Engineering unit converter

Vendor A quotes pressure in psi, vendor B in bar, and the P&ID is in kPa. The converter covers the units that actually appear in datasheets, loop drawings, and HMI faceplates: pressure (Pa, kPa, MPa, bar, mbar, psi, inH₂O, mmHg, atm), temperature (°C, °F, K), flow (L/min, m³/h, gpm, cfm), level/length (mm, cm, m, in, ft), and mass (kg, lb).

The conversions people get wrong

Gauge vs absolute. psi, bar, and kPa in process contexts are usually gauge (relative to atmosphere); add ~1.013 bar for absolute. Vacuum in inHg or mbar is already a differential — convert the magnitude, keep the sign convention.

Temperature intervals vs points. A 10 °C span is 18 °F of span, but 10 °C is 50 °F as a point. The converter handles points; for spans, multiply/divide by 1.8 only.

Flow and sizing. Rotameters and orifice plates are calibrated at specific conditions — converting gpm to m³/h is exact math, but the reading is only valid at the calibrated density. Note the conditions on the datasheet before trusting converted flow in a sizing calculation.

See also

• 4–20 mA loop scaling — the next step after the transmitter
• RTD and thermocouple — Shopfloor glossary