Units of Conversions Used in Mechanical Engineering

Below are the units of conversions that are used in mechanical engineering. Our further articles will be using those conversion units. This is posted for the information so that while going through related articles you should not face any problem in understanding.

The previous article on the symbols, its meaning, the SI units and its values is associated with the topic and add value to our forth coming articles. If you have not gone through the previous one, please read that here.

Base Units
Type	SI Unit	USCS unit	Other conversions
Length	meter (m)	1 foot (ft) = 3.281 m	1 m = 100 centimeters (cm)        = 1000 millimeters (mm)        = 39.37 inches (in) 1 kilometer (km) = 1000 m 1 mile (mi) = 5280 ft
Mass	kilogram (kg)	2.205 pounds mass (lbm)= 1 kg	1000 grams (g) = 1 kg 1 slug = 32.174 lbm
Time	second (s)	s	1 minute (min) = 60 s 1 hour (hr) = 60 min
Charge	Coulomb (coul)	coul	1 coul = charge on 6.241506 x 10 18 electrons
Derived Units
Type	SI Unit	USCS unit	Other conversions
Area (length 2 )	m2	10.76 ft 2 = 1 m 2	1 acre = 43,560 ft 2 640 acres = 1 mi 2 1 hectare = 10,000 m 2 = 2.471
Volume (length 3 )	m3	35.32 ft 2 = 1 m 3	1 ft 3 = 7.48 gallons (gal) = 28,317 cm 3 1 m 3 = 264.2 gal 1 liter = 0.001 m 3 = 1000 cm 3 = 61.02 in 3
Velocity (length/time)	m/s	3.281 ft/s = 1 m/s	60 mi/hr = 88 ft/s
Acceleration (length/time 2 )	m/s 2	3.281 ft/s 2 = 1 m/s 2	1 g (standard earth gravity) = 9.806 m/s 2 = 32.174 ft/s 2
Force = mass×length time 2	1 Newton (N) = 1 kg m/s 2	1 pound force (lbf) = 4.448 N	1 dyne = 1 g cm/s 2 = 10 -5 N
Energy = mass×length 2 time 2	1 Joule (J) = 1 kg m 2 /s 2	1 foot-pound (ft lbf) = 0.7376 J	1 British Thermal Unit (BTU) = 1055 J = 778 ft lbf 1 calorie (cal) = 4.184 J 1 diet calorie = 1000 cal 1 erg = 1 g cm 2 /s 2 = 10 -7 J
Power = mass×length 2 time 3	1 Watt (W) = 1 kg m 2 /s 2	1 horsepower (hp) = 746 W	1 hp = 550 ft lbf/s
Pressure = force/length 2	1 Pascal (Pa) = 1 N/m 2 = 1 kg/m s 2	1 lbf/in 2 = 6899 Pa	1 standard atmosphere (atm) = 101325 Pa = 14.696 lbf/in 2 1 bar = 10 5 Pa
Temperature	Kelvin (K)	1.8 Rankine (R) = 1 K	See notes below
Heat capacity = Energy mass × temperature	1 J /kg K = 1 J/kg˚C	1 BTU/lbm˚F = 1 BTU/lbmR = 1 J/kg˚C	(Note: that’s not a misprint, the SI to USCS conversion factor is exactly 1 in this case)
Current = charge/time	1 Ampere (A or amp) = 1 coul/s	n/a	1 milliamp (mA) = 0.001 A
Voltage = energy/charge	1 Volt (V) = 1 J/coul	n/a	n/a
Capacitance = coul/Volt	1 Farad (f) = 1 coul/Volt = 1 coul 2 /J	n/a	1 microfarad (µf) = 10 -6 f 1 picofarad (pf) = 10 -12 f
Inductance = Volt / (amp/s)	1 Henry (H) = 1 J s 2 /coul 2	n/a	1 millihenry (mH) = 0.001 H
Resistance = Volt/amp	1 Ohm (Ω) = 1 Volt/amp = 1 J s/coul 2	n/a	n/a

Temperature Conversion Formulae:

Kelvins (K, not ˚K) is the absolute temperature scale in SI units.

Rankines (R, not ˚R) is the absolute temperature scale in USCS units.

T (in units of ˚F) = T (in units of R) - 459.67

T (in units of ˚C) = T (in units of K) - 273.15

T (in units of ˚C) = [T (in units of ˚F) – 32]/1.8

T (in units of ˚F) = 1.8[T (in units of ˚C)] + 32

Revolution Conversion Formulae: 

1 revolution = 2π radians = 360 degrees