Convert SI and engineering units within a selected physical quantity. Check the dimension, inspect the conversion factors and SI intermediate value, and distinguish temperature readings from temperature differences.
02 Read the converted value
Pressure
bar
Enter a value to begin.
- SI intermediate
- Dimension
Results display up to 10 significant digits. Factors and arithmetic use full stored precision.
03 Trace the conversion
Conversion method and dimension checks
For a multiplicative conversion, let a be the SI factor of the source unit and b the SI factor of the destination unit. Then SI value = x × a and converted value = x × (a/b). The engine checks that both units belong to the selected quantity before converting.
Dimensions use M for mass, L for length, T for time, and Θ for temperature. For example, pressure has dimension M·L⁻¹·T⁻². Energy and power have different time exponents, so kWh cannot be converted directly to kW. Dynamic and kinematic viscosity also have different dimensions.
The converter covers length, area, volume, mass, time, absolute temperature, temperature difference, pressure, energy, power, speed, mass flow, volumetric flow, density, dynamic viscosity, kinematic viscosity, mass-specific heat capacity, heat-transfer coefficient, and thermal conductivity.
Temperature readings and differences
Choose Absolute temperature for a scale reading and Temperature difference for an increase or decrease. They share dimension Θ but have different conversion rules; matching dimensions alone does not establish the intended meaning.
| Quantity | Conversion to kelvin | Example |
|---|---|---|
| Absolute Celsius reading | T(K) = T(°C) + 273.15 | 0 °C = 273.15 K |
| Absolute Fahrenheit reading | T(K) = [T(°F) − 32] × 5/9 + 273.15 | 32 °F = 0 °C |
| Absolute Rankine reading | T(K) = T(°R) × 5/9 | 0 °R = 0 K |
| Temperature difference | ΔT(K) = ΔT(°C) = ΔT(°F) × 5/9 | 18 °F difference = 10 K difference |
Absolute temperatures below 0 K, −273.15 °C, or −459.67 °F are rejected. Negative temperature differences are allowed. Temperature terms in heat capacity, heat-transfer coefficients, and thermal conductivity are differences and use scale factors without offsets.
Basis and limitations
- Pressure reference stays unchanged. Gauge values remain gauge and absolute values remain absolute. A gauge-to-absolute calculation needs a reference pressure and is not performed here. The atm unit is 101325 Pa; it does not set the local atmospheric pressure.
- Property-dependent changes are separate calculations. Mass flow to volumetric flow requires density; mass flow to molar flow requires molar mass; dynamic to kinematic viscosity requires density. None is an interchangeable unit pair.
- Operating conditions stay unchanged. Volumetric unit conversion does not convert normal/standard gas volumes into actual volumes at another temperature or pressure.
- Definitions are explicit. US gal means U.S. liquid gallon, Imp gal means Imperial gallon, Btu_IT means International Table Btu, kcal_th means thermochemical kilocalorie, and hp means mechanical horsepower. International foot/inch and avoirdupois mass units are used.
- Other than the absolute-temperature limit, values are converted algebraically, including signed values. Converting a negative pressure does not establish whether it is a physically valid absolute pressure.
- Arithmetic uses browser double precision. Results display up to 10 significant digits; intermediate factors display up to 12. A nonfinite result or nonzero result that underflows to zero is rejected. The report identifies an unrepresentable SI intermediate separately when the requested conversion is still finite.
Worked examples
Pressure: convert 101.325 kPa to bar. The source factor is 1000 Pa/kPa; the destination factor is 100000 Pa/bar. Therefore xSI = 101325 Pa and y = 101.325 × 1000/100000 = 1.01325 bar, with the original pressure reference retained.
Temperature: 32 °F as an absolute reading converts to 0 °C. An interval of 18 °F converts to a 10 K interval. Volume: 1 US gal converts to 3.785411784 L, while 1 Imp gal converts to 4.54609 L. Each quantity has a “Load example” case in the converter.
Sources and calculation version
NIST SP 811, Appendix B.9: conversion factors by quantity supplies the reference unit definitions and factors. Compound factors are calculated from those definitions, including 1 ft = 0.3048 m, 1 lbm = 0.45359237 kg, 1 Btu_IT = 1055.05585262 J, and 1 cal_th = 4.184 J.
Changelog: engine and factor registry 1.0.0 introduce the selected engineering quantities, semantic unit checks, separate absolute/interval temperature handling, factor and SI tracing, examples, swapping, and range validation. No material-property or operating-condition dataset is used. Engineering review status: independent review pending.