered by maximum utilization), nor crossings and forklift traffic.

Standards and technical documents

  • Harris, R.; Harris, C.; Wilson, E. Making Materials Flow. Lean Enterprise Institute, 2003
  • Baudin, M. Lean Logistics: The Nuts and Bolts of Delivering Materials and Goods. Productivity Press, 2004
  • Smalley, A. Creating Level Pull. Lean Enterprise Institute, 2004
  • Droste, M.; Deuse, J. A planning approach for in-plant milk run processes to optimize material provision in assembly systems. Proceedings of CARV, 2011
  • Tompkins, J. A. et al. Facilities Planning, 4th ed. Wiley, 2010

U.S. regulations

  • OSHA 29 CFR 1910.178: Powered industrial trucks (tuggers and tow tractors)
  • OSHA 29 CFR 1910.176: Handling materials, general
  • ANSI/ITSDF B56.9: Operator controlled industrial tow tractors
  • NIOSH Revised Lifting Equation (manual handling of containers)

Frequently asked questions

What is an in-plant milk run?

It is a fixed route on which a material handler (also called mizusumashi or water spider) leaves the supermarket, visits every station on a regular schedule, delivers full containers and collects empties or kanban cards. It replaces on-call forklift trips with small, frequent deliveries and less line-side stock.

How do I choose the route cycle?

The cycle is the interval between two visits to the same station. A short cycle cuts line-side stock but needs more rounds. In the example, at 30 min the round takes about 14 min (47% of one handler); the cycle chart shows that 20 min would still fit one handler (67%), with 17 containers at the stations instead of 24.

Where does each station’s hourly usage come from?

Multiply the product’s hourly output by the part quantity in the bill of materials, adding up all products that use the same part. If output varies, use the busiest hour of the shift, or the calculator will undersize the round.

How do I measure stop and handling times?

Follow a few real rounds with a stopwatch: time to stop and pull away at each station, and time to swap each container (take the full one, place it, collect the empty). With gravity racks and small bins, 8 to 15 s per container is common; the example uses 12 s.

Why does line-side stock use 2 cycles?

Because in the most common routine the card from a used container is collected on one round and the full container arrives on the next. Meanwhile the station keeps using parts. In the example, Assembly A uses 120 parts per hour: 2 cycles of 30 min plus 20% safety give 144 parts, or 4 containers of 40.

How many carts should I buy?

Each train needs one round’s carts times the number of sets: one on the road and one being loaded at the supermarket. In the example, 12 containers per round on 8-container carts means 2 carts per train; with 2 sets, 4 carts.

What are the limits of this calculator?

It assumes constant usage, a visit to every station each round and a balanced split of stations when there is more than one handler. It ignores traffic, crossings and supermarket queues. For routes with many different parts, check the cart’s physical space and tugger safety rules (OSHA 1910.178).