Coil Weight, Length and Parts per Coil Calculator for Stamping
Buyers order coils by weight, the press consumes them by length, and the estimator needs parts per coil. This calculator converts between all three from the outside diameter, core size, width and gauge.
Your numbers
Accounts for air between wraps and edge camber. 97 to 99 percent is typical for slit coil.
Feet lost at threading and at the end of the coil.
Your results
Geometric estimate for planning. Actual coil weight on the tag is the reference for receiving and costing.
Coil weight vs outside diameter
Sweeps Coil outside diameter from 30 to 60, holding your other inputs fixed.
Reconcile coil lots against consumption
Optional: see how planned vs actual parts per coil could be tracked from your ERP lot and backflush data.
Optional. The tool and every export work without this. No spam.
How to use it
Measure or read the coil outside diameter and choose the core size. Enter the slit width, gauge and material. The tool returns footage, weight, PIW and parts per coil using your progression pitch. Set a lead and tail allowance for threading and end-of-coil loss. The chart shows how strongly weight rises with outside diameter; because weight grows with the square of the diameter, a few extra inches on a large coil is a lot of steel. Use PIW to check against the uncoiler and cradle rating before you order heavier coils.
Formulas
Coil length in inches equals pi times (OD squared minus ID squared) divided by four, divided by thickness, times a wrap density factor. Weight equals length times width times thickness times density. PIW equals weight divided by width. Parts per coil equals usable length divided by progression pitch, rounded down. Run time equals parts divided by good strokes per hour. All are standard geometric relations; the packing factor is the only empirical term.
- Use the density that matches the alloy; aluminum is about a third of steel.
- Coil set, camber and edge wave reduce the packing factor.
- If the coil is not mill-wound tightly, weigh a sample coil to calibrate the factor.
Common mistakes
Planners often forget the lead and tail loss, which matters on short runs and can leave a coil that is a few hundred parts short of a lot. Another mistake is ordering to a coil weight that the uncoiler cannot hold. A third is treating the core as the same for every supplier; a 16 inch and a 20 inch core change length by several percent. For job costing, compare the calculated weight with the tag weight on receipt and investigate gaps larger than 2 percent.
Frequently Asked Questions
How do I calculate coil length from weight?
Divide weight by width times thickness times density to get length in inches. For a 2,500 lb steel coil, 6 inches wide and 0.060 inch thick, that is about 24,500 inches or roughly 2,040 feet.
What does PIW mean?
Pounds per inch of width. It is coil weight divided by coil width and is the usual capacity rating of uncoilers, cradles and mandrels. Heavy narrow coils can exceed the PIW rating even if total weight looks acceptable.
Why does my actual parts per coil differ?
Typical reasons are lead and tail loss, strip scrapped at splices, camber, a coil that is wound looser than assumed, and reject strips during setup. Track actual parts per coil by lot and tune the allowance and packing factor.
Does this work for aluminum coil?
Yes. Choose the aluminum density. Coil lengths for the same OD, ID and gauge will be the same as steel, but the weight will be about a third, so the PIW limit is less likely to be the constraint.
If coil receipts, lot numbers and consumption are tracked in your ERP, we can add a check that compares planned parts per coil with actual yield per heat or lot.
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