Coil Weight and Length: A Worked Arithmetic Example for Aluminum Coil.
Coil weight, strip length and outside diameter are three views of the same arithmetic. If you can move between them with a calculator, you can check a quote, size an uncoiler request and spot a unit mistake before it reaches the purchase order.
Key takeaways
- Mass per meter of strip is thickness times width times density. This post uses 2700 kilograms per cubic meter, a textbook approximation for aluminum.
- Coil weight divided by mass per meter gives approximate strip length. Both move with the actual gauge, so treat results as estimates.
- Outside diameter follows from length, thickness and inner diameter. Winding gaps can make a real coil slightly larger than the estimate.
- Orbit's minimum order is 6.5 MT plus or minus 10 percent, which is 5.85 to 7.15 MT. The length that range covers depends on gauge and width.
Why work the numbers yourself?
Quotes, packing lists and certificates state weight. Your line cares about length, because length decides how long a coil runs before the next change-over, and about outside diameter, because your uncoiler has a limit. The conversion between them is short enough to do by hand, and doing it once catches mismatches that are expensive to find at the dock.
The figures below are arithmetic examples. They are not quotes and do not say which coils Orbit holds. Orbit rolls coil from 0.20 to 2.00 mm thick and up to 1650 mm wide, with an inner diameter of 406 to 508 mm, and coils up to 10 metric tons at maximum width. Coated coil is up to 1.60 mm thick and 1350 mm wide.
What is the formula for strip mass and length?
Work in meters and kilograms. Mass per meter of strip equals thickness in meters, times width in meters, times density in kilograms per cubic meter. For aluminum, 2700 kilograms per cubic meter (2.70 g/cm³) is a textbook value. Alloys differ slightly from it, which is one reason the results are approximate.
A useful shortcut: each millimeter of thickness weighs about 2.7 kilograms per square meter. Length then follows by dividing the coil weight by mass per meter. Keep every width and thickness in the same unit before you multiply, because mixing millimeters and meters gives an answer that is off by a factor of 1000.
How does the arithmetic work for a 0.80 mm by 1000 mm coil?
Take 0.80 mm thickness, 1000 mm width and a 5000 kilogram coil. The arithmetic uses the ordered thickness of the metal. If the coil is coated, the coating adds a small mass that this arithmetic ignores.
| Quantity | Calculation | Result |
|---|---|---|
| Mass per meter of strip | 0.0008 m × 1.0 m × 2700 | 2.16 kg per meter |
| Strip length in the coil | 5000 ÷ 2.16 | about 2315 m |
| Outside diameter | square root of (4 × 2315 × 0.0008 ÷ π + 0.508²) | about 1.62 m |
If the actual thickness is 0.84 mm instead of 0.80 mm, mass per meter becomes 2.268 kilograms and the same 5000 kilogram coil holds about 2205 meters, roughly 110 meters less. A small change in gauge moves length by nearly the same percentage in the opposite direction (5 percent thicker gives about 4.8 percent shorter), which matters when a run is planned in meters.
What does a 10 metric ton coil at 1650 mm wide work out to?
Use 1.00 mm thickness and 1650 mm width as an arithmetic example. Mass per meter is 0.001 × 1.65 × 2700, or 4.455 kilograms. A 10 000 kilogram coil then holds about 2245 meters of strip. With a 508 mm inner diameter, the outside diameter estimate is the square root of (4 × 2245 × 0.001 ÷ π + 0.508²), about 1.77 meters.
Compare that with your own equipment. If your uncoiler accepts a smaller outside diameter or a lower weight, say so in the request. Weight and diameter limits are among the numbers that can rule out a coil, and a supplier can only plan around limits it has been given.
How does the minimum order translate into length?
The minimum order is 6.5 MT, plus or minus 10 percent. That is 5.85 to 7.15 MT. In Example A, 6500 kilograms is about 3009 meters of strip, and the range runs from about 2708 to about 3310 meters.
The same weight is a different length at a different gauge or width, so convert before you decide whether a planned run meets the minimum. Check how the minimum applies to your colors and widths before you plan a run.
What about cut-to-length sheets?
Sheets use the same density. A 0.80 mm sheet 1000 mm wide and 2000 mm long has a volume of 0.0016 cubic meters and weighs about 4.32 kilograms. That gives about 231 sheets per metric ton before any allowance for packing material. If you are weighing sheet against coil for your line, the slit coil and master coil guide covers what each form asks of your equipment.
Which numbers should be stated on the order?
- Alloy, temper and thickness, and whether thickness refers to the metal or the coated product
- Width, and the weight or length basis for the quantity
- Whether stated weights are net or gross
- Your uncoiler's inner diameter, maximum outside diameter and maximum coil weight
Send these in a request for quotation and the arithmetic above can be repeated on the supplier's figures. Orbit answers RFQs within one business day.
Common questions
Which density should I use?
Use 2700 kilograms per cubic meter (2.70 g/cm³) as a textbook approximation. Alloys differ slightly, so treat the results as estimates and rely on the packing list and certificate figures at receiving.
Does the coating change the calculation?
The formulas use the thickness of the metal. A coating adds a thin layer on top, so ask whether the thickness on your order refers to the substrate or to the coated product.
How accurate is the outside diameter estimate?
It assumes tight winding with no gaps between wraps. A real coil can be larger, so compare against the supplier's stated outside diameter and your uncoiler's limit.
What coil weight can Orbit roll?
Rolled coil weight is up to 10 metric tons at maximum width, with an inner diameter of 406 to 508 mm. Send your required coil weight with the request.
References
- Orbit rolled aluminum coil: the rolled coil page, for thickness, width and inner diameter ranges.
- How to read an aluminum coil mill test certificate: for comparing stated weights and dimensions against the order.
Sizing a coil order?
Send alloy, thickness, width, quantity and your uncoiler limits. We respond to RFQs within one business day.