§ 15
How long does a job wait on average, and how much can be in progress at most?
Answer: Little's Law says average throughput time equals amount of work in progress (WIP) divided by how much is finished per time unit. It applies to a warehouse, a case stack, a laundry or an inbox with complaints. The law explains why in Lean you reduce throughput time by limiting work in progress and not just by working faster. You count yourself what is in progress and how much is finished per day. The calculator gives throughput time and the WIP ceiling needed to reach your goal.
Gennemløbstid (W) = igangværende arbejde (L) ÷ gennemstrømning (λ), altså L = λ × W
WIP-loft = gennemstrømning × mål for gennemløbstid
Use the same unit throughout: pcs and pcs per working day gives days
| Symbol | Meaning | Unit |
|---|---|---|
| wip | Work in progress right now (WIP) | stk |
| gennemstroemning | Finished per working day (throughput) | stk/dag |
| timer_pr_dag | Working hours per day | timer |
| maal_dage | Target for throughput time | dage |
| = | Average lead time | dage |
| = | Lead time in working hours | timer |
| = | WIP ceiling to reach the target | stk |
| = | Work in progress that needs to leave the system | stk |
Does not apply when
The calculator's own default values inserted. The figures are calculated with exactly the formula the tool uses.
Substituted
Giver
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Når kunderne klager over, at det tager for lang tid, er det fristende at bede folk arbejde hurtigere. Little's lov viser, at gennemløbstiden også afhænger af, hvor meget der står i gang. Du bruger den i værdistrømsanalysen og på tavlemødet, når I skal sætte et loft over igangværende arbejde.
Kundeservice har 120 åbne reklamationer, og teamet lukker 30 om dagen. Ledelsen vil have dem lukket på to dage.
It means: En reklamation venter i gennemsnit 4 days. For at nå to dage må der højst stå 60 pcs åbne, altså 60 pcs mindre end nu.
I en produktion står 450 halvfabrikata mellem maskinerne. Montagen gør 150 færdige om dagen, og målet er én dags gennemløb.
It means: Gennemløbstiden er 3 days, eller 22.2 hours. For at nå én dag skal lageret mellem maskinerne ned på 150 pcs.
I en sterilcentral står 80 instrumentsæt i kø, og der bliver gjort 40 færdige pr. dag. Afdelingerne vil have deres sæt tilbage dagen efter.
It means: Et sæt er 2 days undervejs. Med 40 pcs i kø ville målet holde.
Halverer I det igangværende arbejde med samme tempo, halveres gennemløbstiden.
Gennemløbstid × gennemstrømning skal give WIP.