EngineerHub.orgDrawing No. EH–GE–012 // General Engineering
Unit Converter
Reviewed August 2026
Convert between SI and US customary units across the categories engineers hit most often. Pick a category, enter a value, and the result updates as you type.
Drawing No. EH–GE–012 // General Engineering
Reviewed August 2026
Convert between SI and US customary units across the categories engineers hit most often. Pick a category, enter a value, and the result updates as you type.
Linear unit conversion — multiply by a fixed factor between units.
Converting a pressure, and why the offset units are different.
Most engineering conversions are a single multiplication: 1 bar = 100 000 Pa, so 2.5 bar becomes 250 000 Pa, and 150 psi × 6894.76 = 1.034 MPa.
valueSI = value × factor (temperature: value × factor + offset)
Temperature is the exception that catches people out. °C to °F is not a single factor: 20 °C × 1.8 + 32 = 68 °F. A temperature difference of 20 K, however, is 36 °F-degrees — the offset applies to points on the scale, never to intervals. The same distinction applies to gauge and absolute pressure, where the offset is atmospheric pressure.
Points that come up most often with this calculation.
Because the offset belongs to the scale, not to the interval. Convert a point with °F = °C × 1.8 + 32, but convert a difference with ΔF = ΔC × 1.8. Mixing the two is one of the most common unit errors in engineering.
Gauge pressure is measured relative to the surrounding atmosphere, absolute from a vacuum. They differ by about 101.3 kPa at sea level. Thermodynamic property tables almost always expect absolute.
Whichever the governing standard uses. Convert once at the start, calculate throughout in that system, and convert back only for presentation — converting mid-calculation is where rounding errors and mistakes creep in.
The factors used are the exact defined values where one exists — 1 in = 25.4 mm exactly, 1 lbf = 4.4482216152605 N exactly. Where a unit is defined by measurement rather than definition, the CODATA recommended value is used.
Include the inputs and assumptions used.