Conversion of physical quantities in SI measurement units

Conversion-of-physical-quantities-in-SI-measurement-units

The international measurement system SI (System International) is worldwide accepted at the present time. Metric units are widely used both in science and in everyday life almost in all states. The exceptions are the USA, Liberia and Myanmar.

However, quite often, when using foreign literature (books, reference books, booklets, journals), an engineer has to face with non-systemic measurement units such as foot, Fahrenheit degrees, pound and others. For example, in booklets, presented by the Manufacturer of Bitzer or Cubigel refrigeration equipment, the refrigeration capacity of reciprocating and screw compressors is given in Btu/h. When designing the refrigeration units, it will be no trouble for an experienced specialist to convert these quantities into SI measurement units, even not using a calculator, but this task can somewhat confuse a beginning designer and can lead to making mistakes at maintenance of cooling system.

In global network Internet, if desired, there can be found many services enabling to convert physical quantities from one measurement units to other ones in online mode. But as per Murphy’s law (the second name – Sod’s law :) ), one always needs to convert the quantity values in metric system at a most unsuitable moment, for example, when there is no access to Internet.

This article is meant for the following:

  1. to fill a gap in beginning engineer’s knowledge;
  2. to help in speeding up the process of conversion of non-systemic physical quantities in SI system measurement units;
  3. to broaden knowledge of any reader of this blog.

So let us clear up! :)

Value

Measurement

unit in SI

Dependences
Length

m

(metre)

1 Å (Angstrom) = 10-10 m
1 inch (abbr. in) = 0.0254 m
1 foot (fееt, abbr. ft) = 12 inches = 0.3048 m
1 yard (abbr. yd) = 3 feet = 0.9144 m
Area

m2

(square metre)

1 in2 = 0.0006452 m2
1 ft2 = 0.0929 m2
1 yd2 = 0.8361 m2
Volume

m3

(cubic metre)

1 l (litre) = 0.001 m3
1 in3 = 0.00001639 m3
1 ft3 = 0.02832 m3 = 28.32 l
1 yd3 = 0.7646 m3
1 gallon (abbr. gal) = 0.0037852 m3 = 3.7852 l
Mass

kg

(kilogram)

1 ounce (ounces, abbr. oz) = 0.02835 kg
1 pound (abbr. lb) = 16 ounces = 0.4536 kg
1 centner = 100 kg
1 t (ton) = 1000 kg
1 net ton [short ton] = 2000 pounds = 907.185 kg
1 gross ton [long ton] = 2240 pounds = 1016.05 kg
Time

s

(second)

1 hour = 3600 s
1 day = 86400 s
1 year (not a leap year) = 31536000 s
Plane angle

rad

(radian)

1° (degree) = π/180 rad
1′ (minute) = π/10800 rad
1” (second) = π/648000 rad
1 rev. (revolution) = 2·π rad = 6.2832 rad
Frequency

Hz

(Hertz)

1 Hz = 1 s-1
1 rev/s = 1 Hz
1 rev/min = 0.0167 Hz
Linear velocity m/s 1 ft/s = 0.3048 m/s
1 mile/h = 0.447 m/s
1 km/h = 0.2778 m/s
Angular velocity rad /s 1 rev/min = π/30 rad/s
1 rev/s = 2·π rad/s
Linear acceleration m/s2 1 in/s2 = 0.0254 m/s2
1 ft/s2 = 0.3048 m/s2
Specific volume m3/kg 1 ft3/lb = 0.06243 m3/kg
Density kg/m3 1 oz/ft3 = 1.0 kg/m3
1 lb/ft3 = 16.0185 kg/m3
1 lb/in3 = 27680.37 kg/m3
Force

N

(Newton)

1 dyne = 10-5 N
1 lbf = 4.45 N
1 kgf (kilogram-force) = 9.80665 N
1 sthene = 103 N
Pressure

Pa

(Pascal)

1 kgf/cm2 = 1 at (atmosphere) = 98066.5 Pa = 736.5 mm m. c.
1 bar = 105 Pa = 1.0197 kgf/cm2
1 mm w. c. = 9.80665 Pa
1 mm m. c. = 133.32 Pa
1 lbf/in2 = 6894.76 Pa
1 lbf/ft2 = 47.88 Pa
Temperature

К

(Kelvin)

Kelvin scale: T, K = t, °C + 273.15
Fahrenheit scale: t, °F = (9/5)·t, °C + 32
Celsius scale: t, °C = (5/9)·(t, °F – 32)
Reaumur scale: t, °R = 0.8·t, °C
Surface tension N/m 1 kgf/m = 9.81 N·m
Mass flow rate kg/s 1 lb/s = 0.4536 kg/s
1 lb/h= 0.000126 kg/s
Volume flow rate m3/s 1 l/min = 0.00001667 m3/s
1 ft3/s = 0.02832 m3/s
1 in3/s = 0.00001639 m3/s
Dynamic viscosity coefficient Pa·s 1 kgf·s/m2 = 9.81 Pa·s
1 P (Poise) = 0.1 Pa·s
1 lbf·s/ft2 = 47.88 Pa·s
Kinematic viscosity coefficient m2/s 1 St (Stokes) = 0.0001 m2/s
1 ft2/s = 0.0929 m2/s
1 ft2/h = 334.45 m2/s
Diffusion coefficient m2/s 1 ft2/s = 0.0929 m2/s
Viscosity coefficient kg/(m·s) 1 lb/(ft·s) = 1.488 kg/(m·s)

Work, Energy,

Quantity of heat

J

(Joule)

1 erg = 10-7 J
1 lbf·in = 0.113 J
1 lbf·ft = 1.3558 J
1 cal (calorie) = 4.1868 J
1 kgf·m = 9.80665 J
1 kW·h = 860 kcal = 3603.4 kJ
1 Btu (British thermal unit) = 1055.06 J
1 pcu (pound centigrade unit) = 1899.11 J

Power,

Heat flux,

Refrigeration capacity

W

(Watt)

1 h. p. = 736 W
1 kcal/h = 1.163 W
1 lbf·ft/с = 1.356 W

Heat flux density

(Heat stress,

Specific heat load)

W/m2 1 kcal /(м2·h) .1.163 W/m2
1 Btu/(ft2·h) = 3.155 W/m2
1 pcu/(ft2·h) = 5.678 W/m2

Specific enthalpy, Specific heat

of phase transition

J/kg 1 kcal /kg = 4.1868 kJ/kg
1 Btu/lb = 2325.97 J/kg

Specific mass heat capacity,

Specific entropy

J/(kg·К) 1 kcal/(kg·ºC) = 4.1868 kJ/(kg·K)
1 erg/(g·ºC) = 0.0001 J/(kg·К)
1 Btu/(lb·ºF) = 4.1868 kJ/(kg·K)
Heat conduction coefficient W/(m·K) 1 kcal/(m·h·ºC) = 1.163 W/(m·K)
1 Btu/(ft·h·ºF) = 0.962 W/(m·K)
1 Btu/(in·h·ºF) = 11.538 W/(m·K)
Heat transfer coefficient W/(m2·K) 1 kcal/(m2·h·ºC) = 1.163 W/(m2·K)
1 Btu/(ft2·h·ºF) = 3.154 W/(m2·K)
1 pcu/(ft2·h·ºF) = 5.678 W/(m2·K)
Radiation coefficient W/(m2·K4) 1 kcal/(м2·h·K4) = 1.163 W/(m2·K4)

When writing this article it came to my mind to dedicate one of the next articles to the usage of prefixes (“kilo”, “mega”, “milli”, “micro”) for physical quantities.

If you find any mistakes, please don’t hesitate and point them out!

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21 thoughts on “Conversion of physical quantities in SI measurement units

  1. Помню, когда еще училась в школе на физмате, то приходилось выписывала отдельно себе на листочек все эти величины, чтобы всегда были под рукой. А потом со временем они просто запомнились, и теперь перевести любую величину в СИ не составляет огромного труда.

    • по нашему скромному мнению, понятие “Инженер” очень широкое. может быть Инженер по котлам, инженер по турбинам, инженер по ДВС, инженер по конструкциям и т.д.
      Мы всего лишь занимаем область холодильного оборудования ;)

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