Curtain-Sided Trailer Curtains: Cut Size, Fabric Widths, Fabric Bought, Mass & Straps

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 9 inputs are read from the form on every keystroke: Body Length, Side Opening Height, Curtains, Wrap round the End Pole, Each End, Top Fixing Allowance, Bottom Hem & Strap Pocket, Fabric Roll Width, Fabric Weight and Strap Spacing.
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 Fabric to Buy together with every supporting figure in one pass — no value is carried over from a previous entry.
4. The supporting outputs — Cut Length, Cut Height, Roll Widths per Curtain, Fabric Length off the Roll, Fabric in the Curtains, Bought Fabric Trimmed Away, Curtain Set Mass (Fabric) and Tensioning Straps — 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

With 3 m fabric each curtain is one width: 85.2 m² bought instead of 142.

How to use it

1. Work through the input groups in order — Body and Fabric & Straps. 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 Fabric to Buy in the dark results panel — that is the headline figure, expressed in m².
4. Check the supporting rows underneath (Cut Length, Cut Height, Roll Widths per Curtain, Fabric Length off the Roll, Fabric in the Curtains, Bought Fabric Trimmed Away, Curtain Set Mass (Fabric) and Tensioning Straps) 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 Fabric to Buy before a trial is booked, so machine time and material in Leather, Coated Fabrics & Tarpaulins are committed against a calculated figure rather than an estimate.
• Costing and quotation — Fabric to Buy 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 Body Length) shows how much of the gap in Fabric to Buy each variable explains.
• Teaching and study — the accepted ranges bracket normal Leather, Coated Fabrics & Tarpaulins 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

• Each curtain is one piece running the length of the body, wrapped round the end poles, with the top fixing allowance and a bottom hem for the strap pockets. When the cut height is more than one roll width, widths are welded along the length, and the trimmed edge of the last width is bought but not used. Dimensions, allowances, fabric and strap spacing are yours or the body builder's. Mass is the fabric in the curtains; straps, buckles, rollers and weld overlaps are extra. **Curtains are not load restraint unless the body is certified for it; secure the load as the body's rating and the load securing rules require.**
• Every input is bounded to the range normal practice occupies (Body Length 1 to 20 m, Side Opening Height 0.5 to 4 m and Curtains 1 to 4 curtains, 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

• EN 12642, Securing of cargo on road vehicles, body structure of commercial vehicles: the body ratings that say whether curtains count towards load restraint.
• The coated fabric data sheet: weight, tensile and tear strength and coating.

Questions people ask