Same-quantity conversions
For any two units that measure the same physical quantity, the conversion is a single fixed factor derived from SI definitions or an accepted engineering constant. The factor does not depend on the value being converted, the user, or the session — multiplying by it gives the same result every time.
Examples include pressure (Pa, bar, psi), length (m, ft, in), mass (kg, lb), power (W, hp), volume (m³, L, gal) and similar categories where the relationship is purely multiplicative.
Temperature is handled separately
Temperature conversions between Celsius, Fahrenheit, Kelvin and Rankine involve offsets, not just multiplication. A simple factor cannot map 0 °C to 32 °F, and a constant scale cannot map Kelvin to Celsius. These conversions are implemented as explicit affine formulas so the offset is always applied correctly.
Non-deterministic conversions are excluded by default
Several common engineering conversions are not deterministic on their own — they require extra physical inputs that depend on the fluid, the process or the reference conditions. ProcessConvert deliberately avoids these unless the required inputs are explicit:
- Dynamic viscosity ↔ kinematic viscosity requires the fluid's density.
- Mass flow ↔ volumetric flow requires the fluid's density at the relevant conditions.
- ppm ↔ mg/L requires solution density, and often the solute's molecular weight.
- Normal or standard gas flow requires explicit reference temperature and pressure conditions.
Treating these as one-line conversions is a common source of error. Where they appear in ProcessConvert, they are scoped to defined inputs rather than assumed defaults.
Precision policy
- Displayed values are rounded for readability. The rounding is for the screen, not for the calculation.
- Conversion factors are stored deterministically in the data layer with more digits than are shown on the page.
- For the majority of conversions, the stored factor is more precise than typical process instrumentation, so display rounding is not the limiting source of error in a real measurement.
- For regulated, contractual or trade-specific work, users should cross-check against the relevant project, regulatory or industry standard.
Reference standards
Conversion factors are sourced from, or consistent with:
- SI definitions as published in the BIPM SI Brochure.
- NIST guidance on units, conversion factors and the use of the SI.
- ISO 80000 quantities and units, where relevant.
- Accepted engineering constants, such as standard gravity g₀ = 9.80665 m/s², where a conversion depends on one.
Report an error
If you spot a factor, label, symbol or formula that looks wrong, please tell us. Concrete reports — “the factor on page X shows Y, but it should be Z because…” — are especially helpful.