Stitch Density Measurement for Bags: Count Wales and Courses per Centimetre, Set Loop Length, and Catch Gauge Drift Before Bulk
How is stitch density measured on a knitted bag? Count the wales and the courses per centimetre through a counting glass with a 25 mm aperture, take ten readings across the panel, and record loop length in millimetres on a separate unroved specimen. Three numbers, taken under the ISO 139 atmosphere, and a spread of more than 5 percent between readings is the earliest signal that a machine is drifting. Density is the least expensive measurement in knit QC and the one most often skipped.
Why Stitch Density Is the First Number Buyers Skip
Stitch density is the lowest-cost measurement available in knit quality control and it is the one most often skipped, because it is not a defect. An inspector counting attributes at goods-in is looking for holes and dropped stitches, and a panel with the wrong density has neither. It looks fine on the table and then behaves differently in the field, in the wash, or on the shelf.
That is the whole argument for measuring it: density is the structural variable behind most of the performance outcomes a buyer actually cares about. Abrasion life, dimensional stability, handle elongation and even apparent shade all move with loop length, and loop length is set on the machine rather than at the inspection table. Measuring density is how a buyer finds out what the machine was doing.
The practical reason it gets skipped is that nobody has written the number into the specification. A tech pack that specifies gauge E12 and a yarn count of 300D but no wales or courses per centimetre has left the structural variable uncontrolled, and two production runs can both be compliant while being measurably different bags. One line in the tech pack fixes this permanently.
Wales, Courses and Loop Length: The Three Numbers
Three numbers describe a knitted structure and only the third is usually measured. Wales per centimetre is the count of vertical columns of loops; courses per centimetre is the count of horizontal rows. Together they give the stitch density, and on a typical seamless bag body run at gauge E12 with a 300D polyester yarn those figures land around 3.8 wales and 4.5 courses per centimetre.
Loop length is the one that matters most and the one rarely recorded. It is the length of yarn in a single loop, measured in millimetres, and on a bag body of this kind it sits near 4.2 mm. Loop length controls everything downstream: longer loops give a softer, more open fabric with lower abrasion resistance and more shrinkage; shorter loops give a tighter, heavier panel that uses more yarn per bag.
The three are related but not interchangeable. Two machines at the same gauge E12 can produce the same wale count with different loop lengths if the take-down differs, and the bags will weigh differently and wear differently while measuring identically on the two counts most people take. This is exactly why the loop length belongs on the spec sheet.
The Counting Method, Step by Step
The method takes about fifteen minutes per panel and needs a counting glass, a millimetre rule, a needle and a conditioned room. Nothing in it requires a laboratory, which is the point: it is a floor measurement that a buyer's own representative can repeat without booking a testing slot.
- Condition the panel for at least 4 hours under the ISO 139 atmosphere of 20 degrees Celsius and 65 percent relative humidity before any measurement.
- Lay the panel flat on a bench without tension, because a knitted structure held under tension distorts by several percent and every reading taken that way is wrong.
- Choose five positions: centre, and one roughly 50 mm in from each edge. Edge readings differ from centre readings by nature and should be recorded separately.
- Place a counting glass with a 25 mm square aperture on the first position and count the wales across the aperture, then turn the glass 90 degrees and count the courses.
- Divide by 2.5 to convert a 25 mm count into a per-centimetre figure, and record both numbers to one decimal place rather than rounding to whole stitches.
- Repeat at all five positions, giving ten readings per panel, and take the spread as well as the mean. The spread is the number that catches machine drift.
- For loop length, unpick a single course with a needle, straighten ten loops gently without stretching them, measure the total and divide by twenty.
- Compare the mean against the specification and the spread against the tolerance. A mean inside tolerance with a spread over 5 percent is a drifting machine, not a passing panel.
Two of those eight steps carry most of the accuracy. Conditioning matters because a knitted panel picks up and loses moisture and the loop geometry moves with it, so an unconditioned reading taken in a humid room in Xiamen in July will not match the same panel read in a dry warehouse in Rotterdam in January. Laying flat without tension matters for the same reason in mechanical form.
Gauge, Yarn Count and Density: Which One Drifted
When a density reading is out, three variables could have moved and the fix is different for each. Gauge is the needle spacing on the machine and is essentially fixed for a given run, so it rarely drifts. Yarn count can vary between lots. Take-down tension moves constantly and is the usual culprit. Telling them apart is a two-minute exercise.
| Symptom | Likely cause | How to confirm | Usual fix |
|---|---|---|---|
| Courses per cm fall, wales unchanged | Take-down tension too high | Check the take-down setting against the run sheet | Reset take-down and re-measure after 50 pieces |
| Wales per cm fall, courses unchanged | Wrong needle set-up or a gauge change | Compare needle bed set-up to the approved sample record | Re-set the needle set-up; gauge changes need re-sampling |
| Both fall, weight per bag falls | Loop length increased, yarn feed slack | Measure loop length on ten unroved loops | Adjust the yarn feed and re-weigh five bags |
| Both rise, panel feels stiff | Loop length reduced, yarn feed tight | Measure loop length; check yarn tension at the feeder | Ease the yarn feed; check for yarn drag at the guide |
| Density correct, weight per bag varies | Yarn count variation between lots | Weigh a known length of yarn and compare to the count | Quarantine the yarn lot and re-run with the approved lot |
| Density varies across the panel only | Feeder-to-feeder tension spread | Take readings at five positions and compare the spread | Re-tension the feeders; a spread over 5 percent shows as a shade band |
The last row is the one with the most commercial consequence. A feeder-to-feeder tension spread does not usually produce a stitch defect, so it passes an attribute inspection cleanly. What it produces is a visible banding across the panel that reads as a shade fault, and the buyer then argues about dye lots when the actual cause is a tension setting.
Tolerance: What Spread Is Acceptable
Two tolerances are needed and buyers usually write one. The mean must sit inside a band against the specification, and the spread between readings inside a second, tighter band. A panel can pass the first and fail the second, and that combination is precisely the signature of a machine that is drifting but has not yet drifted far.
- Wales per centimetre, mean
- 3.8 plus or minus 0.2 at gauge E12 with 300D polyester
- Courses per centimetre, mean
- 4.5 plus or minus 0.25 under the same set-up
- Loop length
- 4.2 mm plus or minus 0.2 mm, measured on ten unroved loops
- Spread across five positions
- Not more than 5 percent between the highest and lowest reading
- Weight per bag, correlated check
- Plus or minus 5 percent against the approved reference bag
- Conditioning before measurement
- 4 hours minimum at 20 degrees Celsius and 65 percent relative humidity per ISO 139
- Readings per panel
- Ten: five positions, two counts each, edge readings recorded separately
- Re-check trigger
- Re-measure every 500 pieces, and after any yarn lot change or needle change
Weight per bag is in that list on purpose. It is the fastest cross-check on density that exists, because it needs a scale and nothing else, and a bag that measures correct on wales and courses but weighs 6 percent light is telling the buyer that the loop length moved while the counts happened to stay put.
What Density Predicts About the Finished Bag
Density is worth measuring because it predicts four outcomes that buyers otherwise discover after the goods have shipped. None of these is an attribute, none is visible at goods-in, and all four are expensive once the container has left.
Abrasion life
A tighter structure with shorter loops resists surface abrasion better. Where a programme specifies a Martindale end point in cycles, loop length is the variable that decides whether it is met.
Dimensional stability
Longer loops mean more relaxation left in the panel. A bag knitted slack will shrink and relax more in the first wash and the first month on a fixture.
Handle elongation
Density at the handle joinery governs how the load spreads. A loose structure concentrates strain at the join and shows up as elongation under repeated 5 kg cycles.
Apparent shade
A density spread reflects light differently across one panel, producing bands that look like a dye fault and are not. Measure before arguing about dye lots.
Yarn consumption
Loop length drives grams per bag directly. A 0.2 mm shift across a run of 20,000 pieces is a material difference in yarn drawn, which is why the number is watched on the floor.
Hand and drape
Buyers reject bags for feel more often than for any measurable defect, and feel is mostly loop length. Specifying the number is the only way to make a hand feel repeatable.
Where Density Measurement Goes Wrong
Four errors account for most bad readings, and all four produce a number that looks plausible. Measuring on a tensioned panel, measuring before conditioning, counting under a lens with a distorted edge, and rounding to whole stitches are the usual suspects, and each one moves the result by enough to turn a pass into a fail or the reverse.
Reading on a curved or assembled bag is the fifth error and the most common in practice. Stitch density is measured on a flat, relaxed panel, not on a bag that has been stuffed or assembled, because assembling puts the panel under tension and tension changes every count. Where a buyer wants to check a finished bag, cut a specimen and measure the specimen.
The sixth is comparing across gauges. A reading of 3.8 wales per centimetre means one thing at gauge E12 and something quite different at gauge E7, where a coarser structure with a heavier yarn might sit near 2.4 wales and 3.0 courses. Every density figure on a spec sheet needs the gauge and the yarn count written beside it or it is not a specification.
Building Density into the QC Plan
Density belongs in the QC plan at three points: at sample approval, where the numbers are set; at the start of bulk, where the first 50 pieces are measured before the run is released; and at a fixed interval through the run, typically every 500 pieces or after any yarn lot or needle change. Three checkpoints is enough for most programmes.
It also belongs on the inspection report as a recorded measurement rather than an attribute. Ten readings, mean and spread, alongside the dimensional results, under the same conditioning clause. That single addition converts a report that documents appearance into one that documents structure, and it gives a buyer something to compare against when a later lot behaves differently.
The density line for a tech pack
- Gauge E12, 300D polyester, 3.8 wales and 4.5 courses per centimetre plus or minus 0.2 and 0.25, loop length 4.2 mm plus or minus 0.2 mm, spread across five positions not above 5 percent, conditioned 4 hours at 20 degrees Celsius and 65 percent relative humidity per ISO 139, re-measured every 500 pieces.
Set stitch density targets on a knit bag programme
Send the bag type, gauge preference and yarn count. We will return the wales, courses and loop length targets with the tolerance band, recorded on the inspection report alongside AQL 2.5, and quote FOB Xiamen at 100 pcs per style and colourway with 7 working days sampling and 30 days bulk. Start on the contact page.
Frequently Asked Questions
What is stitch density on a knitted bag?
The number of wales, which are vertical columns of loops, and courses, which are horizontal rows, per unit length. It is normally quoted per centimetre and taken through a counting glass, and it is the structural measurement behind abrasion life, shrinkage and hand.
How do you measure stitch density?
Condition the panel for 4 hours, lay it flat without tension, place a 25 mm counting glass at five positions, count wales then courses at each, divide by 2.5 to get a per-centimetre figure, and take the spread across the ten readings as well as the mean.
What is loop length and why does it matter?
Loop length is the length of yarn in one loop, measured in millimetres, around 4.2 mm on a typical bag body. It controls softness, abrasion resistance, shrinkage and yarn consumption, and two runs at the same gauge can differ in loop length while showing identical wale and course counts.
What tolerance should be set on stitch density?
Two: around plus or minus 0.2 wales per centimetre on the mean, and no more than 5 percent spread between the highest and lowest of the five positional readings. A mean inside tolerance with a spread above 5 percent indicates a drifting machine rather than a passing panel.
Why must the panel be conditioned before measuring?
A knitted structure takes up and loses moisture, and loop geometry moves with it. Without conditioning at 20 degrees Celsius and 65 percent relative humidity under ISO 139, a reading taken in a humid room will not match the same panel read somewhere dry.
Can stitch density be measured on a finished assembled bag?
Not reliably. Assembling puts the panel under tension and tension distorts every count. Cut a specimen from the bag and measure the specimen flat, or measure the flat panel before assembly, which is what the specification figure refers to.
What causes stitch density to drift during a run?
Take-down tension is the most common cause, moving course count without touching wales. Yarn feed tension changes loop length and therefore weight per bag. Yarn count variation between lots shows up as a weight change with the counts apparently correct.
How does stitch density affect abrasion resistance?
A tighter structure with shorter loops resists surface abrasion better. Where a programme sets a Martindale end point in cycles under ISO 12947-2, loop length is the variable that decides whether the end point is reached, so it is fixed before the test rather than discovered by it.
Can a density problem look like a shade problem?
Yes, and it frequently does. A feeder-to-feeder tension spread produces visible banding across a panel that reads as a dye fault, passes a visual attribute inspection, and is resolved by re-tensioning the feeders rather than by changing the yarn lot.
How often should density be re-measured in bulk?
At the start of the run on the first 50 pieces before release, then about every 500 pieces, and immediately after any yarn lot change or needle change. Three checkpoints is enough for most programmes and costs about fifteen minutes each.
Does gauge change the density figures?
Yes. Around 3.8 wales per centimetre is a gauge E12 figure with 300D polyester; a coarser gauge E7 structure with a heavier yarn might sit near 2.4 wales and 3.0 courses. Every density figure needs the gauge and yarn count written beside it to mean anything.
Should stitch density appear on the inspection report?
Yes, as a recorded measurement rather than an attribute. Ten readings with mean and spread, alongside the dimensional results and under the same conditioning clause, converts a report about appearance into one that documents structure.
What is the fastest cross-check on density?
Weight per bag. It needs a scale and nothing else, and a bag that measures correct on wales and courses but weighs 6 percent light is telling the buyer that loop length moved while the counts happened to stay where they were.
Where does density sit in a QC plan?
At three points: sample approval where the numbers are set, bulk start where the first 50 pieces are measured before the run is released, and a fixed interval through the run. Setting the numbers at sampling, at 7 working days, is the point where change is still free.
People Also Ask
How do you measure stitch density?
Count wales and courses through a 25 mm counting glass at five positions on a flat, conditioned panel, divide by 2.5 for a per-centimetre figure, and record the spread across the ten readings.
What is a normal stitch density for a knitted bag?
Around 3.8 wales and 4.5 courses per centimetre at gauge E12 with 300D polyester. A coarser gauge E7 structure with heavier yarn sits nearer 2.4 wales and 3.0 courses.
What is loop length in knitting?
The length of yarn in a single loop, about 4.2 mm on a typical bag body. It controls hand, abrasion life, shrinkage and yarn consumption, and it is set on the machine rather than at inspection.
Why does my knitted panel show banding?
Usually a feeder-to-feeder tension spread rather than a dye fault. Take five positional readings; a spread above 5 percent confirms it and the fix is re-tensioning the feeders.
What tolerance should I set for stitch density?
Plus or minus 0.2 on the mean wale count, plus or minus 0.2 mm on loop length, and no more than 5 percent spread between positional readings on a single panel.
Sources and further reading
Every figure on this page is either our own programme data or attributed below. Open the originals before you write them into a specification.
- ISO 139 Textiles, standard atmospheres for conditioning and testingISO The 20 degrees Celsius and 65 percent relative humidity conditioning atmosphere required before any stitch density reading.
- ISO 12947-2 Textiles, abrasion resistance by the Martindale methodISO The abrasion end point that loop length largely determines, measured in cycles on separate specimens.
- ISO 3801 Textiles, determination of mass per unit length and mass per unit areaISO The basis for the weight per bag cross-check used as the fastest confirmation that loop length has moved.
- WHOLEGARMENT knitting machinesShima Seiki The machine class on which seamless knitted bag panels are produced, where gauge and take-down set the structure.