FIBC Bulk Bag Fabric: Body, Top, Bottom & Spout Area, Fabric Mass and Bag Tare

The formula

This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.

How the result is derived

Step by step, from the values you type to the figure on screen.

1. The 15 inputs are read from the form on every keystroke: Base Length, Base Width, Body Height, Vertical Body Seams, Seam Allowance per Edge, Filling Spout Diameter (0 = None), Filling Spout Length, Discharge Spout Diameter (0 = None), Discharge Spout Length, Base Fabric Weight, Coating or Lamination Weight (0 = Uncoated), Lifting Loops, Webbing Length per Loop, Webbing Weight and Safe Working Load.
2. Each value is checked against the accepted range in the input table below. A value outside its range stops the calculation rather than producing a misleading figure — the results blank out and a message appears.
3. The validated values are substituted into the expression above, which resolves Bag Tare (Fabric + Loops) together with every supporting figure in one pass — no value is carried over from a previous entry.
4. The supporting outputs — Body Fabric, Top and Bottom Panels, Spouts, Fabric per Bag, Outer Faces of the Bag (for Comparison), Fabric Mass incl. Coating, Loop Webbing Mass, Tare as a Share of SWL and Bags per Tonne of Coated Fabric — come from the same pass, so they always describe the same case as the headline figure.
5. Results are rounded for display only. The full-precision value is used throughout the chain, so reading a rounded intermediate figure back into the tool by hand can shift the last digit.

What each input means

Where to read each value on the floor, the unit it must be in, and the range the tool accepts.

What the tool returns

The headline figure and every supporting value it is built from.

Worked example

Substituting

The outer faces are 5.22 m². Seams, hems and two spouts add 1.74 m² more, a third again.

How to use it

1. Work through the input groups in order — Bag Dimensions and Fabric, Loops & Load. The defaults are a realistic case, so you can change one value at a time and watch what moves.
2. 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.
3. Read Bag Tare (Fabric + Loops) in the dark results panel — that is the headline figure, expressed in kg.
4. Check the supporting rows underneath (Body Fabric, Top and Bottom Panels, Spouts, Fabric per Bag, Outer Faces of the Bag (for Comparison), Fabric Mass incl. Coating, Loop Webbing Mass, Tare as a Share of SWL and Bags per Tonne of Coated Fabric) before acting on the headline — they are where an implausible input usually shows itself first.
5. 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

• Process planning — establishing Bag Tare (Fabric + Loops) before a trial is booked, so machine time and material in Nonwovens & Technical Textiles are committed against a calculated figure rather than an estimate.
• Costing and quotation — Bag Tare (Fabric + Loops) is an input to the cost sheet, and quoting from a worked number rather than a remembered one is what keeps a margin intact.
• Troubleshooting — when the floor result drifts from plan, entering the measured values (starting with Base Length) shows how much of the gap in Bag Tare (Fabric + Loops) each variable explains.
• Teaching and study — the accepted ranges bracket normal Nonwovens & Technical Textiles practice, so moving one variable at a time shows the shape of the relationship rather than a single answer.

Reading the result

Typical bands and what each one is telling you.

Assumptions and limits

• Every dimension and weight is the bag specification's; the tool has no typical figure of its own. The body is a tube the height of the bag plus a seam allowance top and bottom, with an allowance on each side of every vertical seam; a circular woven body has none. Top and bottom panels are counted flat with an allowance round each edge, and spouts as plain cylinders, so a duffle top, a cone bottom or a baffle bag needs its extra fabric added. Thread, labels, document pouches, liners and fabric lost in cutting are not counted, so a weighed bag comes out heavier. **This is a fabric and mass estimate, not a safety rating: the safe working load and the safety factor come from the bag's own type test.**
• Every input is bounded to the range normal practice occupies (Base Length 20 to 300 cm, Base Width 20 to 300 cm and Body Height 20 to 400 cm, 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 21898, Packaging, Flexible intermediate bulk containers (FIBCs) for non-dangerous goods: design type tests and the marking of safe working load and safety factor.
• For dangerous goods, the UN Recommendations on the Transport of Dangerous Goods and national rules such as 49 CFR 178, which set the FIBC type tests.
• The bag's own specification sheet, which sets the dimensions, fabric and coating weights, and loop construction.

Questions people ask