Steel coil calculator
The steel coil calculator converts the full set of coil parameters: weight, strip length, outer diameter, winding height and weight per millimetre of width. One known value is enough, the others are calculated automatically in both directions, so it is just as quick to check the weight of a coil with a given diameter as the diameter of a coil with a given weight.
| Coil weight | - |
|---|---|
| Strip length | - |
| Outer diameter | - |
| Winding height (coil wall thickness) | - |
| Weight per 1 mm of width | - |
| Strip surface area (one side) | - |
The coil is calculated, now it is time to choose the material
Coil parameters translate directly into cost: the strip width determines the amount of longitudinal waste, the thickness determines the length of material on the coil, and the outer diameter and weight decide whether the coil will fit on the line and on the truck at all. HEN-STOL supplies steel sheets without a mill certificate: hot-rolled, cold-rolled and galvanized, in coils, slit strips and sheets cut to length from coil, in second grade (non-prime), as well as overrolled steel and overproduction at attractive prices. Just send the grade, thickness, width and approximate coil weight, and we will get back to you with an offer.
How the calculator converts coil parameters
1. Weight per 1 mm of width. All results are derived from one intermediate value: the weight per millimetre of strip width. When the coil weight is entered, it is the coil weight divided by the strip width; when the length is entered: length [m] × thickness [mm] × 7.85 / 1000.
2. Strip length. length [m] = weight per 1 mm / thickness [mm] / 7.85 × 1000. The same mass of steel gives a longer strip the thinner the sheet.
3. Outer diameter. outer diameter [mm] = 2 × square root of (weight per 1 mm / π / 7.85 × 1,000,000 + inner diameter² / 4). The formula follows from the area of the ring formed by the wound strip in the coil cross-section.
4. Winding height. winding height [mm] = (outer diameter - inner diameter) / 2. This is the coil wall thickness, the parameter that most often limits the decoiler and the spread of the crane arms.
The calculations are based on a specific weight of 7.85 kg/dm³ for steel and stainless steel and on π = 3.1416, and the results are rounded to whole kilograms, metres and millimetres.
The same coil at different sheet thicknesses
Overview for a coil weighing 10,000 kg, with a strip width of 1250 mm and an inner diameter of 610 mm, calculated with the same formula as the calculator.
| Thickness | Strip length | Outer diameter | Winding height |
|---|---|---|---|
| 0.5 mm | 2,038 m | 1,292 mm | 341 mm |
| 1.0 mm | 1,019 m | 1,292 mm | 341 mm |
| 1.5 mm | 679 m | 1,292 mm | 341 mm |
| 2.0 mm | 510 m | 1,292 mm | 341 mm |
| 3.0 mm | 340 m | 1,292 mm | 341 mm |
The outer diameter and winding height stay the same, because the size of the coil is determined by the mass of steel per millimetre of width, not by the strip thickness. The thickness does, however, change the length of material on the coil, i.e. the number of parts that can be produced between one line changeover and the next.
What determines coil dimensions in practice
The inner diameter results from the coiler standard at the rolling mill and from the customer's equipment. Coils with an inner diameter of 508 mm and 610 mm are the most common, 762 mm less so. At the same weight, a larger inner diameter means a larger outer diameter, because the same amount of steel is spread over a larger circumference.
The second limitation is the winding height and outer diameter compared with the capacity of the decoiler, the cut-to-length or slitting line and the clearance of the hall. The third is the lifting capacity of the crane and the permissible axle load in transport, which is why typical commercial coils usually weigh from a few to a dozen or so tonnes.
It is worth remembering that the actual weight of a coil delivered from the mill differs slightly from the calculated one, because the sheet has thickness and width tolerances, and the specific weight of a particular grade may differ minimally from the assumed 7.85 kg/dm³.
Coil, strip and sheet in one order
The coil is the starting material. Slitting produces strips of a given width, and cutting to length produces sheets of a given length, and each of these operations changes the cost structure and the amount of waste. The coil calculator makes it possible to estimate how much material a coil contains before deciding on the format, and further calculations are easier with the sheet metal weight calculator and the sheet metal waste calculator.
Frequently asked questions about steel coil weight and dimensions
How is the weight of a steel coil calculated?
The coil weight is the area of the ring in the cross-section multiplied by the strip width and the specific weight of steel: weight [kg] = (outer diameter² - inner diameter²) × π / 4 × width [mm] × 7.85 / 1,000,000. In the calculator, entering the outer diameter is enough and the weight is calculated automatically.
How is the strip length in a coil calculated?
The length follows from the weight, width and thickness: length [m] = weight [kg] / (width [mm] × thickness [mm] × 7.85) × 1000. For a 10-tonne coil with a width of 1250 mm and a thickness of 2 mm, this gives 510 m of strip.
What is the typical inner diameter of a coil?
In commercial trade, coils with an inner diameter of 508 mm and 610 mm are the most common, 762 mm less so. The inner diameter affects the outer diameter and the winding height, so when comparing offers it is worth stating it together with the weight and width.
Does the calculator also work for stainless steel?
Yes, with a specific weight of 7.85 kg/dm³. For some stainless grades the actual specific weight is slightly higher, so the result for stainless steel should be treated as an approximation with a margin of a few percent.
Is the calculator result enough to order a coil?
The result is a good starting point for discussing the material and for checking whether the coil will fit on the line. The final parameters depend on the available stock, tolerances and cutting options, so the quickest way is to send the grade, thickness, width and approximate coil weight in an enquiry.