In the early stages of a plant project, you often need to estimate equipment costs without detailed quotes. The Six-Tenths Rule is a simple and fast way to do this.
Even if you’re a beginner in engineering or project planning, you can use this rule to get a rough cost idea based on equipment size.
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What Is the Six-Tenths Rule?
The Six-Tenths Rule (also written as the 0.6 exponent rule) says:
Cost₂ = Cost₁ × (Size₂ / Size₁)^0.6
This means that when the size of equipment increases, the cost increases—but not in a straight line.
Instead, costs grow more slowly than size, thanks to economies of scale.
When Is This Rule Useful?
This rule helps when you:
- Don’t have a supplier quote yet
- Need a quick estimate for budgeting
- Want to compare equipment sizes
Example:
If a 1,000 L reactor costs $100,000, a 2,000 L reactor would cost:100,000 × (2,000 / 1,000)^0.6 ≈ $151,000
Notes for Batch Chemical Plants
In batch-type chemical plants, equipment sizes and usage vary more than in continuous plants.
So, the Six-Tenths Rule gives only a rough guide—final costs depend on materials, pressure ratings, and special functions.
Still, it’s a good first step when planning.
Conclusion
The Six-Tenths Rule is a helpful tool for early cost estimation.
It’s not exact, but it’s better than guessing. Engineers and planners can use this method to plan smarter and faster.
If you’re new to plant design or project work, keep this rule in your toolbox!