RFQ Tracker
Track quotations, due dates, customer communications, and RFQ status from one dashboard.
Coil ID Calculator
Calculate coil inner diameter (bore) from weight, OD, strip width, and material density. Verify mandrel compatibility before loading coils on your decoiler.
Ready to Quote This Job?
After calculating material requirements, many manufacturers track RFQs, due dates, customer communications, and quotation status using the RFQ Tracker.
Manufacturing Workflow
Most manufacturing jobs follow a simple workflow: calculate material requirements, estimate costs, prepare quotations, and track RFQs. The tools below help manage each stage.
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Steel Weight Calculator
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Coil Weight Calculator
Calculate coil weight from OD, ID, strip width, and material density.
Coil Thickness Calculator
Back-calculate strip thickness from coil weight, OD, ID, and width.
Coil Length Calculator
Determine total strip length from weight, thickness, and width.
Coil OD Calculator
Calculate outer diameter from weight, ID, width, and density.
Coil Width Calculator
Calculate strip width from coil weight, OD, ID, and density.
Material Cost Calculator
Calculate raw material cost, cost per part, scrap cost, and total batch cost for manufacturing.
Once material quantities and costs are calculated, the next step is managing customer RFQs, quotation deadlines, and communications. The RFQ Tracker helps organize the entire quotation process from enquiry to submission.
How to Calculate Coil Inner Diameter
The coil ID calculator determines bore diameter from: ID = √(OD² − (4 × Weight × 1e9) ÷ (π × Width × Density)). This is essential when incoming coils are banded and the bore is inaccessible for direct measurement. By weighing the coil and measuring OD externally, you can verify that the ID matches your decoiler mandrel before committing crane time to loading.
A coil with unexpected ID means it cannot mount on the intended mandrel—508 mm ID won't fit a 610 mm mandrel, and vice versa. Early detection through calculation prevents failed loading attempts that waste crane availability and operator time.
Standard IDs and Mandrel Compatibility
Industry uses three standard IDs: 405 mm (16") for narrow strip, 508 mm (20") for most cold-rolled automotive and general manufacturing (70% market share), and 610 mm (24") for heavy-gauge hot-rolled. Expandable mandrels cover a range—a "508 mm mandrel" typically grips 490–530 mm. Confirm your mandrel's expansion range covers the supplier's actual ID spec.
ID Effect on Strip Quality
Smaller IDs create tighter inner-wrap curvature, causing coil set (residual curve). Bending strain = Thickness ÷ ID. A 2.0 mm strip on 405 mm ID reaches 0.5% strain—near yield for mild steel, causing permanent set on inner wraps. For gauges above 2.0 mm, specifying 610 mm ID reduces leveling requirements and minimizes scrap wraps from coil interiors.
Frequently Asked Questions
How do you calculate coil inner diameter?▼
ID = √(OD² − (4 × Weight × 1e9) ÷ (π × Width × Density)). Rearranges the weight formula to solve for ID from OD, weight, width, and density.
What are standard coil inner diameters?▼
Standard IDs: 405 mm (16"), 508 mm (20"), and 610 mm (24"). The 508 mm is most common—approximately 70% of cold-rolled coils use this size.
Why does coil ID matter for decoiler selection?▼
The decoiler mandrel must match the coil ID. A 508 mm ID coil can't mount on a 610 mm mandrel. Expandable mandrels typically cover 450–530 mm or 490–610 mm ranges.
Can I calculate ID from coil weight and OD?▼
Yes. Enter weight, OD, strip width, and material density. The calculator solves for ID without needing bore access.
How does ID affect coil weight?▼
Larger ID = less material for same OD. A 610 mm ID coil weighs less than 508 mm ID at identical OD, width, and gauge because the bore displaces metal volume.
What happens if I use wrong ID in calculations?▼
ID appears as a squared term—100 mm error on a 1800 mm OD coil causes 5–8% weight miscalculation. Always verify ID from purchase orders or mandrel specs.
How do I measure coil ID?▼
Insert caliper or folding rule into bore. For banded coils where bore is inaccessible, use mandrel spec from mill certificate or purchase order.
Does coil ID affect strip quality?▼
Yes. Smaller IDs create tighter curvature, increasing coil set (residual curve) on inner wraps. 405 mm ID coils need more leveling than 610 mm ID.
Can different IDs be used on same line?▼
Yes, with expandable mandrels. But switching requires adjustment and verification. Many plants standardize on 508 mm to avoid changeovers.
What ID should I specify when ordering?▼
Match your decoiler mandrel spec. If mandrel expands 490–530 mm, order 508 mm ID. Mismatched ID means coil cannot be loaded.