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Stitch length is the master variable in knitting. Everything else follows from it.
Stitch Length
—mm
Yarn consumed by a single loop
Derived Quality
Tightness Factor (K)
—
Yarn Linear Density
—tex
Course Length
—m
Yarn Mass per Course
—g
Single jersey normally sits at K = 1.4-1.5. Below 1.3 the fabric is slack and unstable; above 1.6 it knits hard and drops in productivity.
Using this calculator
About the Stitch Length & Course Length Estimator
The formula
This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.
Stitch length (loop length) from an unravelled coursestitchLength = courseLength / needles
courseLength is the yarn in one complete course, entered in mm, so stitchLength falls out in mm with no conversion. needles must be the needles that actually formed that course: on a needle-out arrangement, or where the sample does not span the full revolution, count the loops in the unravelled length rather than reading the cylinder needle count off the machine plate.
English cotton count converted to linear densitytex = 590.5 / yarnNe
590.5 is 453.59237 g per pound divided by 768.096 m per 840-yard hank, times 1000 - the grams in 1000 m of a 1 Ne yarn. Ne is an indirect system so it divides: 30 Ne is a finer, lighter yarn than 20 Ne, and the tightness factor needs a direct density to work with.
The square root is there because tex is proportional to yarn cross-sectional area while loop area goes as stitchLength squared, so sqrt(tex) / stitchLength compares yarn diameter against loop size. K carries units of tex^0.5 per mm and is only comparable against figures quoted on that same basis - a K derived from cotton count, or with the loop in cm, sits on a different scale entirely.
Yarn drawn by one course, in gramsmassPerCourse = (courseLength / 1000) x tex / 1000
The first division converts mm to metres and is reported separately as courseLengthM; the second converts tex, which is grams per 1000 m, into grams per metre. Multiply massPerCourse by the number of feeders and by machine rpm to get yarn draw per minute for creel and positive-feed planning.
Symbols used above
Symbol
Stands for
Unit
courseLength
Course Length
mm
needles
Needles in Course
no.
yarnNe
Yarn Count
Ne
stitchLength
Stitch Length
mm
tightnessFactor
Tightness Factor (K)
—
tex
Yarn Linear Density
tex
courseLengthM
Course Length
m
massPerCourse
Yarn Mass per Course
g
How the result is derived
Step by step, from the values you type to the figure on screen.
Take the sample away from start-up and from any stop mark, then cut and unravel one complete course. A part course scaled up to full needle count carries its own scaling error into every figure below it.
Measure the unravelled yarn with the crimp pulled out but the yarn not extended - a course length tester, or a crimp tester at the sort of pretension used for count testing (of the order of 0.5 cN/tex). Measuring by hand under thumb tension reads long and makes the fabric look slacker than it is.
Divide by the needle count in that course. What comes out is the yarn in a single loop, and that is the machine-independent number: at the same gauge and the same count, a 2.9 mm loop knitted on a 20 inch cylinder and on a 34 inch cylinder gives the same fabric, only in different widths.
Convert the yarn count to tex. Ne cannot be substituted into K as it stands, because K needs a density that rises with yarn thickness rather than one that falls with it.
Form K = sqrt(tex) / stitchLength. K states how much yarn has been forced into a given loop area, which is why it is the figure to compare across counts, gauges and machines - the raw stitch length is not comparable across yarn counts.
Read the mass per course against the machine. Multiplied by feeders and revolutions it is the yarn draw rate, and it is the check on whether the creel and positive feed can actually sustain the setting you have just dialled in.
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
Course Length
mm
1 to 500000 mm
6960
Needles in Course
no.
1 to 10000 no.
2400
Yarn Count
Ne
1 to 200 Ne
30
What the tool returns
The headline figure and every supporting value it is built from.
A 2,400 needle cylinder running 30 Ne cotton at 2.90 mm loop gives K = 1.53, which sits above the 1.40 to 1.50 window normal for single jersey - this machine is knitting tight. Opening the course length to 7,244 mm lifts the loop to 3.02 mm and brings K to 1.47. That is the sensitivity worth remembering: K goes as 1 / stitchLength, so 4% more yarn per course buys about 4% less K, and roughly 4% less fabric weight per square metre.
How to use it
Work through the input groups in order — Course Measurement and Yarn. 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 Stitch Length in the dark results panel — that is the headline figure, expressed in mm.
Check the supporting rows underneath (Tightness Factor (K), Yarn Linear Density, Course Length and Yarn Mass per Course) 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
Machine setting and shift QC - the stitch cam setting is verified by unravelling a course, and the positive feed wheel is sized to deliver the target course length rather than trusting the cam graduations.
GSM control - from Munden's relationship, stitch density goes as 1 / stitchLength squared, so fabric weight goes as tex / stitchLength. At a fixed count, 1% more course length is about 1% less GSM, which is how weight is trimmed onto a buyer's target without touching the yarn.
Lot uniformity across machines - several machines knitting one order must be set to the same course length, not the same cam number. A course-length spread between machines appears as weight bands in greige and, after dyeing, as shade bands within the lot.
Shrinkage and spirality control - residual shrinkage is largely the distance the fabric still has to travel to its relaxed state, so a low K means more of that distance is left in the fabric when it ships. Spirality has a different root cause, the residual torque of a single yarn, but a tighter loop restrains that torque, which is why slack jersey in a lively count spirals worst.
Yarn costing and machine loading - mass per course times feeders times rpm gives kilograms per hour, which sets both the creel replenishment interval and the yarn cost per kilogram of greige fabric.
Reading the result
Typical bands and what each one is telling you.
Value
What it indicates
K below 1.30
Very slack. Open, low-cover fabric with poor dimensional stability, high residual shrinkage and a marked tendency to curl and spiral. Occasionally deliberate for very light airy jersey, but it will not hold shape through laundering.
K 1.30 to 1.40
Slack single jersey. Soft, light and economical on yarn per square metre, but relaxation shrinkage runs high and the fabric gives up width and length in finishing and again in wash.
K 1.40 to 1.50
The normal working window for cotton single jersey. Best compromise between handle, dimensional stability, machine speed and stop rate. Most T-shirt jersey specifications sit inside this band.
K 1.50 to 1.60
Tight. Firmer handle, better bursting strength and pilling resistance, and more weight for the same count - but yarn tension in the knitting zone rises, needle and sinker wear increase, and holes become the characteristic defect. The worked example sits here.
K above 1.60
Hard knitted. Expect frequent needle breakage, high stop rates and a boardy handle. Justified for coating base cloth or dense pique, not for general jersey.
Reading the bands at all
These figures are cotton single jersey figures, quoted in tex^0.5 per mm. Rib, interlock and fleece run to their own ranges, and man-made and blended yarns of the same tex behave differently in the loop, so judge those structures against a mill's own record rather than against the jersey window.
Assumptions and limits
Single jersey normally sits at K = 1.4-1.5. Below 1.3 the fabric is slack and unstable; above 1.6 it knits hard and drops in productivity.
Every input is bounded to the range normal practice occupies (Course Length 1 to 500000 mm, Needles in Course 1 to 10000 no. and Yarn Count 1 to 200 Ne, 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 2060 / ASTM D1907 - yarn linear density by the skein method, tested at a pretension of the order of 0.5 cN/tex. This is where a disputed count is settled, and it produces the tex that goes into K.
ISO 4921 - knitting, basic concepts and vocabulary. It defines course, wale and loop (stitch) length, so a specification written against it means the same thing in the supplier's mill and the buyer's lab.
ASTM D3776 - mass per unit area of fabric. The GSM that a stitch length setting is supposed to deliver is verified against this test, in practice by cutting a known area with a circular cutter and weighing it after conditioning. ISO 3801 determines the same quantity but its scope is written for woven fabric, so quoting it on a knit is mill convention rather than the stated scope of the method.
ISO 6330 with ISO 5077, or AATCC 135 - washing procedure and dimensional change after domestic laundering. A slack K shows up as shrinkage here long before anyone notices it on the knitting floor.
Loop length measurement itself is not covered by a method I would cite by designation. Mill practice is a course length tester, or a crimp tester set to the count-testing pretension, on a full unravelled course.
Questions people ask
What is the difference between course length, stitch length and loop length?
Stitch length and loop length are the same quantity - the yarn consumed by one knitted loop. Course length is the yarn in one complete course across every needle in the revolution, so it is stitch length multiplied by the needle count. Mills set and monitor machines on course length because that is what a positive feed delivers and what can physically be unravelled and measured, while specifications quote stitch length because it is independent of cylinder diameter and needle count.
How do I measure course length without inflating it?
Unravel a complete course from a marked point, then measure it with the crimp removed but the yarn not extended - a course length tester, or a crimp tester at the sort of pretension used for count testing, around 0.5 cN/tex. Measuring by hand under thumb tension routinely adds a few percent, and since K and GSM both move roughly one for one with stitch length, that error passes straight into the fabric specification. Take courses from several feeders and average, because feeder-to-feeder variation on a multi-feed machine is real and is often the thing you are actually chasing.
K comes out at 1.53 against a 1.45 target. What should I change?
Change the course length, not the count. K goes as the square root of tex, so it takes roughly a 10% count change to shift K by 5%, whereas a 5% change in course length does the same job directly and leaves yarn cost, strength and dye behaviour alone. Open the stitch cams a step and re-check by unravelling: in the worked example, going from 6,960 mm to 7,244 mm per course moves K from 1.53 to 1.47.
Does machine gauge affect K, and do these bands apply to rib and interlock?
Gauge does not enter K itself - it is a comparison of yarn thickness against loop size, so the same K means the same relative tightness on an E18 and an E28 machine. Gauge does limit which stitch lengths are reachable, since needle spacing sets both the shortest loop that will clear and the count band the machine can run at all. The bands quoted above are for single jersey; rib and interlock have their own working ranges and should be judged against a mill's own record for that structure rather than against jersey figures.
The tool calls K dimensionless. Is it?
Not as computed here. sqrt(tex) / stitchLength with the loop in mm carries units of tex^0.5 per mm, which is the basis every published single jersey figure of 1.4 to 1.5 is quoted on, so the numbers are comparable as long as everyone stays on that basis. It is called dimensionless in the loose sense that it does not change with machine size or fabric area. If a K arrives quoted on cotton count, or with the loop in cm or inches, it is on a different scale and cannot be compared with these bands without recalculating from tex and mm.
