In the world of pressure measurement, two common units stand out: PSI (pounds per square inch) and kilogram-force per square millimeter (kgf/mm²). Whether you’re working in engineering, manufacturing, hydraulics, or automotive design, understanding the difference between these units—and how to convert between them—is crucial. This guide will walk you through the basics, provide the conversion formula, explain where each unit is commonly used, and give you tools to convert PSI to kgf/mm² easily and accurately.
What Is PSI?
PSI (Pounds per Square Inch) is an imperial unit used to measure pressure. It expresses the amount of force in pounds exerted on an area of one square inch.
- Symbol: PSI or psi
- System: Imperial (US customary)
- Usage: Widely used in the United States for measuring tire pressure, hydraulic systems, industrial machinery, and more.
Example: Car tires are often inflated to around 30–35 PSI.
What Is Kilogram per Square Millimeter?
Kilogram-force per square millimeter (kgf/mm²) is a metric unit that measures pressure by expressing the force of one kilogram applied to an area of one square millimeter.
- Symbol: kgf/mm²
- System: Metric (non-SI unit)
- Usage: Commonly used in material science, particularly for tensile strength of metals and high-pressure applications in Europe and Asia.
Example: The tensile strength of steel is often measured in kgf/mm².
PSI vs Kilogram/mm²: Key Differences
| Feature | PSI | kgf/mm² |
|---|---|---|
| Full Form | Pounds per Square Inch | Kilogram-force per Square Millimeter |
| System | Imperial | Metric |
| Scale | Smaller unit | Larger unit |
| Common Use | Automotive, HVAC, hydraulics | Materials testing, heavy industry |
| Region | USA, UK | Europe, Asia |
The Conversion Formula
To convert PSI to kilogram-force per square millimeter (kgf/mm²), use the following formula:
bashCopyEdit1 PSI = 0.07031 kgf/mm²
So, to convert PSI to kgf/mm²:
kgf/mm² = PSI × 0.07031
And to convert kgf/mm² to PSI:
PSI = kgf/mm² ÷ 0.07031
Conversion Examples
Example 1: Convert 100 PSI to kgf/mm²
bashCopyEdit100 × 0.07031 = 7.031 kgf/mm²
Example 2: Convert 5 kgf/mm² to PSI
CopyEdit5 ÷ 0.07031 ≈ 71.11 PSI
PSI to kgf/mm² Conversion Table
| PSI | kgf/mm² |
|---|---|
| 10 PSI | 0.7031 |
| 50 PSI | 3.5155 |
| 100 PSI | 7.031 |
| 200 PSI | 14.062 |
| 500 PSI | 35.155 |
| 1000 PSI | 70.31 |
This table helps visualize how PSI scales up in metric terms.
Why Learn This Conversion?
Understanding how to convert PSI to kgf/mm² (and vice versa) is essential for:
- Engineers and Technicians: International projects often require dual-system understanding.
- Global Manufacturing: Components built in different regions may use different units.
- Academic Use: Engineering exams or research may require unit conversions.
Tips for Easy Conversion
- Use a calculator or online tool: Simply input PSI and multiply by 0.07031.
- Memorize the key value: 1 PSI = 0.07031 kgf/mm²
- Use smartphone apps: Engineering and conversion apps like Unit Converter or Engineering Toolbox.
FAQs
Q1. Is kgf/mm² the same as MPa (Megapascal)?
No, they are different. 1 kgf/mm² ≈ 9.80665 MPa.
Q2. Which is more precise: PSI or kgf/mm²?
Both are precise, but kgf/mm² represents a higher magnitude, often used for extreme pressures or material testing.
Q3. Can I use kgf/mm² in SI units?
No. Although it’s metric, it’s not an SI (International System of Units) unit. The SI equivalent would be the Pascal (Pa).
Conclusion
Both PSI and kgf/mm² are valuable units for measuring pressure in different domains. Knowing how to convert between them is not just a matter of academic interest—it’s a practical skill in today’s globalized engineering and manufacturing sectors. With the simple formula (PSI × 0.07031), you can make fast and accurate conversions anytime.
By understanding the distinctions and conversion process, you can work more effectively across industries and international standards.