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--SI base value
-The coherent SI unit of this quantityUnits in this list
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| Unit | Value |
|---|
How the converter works
Every unit in a quantity is stored with an exact factor to the coherent SI unit of that quantity. Converting a value takes two steps: multiply by the factor of the unit you start from to get the SI value, then divide by the factor of each target unit. Nothing is converted through an intermediate unit that is not SI, so there is no chain of rounded steps.
- Exact definitions. 1 in = 0.0254 m, 1 lb = 0.45359237 kg and standard gravity g = 9.80665 m/s² are exact by definition. From them: 1 lbf = 4.4482216152605 N, 1 psi = 6894.757293168 Pa and 1 lbf·ft = 1.3558179483314 N·m.
- Temperature. Temperature is the only quantity with an offset. Celsius, Fahrenheit and Rankine convert through kelvin: K = °C + 273.15, K = (°F + 459.67) × 5/9. Temperature differences use the scale factors only (1 K = 1 °C = 1.8 °F).
- Ambiguous units. The converter uses the mechanical horsepower (550 ft·lbf/s), the metric horsepower PS (75 kgf·m/s), the US gallon (3.785411784 L), the international table BTU (1055.05585 J) and the thermochemical calorie (4.184 J). Pick the one your source uses; they differ in the third digit.
Quick reference: common engineering conversions
| Unit | Equals |
|---|---|
| 1 ksi | 6.894757 MPa (N/mm²) |
| 1 psi | 6.894757 kPa |
| 1 bar | 14.50377 psi |
| 1 MPa (N/mm²) | 145.0377 psi |
| 1 atm | 101.325 kPa |
| 1 lbf·ft | 1.355818 N·m |
| 1 lbf·in | 0.1129848 N·m |
| 1 N·m | 0.7375621 lbf·ft |
| 1 kgf·m | 9.80665 N·m |
| 1 lbf | 4.448222 N |
| 1 kip (1000 lbf) | 4.448222 kN |
| 1 kgf | 9.80665 N |
| 1 N | 0.2248089 lbf |
| 1 in | 25.4 mm |
| 1 ft | 0.3048 m |
| 1 thou (mil) | 25.4 µm |
| 1 hp (mechanical, 550 ft·lbf/s) | 0.7456999 kW |
| 1 PS / CV (metric hp) | 0.7354987 kW |
| 1 lb | 0.4535924 kg |
| 1 slug | 14.5939 kg |
| 1 ft·lbf | 1.355818 J (N·m) |
| 1 kWh | 3.6 MJ |
| 1 lb/in³ | 27.6799 g/cm³ |
| 1 lb/ft³ | 16.01846 kg/m³ |
Worked example: a torque and a stress from a US drawing
A drawing calls for a fastener torque of 65 lbf·ft and a material yield of 36 ksi. In SI, 65 lbf·ft × 1.355818 = 88.13 N·m, and 36 ksi × 6.894757 = 248.2 MPa. A pressure of 3000 psi is 3000 × 0.00689476 = 20.68 MPa, or 206.8 bar. Enter the numbers above to check each one, then use them in the bolt torque or beam deflection calculators, which accept both unit systems.
Questions
How many MPa is 1 ksi?
1 ksi is 6.894757 MPa (6.894757 N/mm²). It follows from 1 lbf = 4.4482216 N and 1 in = 25.4 mm exactly. To go the other way, 1 MPa is 0.145038 ksi or 145.038 psi.
How do I convert N·m to lbf·ft?
Divide by 1.355818. For example 100 N·m is 73.76 lbf·ft. Going the other way, multiply lbf·ft by 1.355818 to get N·m.
Is N/mm² the same as MPa?
Yes. 1 N/mm² = 1 MPa = 1 000 000 Pa exactly, because 1 mm² is 10⁻⁶ m². The converter lists MPa (N/mm²) as one unit.
What is the difference between mechanical horsepower and metric horsepower?
Mechanical (imperial) horsepower is defined as 550 ft·lbf/s = 745.700 W. Metric horsepower (PS, CV, cheval vapeur) is 75 kgf·m/s = 735.499 W. They differ by about 1.4 percent, so check which one a catalogue uses.
How is the kilogram-force defined?
One kilogram-force is the force that standard gravity, 9.80665 m/s², exerts on a mass of 1 kg: 9.80665 N exactly. It is still found on older drawings and in some catalogues; the SI unit is the newton.
Does the converter round the factors?
No. Conversions use the exact legal definitions where they exist (1 in = 25.4 mm, 1 lb = 0.45359237 kg, standard gravity 9.80665 m/s²) and the best published values otherwise. Results are shown to 7 significant digits; use fewer in your design.
How do I convert a pressure in bar to psi?
Multiply by 14.5038. For example a 6 bar air supply is 87.02 psi, and a 3000 psi hydraulic system is 206.8 bar.
Engineering aid for guidance. Conversion factors are exact where an exact definition exists and rounded to 7 significant digits in the table; the pressure head units (inH₂O, mH₂O) assume water at 4 °C. Units named after a country (gallon, ton, BTU, calorie) have more than one definition; check which one your source means. Verify critical designs; you remain responsible for the design. Nothing you enter leaves your browser except through a share link you copy yourself.