Engineering Unit Converter

Convert common engineering units: MPa to ksi, mm to inches, g/cm³ to lb/in³, and more.

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How to Use

  1. 1
    Select the Measurement Category and Unit to Convert From

    Choose the physical quantity category (stress, pressure, force, length, temperature, energy, or toughness) and select the source unit from the dropdown menu.

  2. 2
    Enter the Value to Convert

    Type the numeric value in the input field; the converter accepts scientific notation (e.g., 2.5e6) for very large or small values.

  3. 3
    Read the Converted Value in Your Target Unit

    All equivalent values across the unit family are displayed simultaneously, allowing you to read any target unit without performing the conversion multiple times.

About

Engineering work increasingly crosses international boundaries, and the coexistence of SI (metric) and US customary unit systems means that unit conversion is a daily requirement for any engineer working with international codes, supplier datasheets, or multi-national project teams. Errors in unit conversion have contributed to notable engineering failures, including the Mars Climate Orbiter loss in 1999, caused by a mismatch between pound-force·second and Newton·second units.

The AlloyFYI Unit Converter is specialized for the quantities most relevant to materials and structural engineering: stress, strain, pressure, force, energy (including impact toughness), fracture mechanics parameters, temperature, thermal conductivity, and specific heat. Unlike generic unit converters, the tool displays all common units in the category simultaneously rather than requiring the user to perform multiple conversions, and provides engineering-relevant reference values for context.

FAQ

What are the most common unit conversions needed in alloy engineering?
Stress and pressure conversion between MPa (SI), ksi (US customary), and psi is the most frequent requirement, since material datasheets, design codes, and specification documents span all three systems. Hardness conversion (HV, HRC, HBW, HRB) is also very common, as measurement equipment, inspection reports, and design limits may use different scales. Fracture toughness (MPa√m and ksi√in), impact energy (Joules and ft·lbf), and temperature (°C, °F, K) complete the set of conversions needed daily by practicing materials and mechanical engineers working on international projects.
How do I convert psi to MPa and vice versa?
1 MPa = 145.038 psi, so to convert psi to MPa, divide by 145.038, or equivalently multiply by 0.006895. To convert MPa to psi, multiply by 145.038. For rapid mental arithmetic, note that 100 MPa ≈ 14,500 psi and 1 ksi (1,000 psi) ≈ 6.895 MPa. Common benchmarks: structural steel yield strength 250 MPa ≈ 36.3 ksi; aerospace aluminum 7075-T6 tensile strength 572 MPa ≈ 83 ksi; gas turbine blade operating stress 200 MPa ≈ 29 ksi.
Why are there different 'tons' in materials testing (metric ton, short ton, long ton)?
The metric ton (tonne) = 1,000 kg = 2,204.6 lb is the SI-consistent unit of mass widely used internationally. The short ton (US ton) = 2,000 lb = 907.2 kg is used in the United States for raw material pricing and capacity specifications. The long ton (UK ton) = 2,240 lb = 1,016 kg was historically used in British engineering. Confusion between these units in tensile test loads, press capacities, or ship displacement calculations has caused significant errors; the SI unit (metric ton or kilonewton) should always be preferred in international engineering documents.
What is the relationship between Joules (J) and foot-pounds (ft·lbf) in Charpy testing?
1 J = 0.7376 ft·lbf (foot-pound force), so to convert Charpy impact energy from J to ft·lbf, multiply by 0.7376. ASTM E23 Charpy impact testing is performed in the United States using ft·lbf units, while ISO 148-1 (the international equivalent) uses Joules. A common low-temperature toughness requirement of 27 J at −20°C (ISO) corresponds to approximately 20 ft·lbf at −4°F (ASTM). Verification that the correct unit system is applied when transposing Charpy requirements between ASTM and ISO procedures is critical to structural integrity assessment.
How do I convert fracture toughness between MPa√m and ksi√in?
1 MPa√m = 0.9099 ksi√in. To convert ksi√in to MPa√m, multiply by 1.099. Common benchmarks: high-strength aerospace aluminum 7050-T7451 has K_IC ≈ 34 MPa√m (31 ksi√in); structural steel A36 has K_IC ≈ 80–100 MPa√m (73–91 ksi√in); 4340 steel at 1,400 MPa yield has K_IC ≈ 60 MPa√m (55 ksi√in). Note that the mixed units of fracture toughness (Pa√m) arise because stress intensity factor has dimensions of stress×√length, a direct consequence of the singular stress field at a crack tip.
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