Cast Iron Weight Calculator (Gray & Ductile)
Calculate gray or ductile iron casting weight by grade and class — the only cast-iron calculator that uses class-dependent densities instead of a single hard-coded value. Density varies measurably across iron classes (about 7.05–7.30 g/cm³), which matters on large castings. Includes 8 shapes, CAD-volume input, poured weight and cost.
How cast iron weight is calculated
Weight = volume × density, with the density set by the iron grade you select:
Gray iron density rises with class (more pearlite, less graphite); ductile iron sits around 7.1–7.2. Selecting the right grade avoids a 2–3% weight error.
Cast iron density by grade
| Grade | Class / spec | Density (g/cm³) |
|---|---|---|
| Gray iron | Class 20 / HT150 | 7.05 |
| Gray iron | Class 30 / HT200 | 7.10 |
| Gray iron | Class 40 / HT300 | 7.25 |
| Ductile iron | 60-40-18 / QT400 | 7.10 |
| Ductile iron | 100-70-03 / QT700 | 7.20 |
| Malleable iron | – | 7.27 |
Ranges per AmesWeb / foundry data. Lower-class gray irons (more flake graphite) are lighter.
Frequently Asked Questions
What is the density of gray vs ductile cast iron?
Gray iron ranges from about 7.05 g/cm³ for low classes (Class 20/HT150) up to 7.30 for high classes (Class 50/HT350). Ductile (nodular) iron is about 7.10–7.20. The variation comes from graphite form and content.
How do you calculate cast iron casting weight?
Multiply the casting volume by the grade density. For a round bar, volume = π × (d/2)² × length; multiply by, say, 7.20 g/cm³ for HT250 gray iron to get the weight.
Why does grade/class change the weight?
Higher-class gray irons contain more pearlite and less graphite, so they are slightly denser. Using a single generic 7.2 value can introduce a 2–3% error, which is significant on heavy castings.
Why does my casting weigh more than the machined part?
The as-cast part carries machining allowance, draft and tolerance stock that is later removed. The finished, machined weight is lower than the as-cast weight by the amount of stock removed.
Can I use this for a complex casting?
Yes — switch to Custom Volume and enter the CAD volume directly, or sum several simple shapes. For irregular geometry the CAD volume is the most accurate input.
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