Unit Converter for Engineers
Convert 327 engineering units across 44 categories — pressure, flow, viscosity, torque, thermal conductivity, section modulus — in SI, metric and US/Imperial.
When to use this calculator
Use it whenever a datasheet, vendor quote, or standard arrives in the wrong unit system: a pump curve in GPM and feet of head against a spec in m³/h and bar, a US mill certificate in ksi next to an EN allowable in MPa, a viscosity in centistokes when the correlation wants m²/s. It covers the engineering quantities that general-purpose converters skip — second moment of area, section modulus, moment of inertia, specific volume, mass flux density, molar flow, heat transfer coefficient, thermal expansion coefficient, and permeability in darcy/millidarcy.
Required inputs
- Unit category — 44 available, grouped as Common, Engineering, Fluids, and Heat & Energy
- Source value
- Source unit and target unit (searchable within the category)
- Output precision — auto, 2, 4, or 6 decimals, or scientific notation
Expected outputs
- Converted value at the selected precision
- Conversion factor line (1 source unit = N target units)
- Unit metadata — full name, symbol, measurement system, and the category base unit
- Copy-to-clipboard result
Formula overview
SI, metric, metric-gravitational (kgf/cm², kgf·s/m²), US/Imperial, and scientific units sit side by side in each category — pressure alone carries 19 units including bar, psi, ksi, MPa, kgf/cm², atm, Torr, mmHg, inHg, and head units (mH₂O, inH₂O, ftH₂O). Each unit is tagged with its system, and rarely used ones are marked Specialized.
Every category converts through one SI base unit, using one of four methods:
linear base = value × factor out = base ÷ factor
affine base = value × factor + off out = (base − off) ÷ factor
reciprocal base = constant ÷ value out = constant ÷ base
radix parse in source base, format in target base
linear covers pressure, flow, torque, viscosity and most of the catalogue.
affine is used only for absolute temperature (K, °C, °F, °R).
reciprocal handles inverse quantities such as fuel economy (km/L ↔ L/100 km).
radix converts integers between decimal, binary, octal and hexadecimal.Worked example
1) Linear — pressure, 10 bar → psi
base = 10 × 100 000 = 1 000 000 Pa
out = 1 000 000 ÷ 6894.757293 = 145.04 psi
2) Affine — temperature, 100 °C → °F
base = 100 × 1 + 273.15 = 373.15 K
out = (373.15 − 255.372222) ÷ 0.555556 = 212.00 °F
3) Reciprocal — fuel economy, 12 km/L → L/100 km
base = 100 ÷ 12 = 8.33 L/100 km
4) Flow — 50 m³/h → US GPM
base = 50 × 0.000277778 = 0.013889 m³/s
out = 0.013889 ÷ 0.0000630902 = 220.10 gpmCommon mistakes
- Confusing gauge with absolute pressure. The converter scales magnitudes only — it has no gauge/absolute datum switch, so add or subtract atmospheric pressure yourself (bara = barg + 1.01325).
- Converting a temperature difference in the Temperature category. An 80 °C rise is not 176 °F — use the separate Temperature Interval category, where 1 °C = 1 K and 1 °F = 0.555556 K.
- Mixing US and Imperial gallons. US gpm and UK gpm differ by about 20% (0.0000630902 vs 0.0000757682 m³/s), and the same trap applies to mpg (US) vs mpg (UK).
- Treating kgf/cm² as exactly 1 bar. It is 0.980665 bar — a 2% error that matters on a hydrotest or a relief-valve set point.
- Reading kgf/cm² or mmH₂O off an old gauge and entering it as SI without converting, or using mechanical horsepower (745.70 W) where the datasheet meant metric PS (735.50 W).
FAQ
Learn
Related articles
Pressure Vessel Design & Calculation: คู่มือออกแบบตาม ASME Sec VIII Div 1
คู่มือออกแบบ pressure vessel และความหนา shell/head ตาม ASME Sec VIII Div 1 พร้อมสูตรและตัวอย่างคำนวณ
NPSHa vs NPSHr ต่างกันอย่างไร
เข้าใจความแตกต่างระหว่าง NPSH available และ NPSH required เพื่อป้องกัน cavitation ในปั๊ม