Coil Weight Calculator
Enter the coil outside diameter, inside diameter and width in millimetres and choose the grade. The weight comes from the ring volume and the grade density; a second calculation estimates the number of wraps from the strip thickness.
Coil weight from OD / ID
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 is a ring of strip wound on itself: a hollow cylinder whose outer radius is the coil OD, whose bore is the coil ID, and whose height is the strip width. Multiply that ring volume by the grade density and you have the coil weight. That is the whole calculation, and it is the one used to check a mill packing list, size a crane lift or work out how many coils a truck carries.
The page takes the three coil measurements and the grade. Density comes from the grade table, and the line under the grade says whether it is that grade's own value or a family typical value. Aluminium and stainless coils of the same size differ in weight by a factor of nearly three, so the grade is not a detail here.
The second calculation, approximate turns, divides the radial build-up of the coil by twice the strip thickness. It tells you roughly how many wraps are on the mandrel, which is what a slitting or cut-to-length line wants to know before it schedules the coil. No density is needed for that one.
Show the formula and a worked example
The formula
- coil weight: W = π ÷ 4 × (OD² − ID²) × width × ρ ÷ 10⁹
- approximate turns: n = (OD − ID) ÷ (2 × t)
Dimensions in millimetres, density ρ in kg/m³ — as the engine runs them.
The ring area is π ÷ 4 × (OD² − ID²), the same expression used for a pipe wall but with the whole bore removed. Multiplied by the width it becomes a volume in cubic millimetres; multiplied by density in kg/m³ and divided by 10⁹ it becomes kilograms. The engine keeps full precision and rounds only for display.
The turns estimate is (OD − ID) ÷ (2 × t). Each wrap adds one strip thickness on both sides of the coil, so the radial build-up from ID to OD is the number of turns times twice the thickness. Real coils have a little air between wraps, which is why the answer is called approximate and why a loose coil reads a larger OD than the weight suggests.
The engine refuses a coil whose inside diameter is not smaller than its outside diameter, and any dimension that is zero or negative. A refused input shows a message that says which rule it broke rather than a blank result.
Worked example
| Calculation | Coil weight from OD / ID |
|---|---|
| Outside diameter | 1200 mm |
| Inside diameter | 508 mm |
| Width | 1500 mm |
| Material grade | 1050 |
| Density | 2,710 kg/m³ · grade density |
| Theoretical result | 3,773.5 kg |
Computed by the calculation engine from these inputs at render time, rounded only for display.
Frequently asked
- 01Does the calculation account for the gap between wraps?
- No. It treats the coil as a solid ring, which is what a tightly wound coil is to within a small fraction of a percent. If a coil has telescoped or was rewound loosely, its measured OD grows but its weight does not — measure the OD you have and expect the calculated figure to sit above the scale weight.
- 02Which grade should I pick for a coil marked only by family?
- Pick the generic family entry. The line under the grade will say "family typical value", which is close enough for lifting and transport planning. For a commercial quotation, the confirmed grade sets the density and the mill weight goes on the invoice.
- 03Can I get the coil weight from strip length instead of OD?
- Use the coil length calculator the other way round: it takes weight, width and thickness and returns length, and its second calculation returns the OD a given weight builds on a known ID. Between the two pages you can move from any two of weight, length and OD to the third.
- 04How accurate is the turns figure?
- It is an estimate. Strip thickness runs within a rolling tolerance, and coils are not wound at zero gap, so the count is typically within a few turns of the truth on a coil of several hundred wraps. Use it for scheduling, not for counting.