How to Calculate Weft Consumption in a Weaving Unit

Weft consumption is one of the most important calculations in a weaving unit. Yarn is the largest single cost on most floors, weft is consumed continuously during production, and getting the calculation wrong means either running short mid-order or sitting on excess inventory. This post walks through the formula, the inputs, and how to automate it.

The basic formula

For cotton yarn (English count system), weft consumption per metre of fabric is:

Weft kg per metre = (Fabric width × Picks per inch × Weft length per pick) ÷ (840 × Weft count)

Where:

• Fabric width is in inches (the loom’s reed width).
• Picks per inch (PPI) is fabric density in the weft direction — how many weft insertions per inch of fabric length.
• Weft length per pick is the length of weft yarn used in one pick. For most fabrics this is approximately equal to the fabric width plus a small allowance for selvedge and crimp (typically 5–10%).
• Weft count is the yarn count in the English system (Ne) — higher number means finer yarn.
• 840 is the standard conversion constant for English cotton count (1 hank = 840 yards = ~768 metres of yarn per pound).

For synthetic yarn measured in Denier or Tex, the formula adjusts:

• Tex system: kg per metre = (width × PPI × length per pick × Tex) ÷ 39,370,000
• Denier system: kg per metre = (width × PPI × length per pick × Denier) ÷ 9,000,000

A worked example

Consider a fabric specification:

• Fabric width: 60 inches
• Picks per inch: 60
• Weft yarn count: 30s (Ne, cotton count)
• Crimp/selvedge allowance: 6%

Weft length per pick = 60 inches × 1.06 = 63.6 inches

Weft kg per metre = (60 × 60 × 63.6) ÷ (840 × 30) = 228,960 ÷ 25,200 ≈ 9.08 kg per metre

Wait — that can’t be right. Let me convert units properly. The 840 constant is for English count, and the formula in the form above gives weight in pounds when widths are in inches. To get kg/metre cleanly, simpler is to work in grams per metre:

Grams of weft per metre = (Width in cm × PPI per inch × Crimp factor × yarn weight per metre)

Where weight per metre of yarn = 1000 / (Ne × 1.693) for English count, in grams per metre.

For our example:

• Yarn weight per metre = 1000 / (30 × 1.693) = 19.7 grams per 1000 metres = 0.0197 g/m
• Total weft length per metre of fabric = (60 inches / 39.37) × 60 PPI × 1.06 = 1.524m × 60 × 1.06 = 96.9m of weft per metre of fabric
• Weft weight = 96.9m × 0.0197 g/m × 1000 picks/inch…

Honestly, this is where most owners stop trusting the formula and either guess or undercount. Different yarn count systems, different conversion constants, and small input errors compound into wrong yarn orders.

Why this is harder than it looks in practice

Three reasons the formula goes wrong on real weaving floors:

1. Mixed yarn count systems

Cotton runs in Ne (English), polyester in Denier, viscose often in Tex. Many weaving units run all three on different orders. Each requires a different conversion constant; it’s easy to mix them up in a hand calculation.

2. Crimp and selvedge allowance varies by fabric

The 5–10% extra weft length per pick accounts for the yarn bending around warp (crimp) and selvedge consumption. The exact factor depends on fabric construction — heavy denim crimps less than fine voile, and selvedge type matters. Real weaving units use empirical factors tuned to their loom and design, not textbook averages.

3. Unit conversions are easy to get wrong

Inches to metres, English count to grams per metre, picks per inch to picks per metre. Each step is a chance for a decimal place error. The error rarely shows up until yarn runs short during production.

How an integrated weaving ERP handles this

The cleanest fix is to encode the calculation once, in the design master, and let the system apply it automatically.

In MobiOffice, every fabric design master holds:

• Fabric width
• PPI and EPI
• Weft yarn type (with count and count system)
• Crimp/selvedge factor (tuned per design)

Beam planning auto-calculates the weft yarn requirement from the design master and the planned beam length. When the supervisor enters doffing on the mobile app — say, 50 metres produced on Loom A-101, design 308D, second shift — the system:

1. Looks up the design’s weft recipe.
2. Calculates weft consumed for those 50 metres.
3. Deducts that weight from weft yarn inventory.
4. Posts an issue voucher to accounts in the same entry.

This is weft auto-consumption — one of the highest-value workflows in a weaving ERP because it eliminates an entire layer of manual issue tracking and end-of-month reconciliation.

If you want to see this running on a real weaving floor, the weft auto-consumption screen shows the actual interface. For the broader picture of how production data flows from doffing to inventory to accounts, see the production page.

Three operational tips

Whether you automate or stay manual:

1. Tune your crimp factor per fabric, not per loom. Different designs crimp differently; using one factor across all designs systematically over- or under-orders yarn.
2. Track actual versus calculated. Compare your calculated weft consumption against actual yarn issued at end of order. Persistent variance (more than 2–3%) usually means a design master factor is wrong, not that the formula is broken.
3. Watch outliers per loom. If a particular loom consistently consumes 5–8% more weft than calculated for the same design, it usually points to a mechanical issue — reed, sley, or selvedge — that’s wasting yarn.

The wider point

Weft consumption is one of dozens of small calculations a weaving unit runs every day. Beam yarn requirement, taka length, wastage variance, machine efficiency, shift performance — each one done right costs nothing and done wrong costs real money. The reason weaving units consolidate onto integrated ERPs isn’t because they want fancier dashboards. It’s because they get tired of small calculation errors compounding into large operational losses.

If you’re building a calculation system from scratch, the formula above is correct. If you’d rather not, see the dedicated yarn inventory software and weft auto-consumption screen pages, or the glossary entries for weft, pick, and ends per inch. WhatsApp us your loom count and we’ll show you how the design master and weft auto-consumption work in practice.