Unit Converter
Converts a value between the common SI and US customary units for 30 engineering quantities: geometry (length, area, volume, second moment of area), force, stress and pressure, torque, mass and density, motion, time and frequency, fluid flow and viscosity, temperature and heat transfer, energy and power, and electrical units. Every equivalent unit is listed at once, so one entry answers several conversions.
How the conversion works
Each quantity has one reference unit (millimetres for length, megapascals for stress, newtons for force). The value is multiplied by its unit’s factor to reach the reference unit, then divided by the factor of the unit wanted. The factors follow the exact definitions in NIST SP 811 [1]: 1 in = 25.4 mm, 1 lb = 0.45359237 kg and standard gravity gn = 9.80665 m/s², so 1 lbf = 4.4482216152605 N; 1 yd = 0.9144 m and 1 mi = 1609.344 m. A day is 86 400 s; a year is the Julian year of 365.25 days, and a month one twelfth of it, 30.4375 days. Calendar months and years vary in length, so a conversion through them is an average.
Inputs
- Search (optional): type a quantity or a unit, such as “torque” or “psi”, to narrow the Physical Quantity list. Typing a unit symbol exactly also selects it as the From unit.
- Value, From Unit and To Unit: the number to convert, the unit it is in, and the unit you want. The results update as you type.
- Significant Figures: how many figures each result is rounded to, from 1 to 15. A result marked “(rounded)” has more digits than are shown. Choose no more figures than the value you entered is known to; a gauge reading of 3,000 psi rarely justifies more than three or four.
When to use which temperature
Use Temperature (Absolute) for a reading on a thermometer, where the scales are offset: °F = °C × 9/5 + 32, so 10 °C is 50 °F. Use Temperature Difference for a rise, a drop or a range, where the offset cancels: a 10 °C rise is an 18 °F rise. Choosing the wrong one is the most common unit-conversion mistake in heat-transfer work.
Worked example
Convert a hydraulic pressure of 3,000 psi to MPa. One psi is one pound-force per square inch:
1 psi = 4.4482216 N ÷ (25.4 mm)² = 4.4482216 N ÷ 645.16 mm² = 0.0068947573 N/mm² = 0.0068947573 MPa
3,000 psi × 0.0068947573 MPa/psi = 20.684272 MPa ≈ 20.7 MPa (3 significant figures)
Enter 3000, From psi, To MPa, and the Solution shows 20.6843 MPa at the default 6 figures, along with the same pressure in Pa, kPa, GPa, bar, psf and ksi.