Knitting Order Allocation, Machine Count & Slack to the Due Date
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Two machines is not half the time of one. Each brings its own changeover.
Machines Needed to Meet the Date
—
Smallest count that fits once each pays its changeover
Completion, Slack & Changeover Burden
Completion at the Allocated Count
—d
Slack to the Due Date
—d
Window Consumed
—%
Total Running Hours
—h
Hours Committed per Machine
—h
Slack per Machine
—h
Changeover Hours Paid
—h
Changeover Share of Committed Time
—%
Output at the Allocated Count
—kg/d
The model assumes every allocated machine is identical, available for the whole window, and runs at the stated rate throughout; where machines differ in diameter, gauge or feeder count the rates differ and quantity should be allocated in proportion to rate rather than evenly. The production rate should already include machine efficiency - it is kilograms actually delivered per running hour, not the geometric maximum. Changeover covers yarn change, cam and quality setting and first-piece approval, and it is paid in full by every machine regardless of how small its share of the order is. Running hours per day should be measured rather than taken from the shift pattern. Nothing here models yarn availability, which is the constraint that most often decides whether a knitting order actually starts on the day the plan says it does, nor the queue for a shared changeover crew.
Using this calculator
About the Knitting Order Allocation, Machine Count & Slack to the Due Date
The formula
This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.
The work, independent of how it is splitrunHours = orderKg / kgPerHour
Running time is a property of the order and the rate. Splitting it changes who does it and when, not how much there is.
Changeover comes out of the window firstmachinesNeeded = ceiling( runHours / ( dueDays x hoursPerDay - changeoverHours ) )
Each machine spends its changeover before it produces anything, so the time it can actually run is the window less that changeover. Dividing by the full window instead is the standard planning error and it under-allocates by one machine on tight jobs.
Splitting divides one term and not the otherhoursPerMachine = runHours / machinesAllocated + changeoverHours
This is why three machines do not finish in a third of the time. The running hours divide cleanly; the changeover is paid in full by every machine, and on short orders it dominates.
What the split costs in total capacitychangeoverShare = machines x changeover / ( runHours + machines x changeover )
Three machines on this order spend 10.5 hours setting up to save eight days of elapsed time. That is a good trade here and a bad one on a 500 kg order, and the share is the number that says which.
Symbols used above
Symbol
Stands for
Unit
changeover
Yarn change, cam setting, quality check and first-piece approval
h
slack
Time between planned completion and the due date
d
window
Due days multiplied by running hours per day
h
utilisation
Committed hours as a fraction of the window
%
How the result is derived
Step by step, from the values you type to the figure on screen.
The 6 inputs are read from the form on every keystroke: Order Quantity, Production Rate per Machine, Changeover per Machine, Days to the Due Date, Running Hours per Day and Machines Allocated.
Each value is checked against the accepted range in the input table below. A value outside its range stops the calculation rather than producing a misleading figure — the results blank out and a message appears.
The validated values are substituted into the expression above, which resolves Machines Needed to Meet the Date together with every supporting figure in one pass — no value is carried over from a previous entry.
The supporting outputs — Completion at the Allocated Count, Slack to the Due Date, Window Consumed, Total Running Hours, Hours Committed per Machine, Slack per Machine, Changeover Hours Paid, Changeover Share of Committed Time and Output at the Allocated Count — come from the same pass, so they always describe the same case as the headline figure.
Results are rounded for display only. The full-precision value is used throughout the chain, so reading a rounded intermediate figure back into the tool by hand can shift the last digit.
What each input means
Where to read each value on the floor, the unit it must be in, and the range the tool accepts.
Input
Unit
Accepted range
Default
What it means
Order Quantity
kg
10 to 500000 kg
9500
Production Rate per Machine
kg/h
0.5 to 200 kg/h
16.6
Changeover per Machine
h
0 to 48 h
3.5
Yarn change, cam and quality setting, first-piece approval
Days to the Due Date
d
0.5 to 200 d
9
Running Hours per Day
h/d
1 to 24 h/d
22
Machines Allocated
—
1 to 100
3
What the tool returns
The headline figure and every supporting value it is built from.
Output
Unit
What it tells you
Machines Needed to Meet the Date (headline result)
—
Smallest count that fits once each pays its changeover
194.2631 h committed per machine, finishing in 8.8301 days
3
0.1699 days of slack, 3.7369 h per machine
4
98.1127% of the window consumed; 10.5 h of it changeover
Four hours of slack on a nine day order is not a plan, it is a hope. One machine stopping for half a shift, one yarn lot arriving late, or one first-piece rejection and the date is gone - and there is no fourth machine in the calculation to recover it. The right reading of 98% window utilisation is that the order needs a fourth machine or an earlier start, not that it fits.
How to use it
Work through the input groups in order — The Order and The Window. The defaults are a realistic case, so you can change one value at a time and watch what moves.
There is no calculate button. Every figure recalculates as you type or drag, which is what makes this usable for a what-if sweep rather than a single answer.
Read Machines Needed to Meet the Date in the dark results panel — that is the headline figure, expressed in the unit shown.
Check the supporting rows underneath (Completion at the Allocated Count, Slack to the Due Date, Window Consumed, Total Running Hours, Hours Committed per Machine, Slack per Machine, Changeover Hours Paid, Changeover Share of Committed Time and Output at the Allocated Count) before acting on the headline — they are where an implausible input usually shows itself first.
Reset to defaults returns every field to the reference case, which is the quickest way to check whether a surprising result came from the tool or from an input you had changed earlier.
Where this is used
Process planning — establishing Machines Needed to Meet the Date before a trial is booked, so machine time and material in Knitting, Hosiery & Stretch-Fabric Control are committed against a calculated figure rather than an estimate.
Costing and quotation — Machines Needed to Meet the Date is an input to the cost sheet, and quoting from a worked number rather than a remembered one is what keeps a margin intact.
Troubleshooting — when the floor result drifts from plan, entering the measured values (starting with Order Quantity) shows how much of the gap in Machines Needed to Meet the Date each variable explains.
Teaching and study — the accepted ranges bracket normal Knitting, Hosiery & Stretch-Fabric Control practice, so moving one variable at a time shows the shape of the relationship rather than a single answer.
Reading the result
Typical bands and what each one is telling you.
Value
What it indicates
Utilisation under 85%
A plan with room to absorb a stoppage or a rework.
85 - 95%
Tight but workable if the yarn is on site and the quality is established.
Above 95%
No recovery capacity. Treat the date as at risk.
Changeover share above 15%
The order is being split too many ways for its size.
Assumptions and limits
The model assumes every allocated machine is identical, available for the whole window, and runs at the stated rate throughout; where machines differ in diameter, gauge or feeder count the rates differ and quantity should be allocated in proportion to rate rather than evenly. The production rate should already include machine efficiency - it is kilograms actually delivered per running hour, not the geometric maximum. Changeover covers yarn change, cam and quality setting and first-piece approval, and it is paid in full by every machine regardless of how small its share of the order is. Running hours per day should be measured rather than taken from the shift pattern. Nothing here models yarn availability, which is the constraint that most often decides whether a knitting order actually starts on the day the plan says it does, nor the queue for a shared changeover crew.
Every input is bounded to the range normal practice occupies (Order Quantity 10 to 500000 kg, Production Rate per Machine 0.5 to 200 kg/h and Changeover per Machine 0 to 48 h, and so on for the rest). Those bounds are guard rails against typing errors, not a claim that the formula fails one unit outside them.
The calculation is deterministic: the same inputs always give the same result. It carries no allowance for machine condition, operator skill, ambient conditions or lot-to-lot material variation unless an input above explicitly represents one.
Nothing is sent anywhere. The maths runs in your browser, so the numbers you type never leave the page.
Standards and further reading
ISO 22400-2 - key performance indicators for manufacturing operations management.
ISO 9001 - quality management systems, for the first-piece approval inside the changeover.
ISO 4921 - knitting, basic concepts, vocabulary.
ASTM D3887 - tolerances for knitted fabrics, which the first-piece check is against.
Questions people ask
Why does the machine count use the window minus one changeover rather than minus all of them?
Because the machines set up in parallel, not in sequence. Each machine loses its own 3.5 hours from its own window, and all of those hours are lost simultaneously at the start of the job, so from any single machine's point of view the runnable window is the full window less one changeover. The total changeover hours consumed across the shed is the count multiplied by the changeover, and that figure matters for capacity accounting - it is reported separately here for exactly that reason - but it is not what constrains the date. Confusing the two produces a machine count that is too high, which then costs more changeover, which is a satisfying kind of wrong.
Is splitting an order across machines always worth it?
No, and the changeover share is the test. Splitting buys elapsed time and pays for it in setup hours and in variability: every machine is a separate set of cam settings, a separate first piece, and a separate opportunity for the fabric to come out slightly different, which shows up as shade or weight banding between rolls that a customer will attribute to dyeing. On a large order the setup cost is trivial - 10.5 hours against 572 is under two per cent - and the variability is manageable with disciplined first-piece control. On a 600 kg order across three machines the setup would be 22% of the committed time and the between-machine variation would be spread across a lot the customer sees as one, which is rarely a good trade.
What should the running hours per day actually be?
Whatever the machine genuinely runs, which is not the shift length. Twenty-two hours of a twenty-four hour day allows two hours for doffing, cleaning, oiling, lint removal and the short stops that are part of normal operation, and that is about right for a well-run knitting hall on continuous shifts. Using twenty-four produces a plan that fails quietly; using sixteen when the hall runs three shifts wastes capacity that exists. The figure should come from measured machine running hours over a recent period rather than from the shift pattern, and it should be reviewed when the pattern changes, because it is the quantity that silently absorbs every planning assumption nobody wrote down.
The production rate is per machine - what if the machines differ?
Then this calculation gives a first cut and the allocation needs doing properly. Machines of different diameter, gauge or feeder count produce at genuinely different rates for the same quality, and allocating an order evenly across unequal machines means the slowest one sets the completion date while the fastest sits idle. The practical approach is to run this with the slowest machine's rate to get a conservative machine count and a date that will hold, then allocate quantity in proportion to each machine's actual rate so they finish together. Where the machines differ enough that the fabric differs - a different diameter changes the width, a different gauge changes everything - they should not be sharing one order at all.
