Coil Length Calculator
Enter the coil weight in kilograms, the strip width and thickness in millimetres and choose the grade. The length comes from the weight divided by the strip's weight per metre; a second calculation returns the outside diameter that weight builds on a known bore.
Coil length from weight
Assumes a tightly wound coil with no gap between wraps. A loose or telescoped coil weighs the same but measures a larger OD.
What this calculates
A coil's weight, its strip cross-section and its density fix the length of strip on it. This page runs that relation: weight ÷ (width × thickness × density) gives metres of strip, which is what a slitter, a roll-former or a cut-to-length line needs to plan blanks and yield from a coil on the packing list.
The second calculation goes to geometry instead. Given the same weight, width and density and a known inside diameter, it returns the outside diameter the coil will have. That answers whether a coil fits an uncoiler, a crane C-hook or a rack slot before it arrives.
Both use the grade density from the table, and the line under the grade says whether the value is the grade's own or a family typical value. Thickness is the nominal strip thickness; strip rolled to the low side of its tolerance carries more length per kilogram than this page shows, and strip rolled thick carries less.
Show the formula and a worked example
The formula
- coil length: L = weight × 10⁶ ÷ (width × t × ρ)
- coil OD from weight: OD = √(ID² + 4 × weight × 10⁹ ÷ (π × width × ρ))
Dimensions in millimetres, density ρ in kg/m³ — as the engine runs them.
Weight per metre of strip is width × thickness × density ÷ 10⁶ with width and thickness in millimetres and density in kg/m³. Length is coil weight divided by that figure, so the engine computes L = W × 10⁶ ÷ (width × t × ρ) and reports it in metres at full precision, rounded only for display.
The OD calculation inverts the coil weight formula. The ring area a given weight needs is W × 10⁹ ÷ (width × ρ), and since that area is π ÷ 4 × (OD² − ID²), the outside diameter is √(ID² + 4 × W × 10⁹ ÷ (π × width × ρ)). The result is a tightly wound OD; loose wraps read larger on the tape.
Every input has to be greater than zero. A zero thickness or width would divide by nothing, so the engine refuses it with a message rather than returning an infinite length.
Worked example
| Calculation | Coil length from weight |
|---|---|
| Coil weight | 5000 kg |
| Width | 1250 mm |
| Thickness | 1.5 mm |
| Material grade | 304 |
| Density | 8,000 kg/m³ · grade density |
| Theoretical result | 333.33 m |
Computed by the calculation engine from these inputs at render time, rounded only for display.
Frequently asked
- 01The mill packing list gives a different length. Which is right?
- The mill measures its strip on the line and weighs the coil on a scale, so its figures include the real thickness and any tolerance. This page uses nominal thickness and the reference density. Treat the two as a cross-check: a large disagreement usually means the thickness on the list is not the nominal one you entered.
- 02Can I use this for aluminium or copper coils?
- Yes. Choose the grade from the aluminium or copper family and the density changes with it. The formula is the same for any strip; only ρ differs.
- 03How do I go from a required length back to a coil weight?
- Multiply the length by width × thickness × density ÷ 10⁶. The coil weight calculator does not take length directly, but the enquiry form does: state the length you need and the grade, and the quotation returns the coil weight and count that covers it.
- 04Why does the OD result assume a tightly wound coil?
- Because the calculation has no way to know the gap between wraps. A coil wound under tension is very close to solid; a rewound or telescoped coil is not. Where the OD matters for an uncoiler, allow a margin above the calculated figure.