Formula
converted value = value × (factor of the original unit ÷ factor of the target unit) °F = °C × 9/5 + 32 K = °C + 273.15
Each unit has one factor to a base unit (m for length, m² for area, kg for mass, L for volume, kPa for pressure, kJ for energy, kW for power). The value is converted to the base unit and then divided by the target unit's factor. Temperature scales have different zero points, so they use the equations above instead of a single factor.
The factors are built from exact definitions: 1 ft = 0.3048 m, 1 lb = 0.45359237 kg, standard gravity 9.80665 m/s², US gallon = 231 in³, imperial gallon = 4.54609 L and International Table calorie = 4.1868 J. For example, 1 psi = 1 lbf/in² = 0.45359237 × 9.80665 ÷ 0.0254² ≈ 6,894.757 Pa; metric horsepower (PS) = 75 kgf·m/s = 735.49875 W; mechanical horsepower = 550 ft·lbf/s ≈ 745.69987 W. The International Table Btu follows from 1 Btu/(lb·°F) = 1 cal/(g·°C): 4.1868 × 453.59237 × 5/9 ≈ 1,055.056 J.
Traditional Korean units
Korea dropped these units from legal use in 1961, and using them in trade or advertising has been subject to fines since July 2007. They are still common in everyday speech, especially pyeong for floor area, so the converter includes them.
| Unit | Value | Notes |
|---|---|---|
| ja | 10/33 m ≈ 0.303 m | Length; one side of a pyeong is 6 ja |
| pyeong | 400/121 m² ≈ 3.3058 m² | 6 ja × 6 ja = 36 square ja |
| don | 3.75 g | Used for gold and silver |
| nyang | 37.5 g | 10 don |
| geun (meat) | 600 g | Butcher's geun |
| geun (produce) | 375 g | 100 don; used for some fruit and vegetables |
| gwan | 3.75 kg | 1,000 don |
| hop · doe · mal | 0.18039 · 1.8039 · 18.039 L | Grain volume; 10 hop = 1 doe, 10 doe = 1 mal |
Choosing inputs
- Pressure: gauge pressure (relative to the atmosphere) and absolute pressure differ by about 101.325 kPa even in the same unit. This converter changes the unit only, not the reference.
- Power: metric horsepower (PS, CV) appears on many European and Japanese nameplates, mechanical horsepower (hp) on US ones. They differ by about 1.4 %.
- Gallons: US products use the US gallon and older UK data the imperial gallon. They differ by about 20 %, so check where the figure came from.
Worked example
A compressor gauge reads 100 psi. What is that in kPa and bar?
- 1 psi ≈ 6.894757 kPa
- 100 × 6.894757 ≈ 689.48 kPa ≈ 6.89 bar
The calculator opens with these values.
Limitations
- Results are rounded to about seven significant figures on screen. The factors themselves are exact definitions.
- Calories use the International Table calorie (4.1868 J). Sources using the thermochemical calorie (4.184 J) differ by about 0.07 %.
- Units with field-specific definitions, such as food calories or the ton of refrigeration, are not included.
References
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI), Appendix B, Conversion factors
- Wikipedia, "Korean units of measurement" and "Pyeong" (pyeong = 400/121 m² ≈ 3.3058 m²; geun 600 g and 375 g)
- Wikipedia, "Gallon" (US gallon = 231 in³ = 3.785411784 L; imperial gallon = 4.54609 L)
- KnowledgeDoor, Units and Constants Handbook: horsepower (745.69987158 W) and metric horsepower (735.49875 W)