Engineering Unit Converter
Convert the physical quantities common in mechanical engineering between metric and US customary units: power, torque, pressure, force, length, mass, speed and temperature. Each quantity has its own card – enter a value, pick the source unit, and every target unit appears instantly.
Convert units
Power
Torque
Pressure
Force
Length
Mass
Speed
Temperature
All cards convert factor-based through an SI base unit; temperature uses an affine conversion with a zero-point offset and applies to absolute values only, not to temperature differences. The display rounds to six significant figures.
Formulas and fundamentals
Factor-based quantities are converted through a common SI base unit: the input value is scaled into the base by the source unit's factor and then divided by the target unit's factor. For power the base is the watt, with 1 kW = 1000 W, 1 PS = 735.49875 W (metric horsepower, 75 kp·m/s) and 1 hp = 745.699872 W (mechanical horsepower). For pressure the base is the pascal, with 1 bar = 100,000 Pa, 1 MPa = 1,000,000 Pa and 1 psi = 6894.757 Pa.
Force, torque, length and mass follow the same scheme. Force in newtons: 1 kp = 9.80665 N (kilopond, the old technical unit of force), 1 lbf = 4.448222 N. Torque in newton metres: 1 kp·m = 9.80665 Nm, 1 lb·ft = 1.355818 Nm. Length in metres: 1 in = 25.4 mm, 1 ft = 304.8 mm. Mass in kilograms: 1 lb = 0.45359237 kg, 1 t = 1000 kg. The constant 9.80665 m/s² is the standard gravitational acceleration that defines all kilopond units (kp, kp·m).
Temperature is the only quantity with an affine conversion because the scales have different zero points: Celsius maps to the kelvin base via T[K] = T[°C] + 273.15, Fahrenheit via T[K] = (T[°F] − 32)·5/9 + 273.15. The reverse conversion inverts the relation. Hence 0 °C = 273.15 K = 32 °F, and a temperature difference of 1 K equals 1 °C but 1.8 °F.
Worked example
A motor delivers 100 kW. In the Power card you enter 100 and select kW as the source unit. The converter immediately shows 135.96 PS and 134.10 hp – the difference between metric PS and mechanical horsepower is about 1.4 percent and is often overlooked in practice.
A hydraulic pressure of 1 bar equals 14.50 psi, 100,000 Pa and 0.1 MPa. A tightening torque of 100 Nm equals 73.76 lb·ft and 10.20 kp·m. A length of 1000 mm is exactly 39.37 in and 3.281 ft.
For temperature the converter shows 293.15 K and 68 °F for 20 °C. Important: these cards convert absolute values, not temperature differences. A difference of 10 K does equal 10 °C, but 10 °C is not 50 °F – here the factor 1.8 applies (i.e. 18 °F).
Frequently asked questions
What is the difference between PS and hp?
PS is metric horsepower (1 PS = 735.49875 W = 75 kp·m/s), hp is US/UK mechanical horsepower (1 hp = 745.699872 W). One hp is about 1.4 percent stronger than one PS. Vehicle and motor ratings from English-speaking markets almost always mean hp.
What does kp mean and why does 9.80665 appear?
kp stands for kilopond, the old technical unit of force: 1 kp is the weight force of 1 kg under the standard gravitational acceleration g = 9.80665 m/s². Hence 1 kp = 9.80665 N and 1 kp·m = 9.80665 Nm. Modern calculations use newtons consistently, but kp still appears on older drawings and datasheets.
Does the tool convert temperature differences or absolute values?
Absolute values. The temperature card uses the full scale offset (0 °C = 273.15 K = 32 °F). Temperature differences follow different rules: 1 K = 1 °C = 1.8 °F, with no offset. Use the card only for individual temperature readings, not for spans.
Why is 1 bar not exactly 1 kg/cm²?
1 bar = 100,000 Pa is a decimal unit, whereas the technical atmosphere at (kp/cm²) depends on gravity: 1 at = 98,066.5 Pa. The difference is about 2 percent. This converter works with bar, Pa, kPa, MPa and psi; for rough estimates 1 bar ≈ 1 kg/cm² is nonetheless often used.
How accurate are the conversion factors?
The factors match the defined or generally accepted values (e.g. 1 in = 25.4 mm exactly, 1 lb = 0.45359237 kg exactly, 1 psi = 6894.757 Pa). The display rounds to six significant figures. For billing or certification purposes the applicable standard values govern.
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