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Loop length is not a setting you choose. It is a window the yarn count opens.
Tightness Factor K
—
Square root of tex divided by loop length in mm
Setting Window, Weight & Consumption
Position in the Window
—%
Tight Limit Loop Length
—mm
Slack Limit Loop Length
—mm
Workable Window
—mm
Fabric Weight
—g/m2
Needles in the Cylinder
—
Yarn per Course
—m
Courses Knitted
—/min
Yarn Consumption
—kg/h
The tight and slack limits are properties of the fibre, the yarn quality and the machine gauge rather than universal constants; the defaults reflect cotton single jersey on a medium gauge and should be re-established for other fibres. Fabric weight is calculated at the stitch density entered, which for a greige fabric on the machine is not the density it will have after relaxation, wet processing or compacting - expect the finished figure to be substantially higher, driven almost entirely by stitch density rather than by loop length. Needle count is the geometric figure from gauge and diameter and ignores any needles removed for a pattern. Yarn consumption assumes every feeder knits every revolution and makes no allowance for machine efficiency, waste at start-up or the extra yarn taken by elastane or plating feeders. This is a single jersey model: rib, interlock and purl consume differently per course and their tightness factors are conventionally quoted on a different basis.
Using this calculator
About the Stitch Cam Setting Window, Tightness Factor & Fabric Weight
The formula
This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.
The tightness factorK = sqrt( tex ) / loopLength
Loop length alone says nothing: 2.9 mm is tight for a fine yarn and slack for a coarse one. Dividing the square root of the count by the loop length gives a quantity that is constant for fabrics of the same handle, which is why it and not the loop length is the transferable setting.
High K is a short loop, so the tight limit produces the smaller number. Reading the window the wrong way round is the most common error with tightness factors and it produces a setting at the opposite end of the range.
Fabric weight from stitch geometrygsm = coursesPerCm x walesPerCm x loopLength x tex / 100
Loops per square metre multiplied by the yarn in each loop. Everything cancels to this compact form because tex is grams per thousand metres and loop length is in millimetres - a coincidence of units that makes the constant exactly 100.
Machine outputneedles = gauge x pi x cylinderDia consumption = coursesPerMin x needles x loopLength x tex
Needle count is gauge times circumference in inches, so a 30 inch 24 gauge cylinder carries 2,262 needles. Consumption follows directly and is the figure that decides how many cones the machine eats per shift.
Symbols used above
Symbol
Stands for
Unit
K
Tightness factor, sqrt(tex) over loop length in mm
—
loop length
Yarn consumed by one knitted loop
mm
gauge
Needles per inch of cylinder circumference
npi
course
One horizontal row of loops, one per feeder per revolution
—
How the result is derived
Step by step, from the values you type to the figure on screen.
The 10 inputs are read from the form on every keystroke: Yarn Count, Loop Length, Tight Limit, Slack Limit, Machine Gauge, Cylinder Diameter, Feeders, Machine Speed, Courses and Wales.
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 Tightness Factor K together with every supporting figure in one pass — no value is carried over from a previous entry.
The supporting outputs — Position in the Window, Tight Limit Loop Length, Slack Limit Loop Length, Workable Window, Fabric Weight, Needles in the Cylinder, Yarn per Course, Courses Knitted and Yarn Consumption — 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
Yarn Count
tex
2 to 200 tex
20
Loop Length
mm
0.5 to 20 mm
2.9
Tight Limit
K
0.8 to 3 K
1.65
Highest tightness factor the yarn will knit at
Slack Limit
K
0.5 to 3 K
1.3
Lowest before the loop distorts
Machine Gauge
npi
3 to 44 npi
24
Cylinder Diameter
in
3 to 60 in
30
Feeders
—
1 to 250
96
Machine Speed
rpm
1 to 60 rpm
25
Courses
/cm
2 to 80 /cm
17
Wales
/cm
2 to 80 /cm
13
What the tool returns
The headline figure and every supporting value it is built from.
Window runs 2.7104 mm to 3.4401 mm, so 0.7297 mm wide
2
Current setting sits 25.9846% into the window from the tight end
3
2,261.9467 needles, 6.5596 m of yarn per course
4
128.18 g/m2 at 2,400 courses/min and 18.8918 kg/h
At 26% into the window the fabric is set toward the tight end, which is where single jersey for printing and for dimensional stability belongs. The same yarn at the slack limit would knit at 3.44 mm and about 152 g/m2 - a 19% heavier fabric from the same cone, with a softer handle and considerably worse shrinkage. That is the trade the cam is making, and it is worth knowing which end of the window a setting sits at before anyone calls it right or wrong.
How to use it
Work through the input groups in order — Yarn & Loop and Machine & Fabric. 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 Tightness Factor K in the dark results panel — that is the headline figure, expressed in the unit shown.
Check the supporting rows underneath (Position in the Window, Tight Limit Loop Length, Slack Limit Loop Length, Workable Window, Fabric Weight, Needles in the Cylinder, Yarn per Course, Courses Knitted and Yarn Consumption) 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 Tightness Factor K 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 — Tightness Factor K 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 Yarn Count) shows how much of the gap in Tightness Factor K 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
K 1.40 - 1.50
The classic reference band for cotton single jersey.
K above 1.60
Firm and dimensionally stable, but yarn tension and needle load rise sharply.
K below 1.30
Slack. Loop distortion, spirality and poor recovery become likely.
Position 20 - 60% in window
A setting with room to move in both directions.
Assumptions and limits
The tight and slack limits are properties of the fibre, the yarn quality and the machine gauge rather than universal constants; the defaults reflect cotton single jersey on a medium gauge and should be re-established for other fibres. Fabric weight is calculated at the stitch density entered, which for a greige fabric on the machine is not the density it will have after relaxation, wet processing or compacting - expect the finished figure to be substantially higher, driven almost entirely by stitch density rather than by loop length. Needle count is the geometric figure from gauge and diameter and ignores any needles removed for a pattern. Yarn consumption assumes every feeder knits every revolution and makes no allowance for machine efficiency, waste at start-up or the extra yarn taken by elastane or plating feeders. This is a single jersey model: rib, interlock and purl consume differently per course and their tightness factors are conventionally quoted on a different basis.
Every input is bounded to the range normal practice occupies (Yarn Count 2 to 200 tex, Loop Length 0.5 to 20 mm and Tight Limit 0.8 to 3 K, 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 4921 - knitting, basic concepts, vocabulary.
ISO 3801 - textiles, woven fabrics, determination of mass per unit length and mass per unit area.
ASTM D3887 - tolerances for knitted fabrics.
ISO 1144 - universal system for designating linear density, the tex system.
Questions people ask
Why does the tightness factor use the square root of the count?
Because yarn diameter goes as the square root of linear density, and what governs how tightly loops can pack is the diameter, not the mass. Doubling the tex of a yarn increases its diameter by about 41%, not by 100%, so a loop length scaled directly with count would be badly wrong across the range. Dividing the square root of tex by loop length produces a dimensionless-in-practice quantity that stays roughly constant for fabrics that look and behave the same, which is exactly what a transferable setting needs to be. It is the same reasoning behind the cover factor in weaving, and it is why K values quoted for cotton single jersey hold across a wide span of counts.
How is loop length actually measured on the machine?
By unravelling. A known number of wales - usually 100 - is unpicked from a single course, the yarn is straightened under a specified small tension, and its length is measured and divided by the loop count. Doing it under too much tension is the classic error, because knitting yarn is extensible and a few per cent of stretch becomes a few per cent of loop length and directly a few per cent of fabric weight. The alternative route, back-calculating from fabric weight and stitch density, is quicker but circular for this purpose: it assumes the relationship the calculation is meant to check. Where a positive feeder is fitted, the delivered length per revolution gives a third and independent estimate, and disagreement between the three is diagnostic.
Do the tight and slack limits depend on the fibre?
Substantially. The defaults here reflect cotton and cotton-rich single jersey, where the yarn is inextensible enough that a short loop loads the needles hard and hairy enough that a slack loop distorts. Filament polyester knits acceptably at higher K because the yarn is smoother and slides through the needle more freely; wool and acrylic tolerate slacker settings without visible distortion because of their bulk and recovery. The window also narrows with machine gauge, since a fine gauge leaves less clearance for the yarn regardless of the count. The right practice is to establish the pair of limits for each fibre and gauge combination on your own machines and keep them, rather than transferring a published number.
Why does the calculated weight differ from the fabric on the roll?
Because the calculation is of greige fabric at the stitch density entered, and stitch density moves. Relaxation alone shifts courses and wales per centimetre by several per cent as the fabric comes off tension; wet relaxation moves them further, and finishing - compacting in particular - is deliberately designed to move them a long way. A single jersey that calculates at 128 g/m2 on the machine will commonly finish between 150 and 170 g/m2 after relaxation and compacting, and the difference is almost entirely stitch density rather than any change in loop length, which is fixed at knitting. Use the calculated figure to control the machine and the measured finished figure to control the customer specification.
