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Unit 1 of 4 · B.Sc Textile Sem 4

Unit 1: Yarn count & fabric weight

Fabric Quality Analysis notes · PTU syllabus (BSTD 401-20)

3 min read5 topics9 exam questions
On this page
  1. Unit summary
  2. Yarn numbering systems
  3. Effect of yarn count on cost and performance
  4. EPI and PPI with a pick glass
  5. Crimp
  6. Fabric weight (GSM)
  7. Key terms
  8. Quick revision
  9. Important questions

Unit summary

Fabric specifications are written in numbers — count, ends and picks, crimp and GSM. This unit covers direct and indirect yarn numbering, the effect of count on cost and performance, conversions, finding EPI and PPI with a pick glass, crimp calculation and fabric weight (GSM).

After this unit you can

  • Use direct and indirect yarn count systems and convert between them
  • Relate yarn count to cost and performance
  • Measure EPI and PPI with a pick glass
  • Calculate crimp and GSM

PTU syllabus topics

  • Yarn numbering systems (direct and indirect)
  • yarn count's effect on cost and performance
  • conversion calculations
  • using a pick glass to find EPI and PPI
  • crimp calculation
  • GSM calculation and global methods of expressing fabric weight
Key formulasFabric construction calculations

  • GSM

    Weight of sample (g) / area (m²)

  • Crimp %

    (Yarn length − fabric length) / fabric length × 100

  • Tex to Ne

    Ne = 590.5 / tex

  • Denier to tex

    tex = denier / 9

  • Thread density

    EPI (ends per inch) × PPI (picks per inch)

1

Topic 1

Yarn numbering systems

ComparisonCount systems
Indirect (length per weight)
Direct (weight per length)

Principle

Higher number = finer yarn

Higher number = coarser yarn

Examples

English cotton count Ne (840-yard hanks per lb), metric Nm (km per kg), worsted count (560-yard hanks per lb)

Tex (g per 1,000 m), denier (g per 9,000 m), decitex (g per 10,000 m)

Used for

Spun yarns — cotton, wool

Filaments and man-made fibres

Key formulasConversions

  • Ne to tex

    Tex = 590.5 ÷ Ne

  • Nm to tex

    Tex = 1,000 ÷ Nm

  • Denier to tex

    Tex = denier ÷ 9

  • Ne to Nm

    Nm = 1.693 × Ne

  • Ne to denier

    Denier = 5,315 ÷ Ne

  • Resultant count of ply yarn (indirect)

    1 ÷ R = 1 ÷ N1 + 1 ÷ N2 (2/40s = 20s resultant)

Example

Ne 20 → tex = 29.5; denier = 266. A 2/60s ply yarn has a resultant of 30s.

2

Topic 2

Effect of yarn count on cost and performance

  • Finer yarns (higher Ne): need better (longer, finer) fibres and more spinning time → costlier; give lighter, smoother, softer fabrics with better drape but lower abrasion resistance. Coarser yarns: cheaper, stronger per yarn, heavier and more durable — denim, canvas, towels.
3

Topic 3

EPI and PPI with a pick glass

  • EPI (ends per inch): warp threads per inch; PPI (picks per inch): weft threads per inch.
ProcessUsing a pick glass (counting glass)
  1. 1Lay fabric flat; place the pick glass with its 1-inch (or 1 cm) opening aligned with the warp
  2. 2Count the ends inside the frame with a needle
  3. 3Rotate 90° and count picks
  4. 4Repeat at three to five places; take the average
  5. 5Express as EPI × PPI, e.g., 132 × 72
  • Fabric construction is written as warp count × weft count / EPI × PPI, e.g., 40s × 40s / 132 × 72 (a poplin).
4

Topic 4

Crimp

  • Crimp: waviness of yarns as they pass over and under each other; the yarn removed from fabric is longer than the fabric.
Key formulasCrimp

  • Crimp %

    (Yarn length − fabric length) ÷ fabric length × 100

  • Yarn length

    Fabric length × (1 + crimp ÷ 100)

Example

A 20 cm strip yields a warp yarn 21.6 cm long when straightened: crimp = 1.6 ÷ 20 × 100 = 8%.

5

Topic 5

Fabric weight (GSM)

Key formulasGSM

  • Direct method

    Cut a 100 cm² sample with a GSM cutter; weigh in grams × 100

  • From construction (approx.)

    GSM = [(EPI × 39.37 ÷ Ne × (1 + warp crimp)) + (PPI × 39.37 ÷ Ne × (1 + weft crimp))] × 0.5905

  • Ounces per square yard

    oz/yd² = GSM ÷ 33.9

  • Linear weight

    Grams per running metre = GSM × width in metres

Example

A 100 cm² sample weighs 1.45 g → GSM = 145. Denim of 400 GSM ≈ 11.8 oz per square yard.

  • Global expressions: GSM (most countries), ounces per square yard (denim, USA), grams per linear metre, momme (silk — 1 momme ≈ 4.3 GSM).

Key terms

Indirect count
Count where higher numbers mean finer yarn
Tex
Grams per 1,000 metres of yarn
EPI and PPI
Ends and picks per inch
Crimp
Waviness of yarn in fabric
GSM
Grams per square metre of fabric

Quick revision

  • Ne, Nm, worsted (indirect); tex, denier, decitex (direct); conversions; ply resultant.
  • Finer count = costlier, lighter, smoother.
  • Pick glass method; construction notation.
  • Crimp % formula.
  • GSM by cutter and calculation; oz/yd²; momme.

Important exam questions

Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).

Short-answer questions

  1. Q1.Convert Ne 30 to tex.
  2. Q2.Which system is direct: Ne or denier?
  3. Q3.What is the resultant count of 2/40s?
  4. Q4.Write the construction notation of a fabric.
  5. Q5.Define crimp.
  6. Q6.Convert 200 GSM to oz per square yard.

Long-answer questions

  1. Q1.Explain direct and indirect yarn numbering systems with conversions.
  2. Q2.Explain how to determine EPI, PPI and crimp.
  3. Q3.Explain the calculation and expressions of fabric weight.

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