Garments consumption is one of the most important parts of costing.
A small mistake in consumption can change the final price of a garment — making your costing incorrect.

But here is the secret:

If you can correctly calculate Length and Width, then fabric consumption becomes extremely easy.
This is what I call the Magic Formula.

However, you must practice regularly to calculate perfectly.

Why Two Methods? (Side Seam & Inseam)

For basic trouser / pant / leggings, consumption can be calculated in two different ways, depending on the measurement chart:

• Some charts use Side Seam Length
• Some charts use Inseam Length

So you must learn both.

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1️⃣ Consumption Using Side Seam Length

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We calculate in two scenarios:

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➤ A) Side Seam = Including Waistband

✔ Length Formula

Length = Side Seam (with waistband)
       + 3 cm allowance (2 cm hem fold + 1 cm sewing)
       + Waistband Height
       + 1 cm sewing allowance

✔ Width Formula (Updated)

Width = (Thigh Measurement + 2)  2 cm sewing allowance

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➤ B) Side Seam = Excluding Waistband Height

✔ Length Formula

Length = Side Seam (excluding waistband)
       + 4 cm allowance (1 cm join with waistband + 2 cm hem fold + 1 cm sewing)
       + Waistband Height × 2 (because waistband is double folded)
       + 2 cm allowance 

✔ Width Formula

Width = (Thigh Measurement + 2)  2 cm sewing allowance

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2️⃣ Consumption Using Inseam Length

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Two more scenarios:

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➤ A) When Rise = Including Waistband

Take the bigger measurement between Back Rise and Front Rise.

✔ Length Formula

Length = Inseam
       + 3 cm allowance (hem fold + sewing)
       + Bigger Rise (Front/Back)
       + Waistband Height
       + 1 cm sewing allowance

✔ Width Formula (Updated)

Width = (Thigh Measurement + 2)  2 cm sewing allowance

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➤ B) When Inseam = Excluding Waistband Height

✔ Length Formula

Length = Inseam
       + 3 cm allowance
       + Bigger Rise (Front/Back)
       + 1 cm allowance (join with waistband)
       + Waistband Height × 2 (because waistband is double folded)
       + 2 cm allowance 

✔ Width Formula (Updated)

Width = (Thigh Measurement + 2)  2 cm sewing allowance

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⭐ Final Fabric Consumption Formula

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After Length and Width are ready:

Final Consumption (kg/dozen) 
= (Length × Width × 4 × GSM × 12) / 10,000,000 
  + Wastage %

✔ Why multiply by 4?

A trouser has 4 panels:

• Left Front
• Left Back
• Right Front
• Right Back

✔ Why multiply by 12?

To convert per piece consumption → per dozen.

✔ Why divide by 10,000,000?

To convert cm² → m² and grams → kilograms.

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⭐ GSM Explained (Simple Way)

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GSM = Grams Per Square Meter
It indicates the weight of fabric per square meter.

• Higher GSM → thick/heavy fabric
• Lower GSM → light fabric

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⭐ Why Wastage Is Necessary

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Wastage is unavoidable, so we always add a wastage %.

1. Cutting Wastage

Cutting tables always generate wastage because:

• Fabric is cut from a tubular roll, so the GSM measured at dyeing may slightly change
• Some fabric is unusable from the roll head or tail
• Many small fabric scraps are created
• Sometimes fabric rejection happens and replacement cutting is needed

2. Sewing Wastage

During sewing:

• Alterations may be needed
• Some panels can be rejected
• Stitching mistakes create extra wastage

3. Finishing Wastage

In finishing:

• Panels shrink
• Stains or defects appear
• Some garments fail final inspection

Final Reason for Adding Wastage

A garment is made by many people across many departments — cutting, sewing, finishing, QC, packing.
So the total output is never equal to the total cutting quantity.
For safe and accurate costing, wastage must always be added.

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Conclusion

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Trouser, Pant, Leggings consumption becomes extremely simple when you know:

Length + Width = Accurate Fabric Consumption

The Magic Formula works 100% when practiced daily.