Minutes at the Station, Hours on the Shift Plan
A production line is timed in minutes. Somebody stands at a station with a stopwatch, records how long one unit takes from the moment work starts to the moment the piece leaves, and writes down something like 4.8. Everything that happens to that number afterwards is counted in hours: the shift is eight of them, the labour rate is per hour, capacity is quoted per hour and the planner's spreadsheet has no column for minutes at all. The conversion sits between the person who measured the work and the person who has to resource it.
What the Minute Figure Is Actually Measuring
Cycle time is what the process does
Takt time is what demand asks for
Labour content is a third number
Changeovers do not divide by the batch
Turning a Stopwatch Reading Into Shift Hours
The sequence below is the one a line supervisor runs after a time study, when the question stops being "how fast is this station" and becomes "how many hours does the order need".
Enter the minutes for the whole order, not for one unit
Multiply the cycle by the quantity first — 4.8 by 250 gives 1 200 minutes — and type that in. Both fields accept a comma instead of a full stop, so a figure written 4,8 on a European time-study sheet needs no editing.
Multiply by the operators in the cell
Machine hours and labour hours are not the same bill. A cell staffed by two people consumes two labour hours for every hour the cell runs, and the costing sheet wants the second figure.
Add the setup once per run
Changeover minutes belong to the batch, not to the piece. Add the setup to the order total before converting, then check what it did: 45 minutes on a run of 100 adds 0.45 minutes to every unit.
Reverse it when the hours come first
Capacity planning usually runs the other way: you are handed 7.5 net hours and need the minutes to divide by. The swap button (↔) turns the page into h → min, and the copy control on each field hands over the bare number for a spreadsheet cell.
Cycle Times and the Hours They Consume per 100 Units
Typical station cycles from a mixed-manufacturing line, each shown as the minutes a stopwatch records and the hours a hundred pieces take off the schedule. The last row is deliberately different: it is charged once per run rather than once per unit.
| Operation | Cycle time per unit | Hours per 100 units | Note |
|---|---|---|---|
| Press stroke with take-out | 0.6 min | 1 h | Machine-paced; one operator tends two presses |
| Injection moulding, shot plus de-gate | 0.75 min | 1.25 h | Cooling dominates; the tool fixes the cycle |
| Robotic weld cell | 1.5 min | 2.5 h | Load and unload run parallel to the arc time |
| Final test and pack | 2.25 min | 3.75 h | Retests add minutes the standard never shows |
| CNC milling operation | 3.2 min | 5.33 h | Spindle time plus one load; usually the bottleneck |
| Manual assembly station | 4.8 min | 8 h | One operator, one shift, one hundred pieces |
| Tool changeover between variants | 45 min per run | 0.75 h per run | Charged once, whatever the batch size |
Read down the middle column and the bottleneck picks itself out: the milling operation at 3.2 minutes can feed an assembly station that only needs a piece every 4.8, but it will strangle a line running to a 3-minute takt. Read the right-hand column instead and the same data turns into a resourcing statement — the numbers a planner puts against a shift, a machine centre and a labour rate.
What This Pair Does During a Line-Balancing Session
Balance the line while the stopwatch is still warm
Type in either box and the other keeps pace, so station totals collected on the floor become shift hours at the whiteboard without leaving the conversation.
Work backwards from an hours budget
Swapping the pair answers the capacity question instead of the costing one: how many minutes 7.5 net hours really offers, and how many units that buys at today's cycle.
Days and weeks for the master schedule
Both dropdowns are searchable across every time unit the app defines, so a total of 12 000 assembly minutes can be read straight in days or weeks when the discussion moves up a level.
Hundredths of a minute survive the trip
Results keep up to eight decimals, so a 0.05-minute element from a work-measurement sheet still reads as 0.00083333 h instead of rounding away to nothing.
Questions From the Line-Balancing Review
Our cycle is 4.8 minutes and takt is 3 — how many stations does that need?
Divide the cycle by the takt: 4.8 ÷ 3 is 1.6, so two parallel stations, or one station whose work has been split between two operators. Two stations give an effective 2.4-minute cycle, comfortably inside takt, and the 0.6 minutes of slack per unit is what absorbs a jam or a piece that needs reworking. Rounding down to one station is not an option — a line running at 4.8 against a 3-minute demand loses 1.8 minutes on every unit, which over 100 units a day is three hours of shortfall that nothing in the plan ever gives back.
Why is the labour content per unit bigger than the cycle time?
Because the clock runs once and the people are counted individually. A 4.8-minute cycle with three operators inside it consumes 14.4 minutes of human work per piece, which is 0.24 labour hours; the station still produces one unit every 4.8 minutes. Costing sheets want the 0.24, capacity plans want the 4.8, and a great many arguments about "hours per unit" turn out to be two people quoting different numbers correctly. Say which one you mean before the figure goes into a quotation.
Do changeover minutes belong inside the cycle time?
No — a setup is charged once per run, so it never divides neatly into a per-unit figure. Keep it separate, then look at what it does to the average: 45 minutes spread over 100 pieces adds 0.45 minutes each, which on a 4.8-minute cycle is a 9 % penalty, while the same setup over a run of 1 000 adds only 0.045. That relationship is the whole argument for cutting changeover time instead of growing batches — a setup pulled down to single-digit minutes lets you run small batches without paying for them.
Which OEE bucket swallows the minutes between 480 and the hours we ran?
They disappear in three places. Breaks, meetings and planned maintenance come out before the measurement starts, taking a 480-minute shift down to a planned production time nearer 450. Breakdowns, waiting for material and changeovers then come out of availability. What remains is run time, and if the line produced fewer pieces than that run time allowed for, the gap is performance loss — small stops and slow running nobody wrote down. Scrap and rework land in quality. Convert each bucket to hours separately; a single figure for "lost hours" hides which of the three you should be fixing.
Should breaks come out before takt is calculated?
Always. Takt is net available time divided by demand, and net means the time the line can genuinely be running. Take two twenty-minute breaks and a ten-minute handover out of a 480-minute shift and 450 are left, or 7.5 hours. For 100 units that is a takt of 4.5 minutes rather than 4.8 — a 6 % tighter pace than the gross figure suggests, and precisely the gap that turns into overtime at the end of the week. The honest calculation looks pessimistic on paper and is the only one that survives contact with a real shift.
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