Key Unit Conversion Factors to Memorize

 Length
	1 in = 2.54 cm		(Exact)
	1 ft = 12 in		(Exact)
	1 yd = 3 ft		(Exact)
	1 mi = 5,280 ft		(Exact)

 Area
	1 acre = 4,840 yd2	(Exact)

 Volume
	1 cc = 1 cm3 = 1 mL	(Definition)
	1 mL = 20 drop (metric)	(Exact)
	1 gal = 231 in3	(Exact)
	1 gal = 4 qt		(Exact)
	1 qt = 2 pint		(Exact)
	1 pint = 2 cup 		(Exact)
	1 gal = 128 floz	(Exact)
	1 floz = 2 tbsp		(Exact)
	3 tsp = 1 tbsp		(Exact)

 Time
 	1 s = the duration of 9,192,631,770 periods of the radiation corresponding to the
	transition between the two hyperfine levels of the ground state of the cesium-133 atom.

	min = 60 s (Exact)
	h = 60 min (Exact)
	d = 24 h (Exact)
	yr = y = 365 d
	a = 365.25 d (Julian year - astronomy)

 Mass
	1 lbm = 453.6 gm
	16 oz = 1 lbm		(Exact)
	1 slug = 1 lbf-s2/ft	(Definition)
	1 lbf-s2/in = 175.1 kg

 Force
	1 lbf == 1 lbm on earth	(Definition)
	1 N = 1 kg-m/s2	(Definition)
	1 dyn = 1 gm-cm/s2 (Definition)
	1 N = 105 dyn  (1 dyn = 10 µN)
	1 lbf = 4.448 N
	1 ton = 2,000 lbf	(Exact)
	1 kip = 1,000 lbf	(Exact)

 Pressure
	1 Pa = 1 N/m2		(Definition)
	1 atm = 101,325 Pa	(Exact)
	1 bar = 100,000 Pa	(Definition)
	1 atm = 760 Torr	(Exact)
	1 Torr = 1 mmHg
	1 psi = 1 lbf/in2	(Definition)
	1 ksi = 1,000 psi	(Definition)
	1 atm = 14.7 psi

 Work-Energy
	1 J = 1 N-m		(Definition)
	1 erg = 1 dyn-cm	(Definition)
	1 J = 8.8507 in-lbf

 Power
	1 W = 1 J/s		(Definition)
	1 hp = 550 ft-lbf/s	(Exact)

 Temperature
 	1°R = 5/9 K             (Exact) (1 K is 1.8 times larger than 1 °R)
	[°F] = 9/5[°C] + 32     (Exact)
	[K] = [°C] + 273.15     (Exact)
	[R] = [°F] + 459.67     (Exact)

 Physical Constants
	1g = 386.1 in/s2
	1g = 9.81 m/s2

 Pound-force Conversion (gcF = ma)
	gc = 32.174 lbm-ft/(lbf-s2)

SI Unit Prefixes

	y	yocto	10-24
	z	zepto	10-21
	a	atto	10-18
	f	femto	10-15
	p	pico	10-12
	n	nano	10-9
	µ	micro	10-6
	m	milli	10-3
	c	centi	10-2
	d	deci	10-1
	da	deka	101
	h	hecto	102
	k	kilo	103
	M	mega	106
	G	giga	109
	T	tera	1012
	P	peta	1015
	E	exa 	1018
	Z	zetta 	1021
	Y	yotta 	1024

Exrta Information (not required to memorize)

Amount of Subtance

Definition of mole: The mole is a unit of measure to express the number of elementary entities of a chemical substance. One mole of entities is equal to the number of atoms in 12 grams of the carbon-12 (12C) isotope. This corresponds to the Avagadro constant of 6.022 141 79(30)×1023. 

1 mol = 6.022 141 79(30)×1023 N (SI base unit)
1 lbmol = lb-mol = 453.592 37 mol (12 lb of 12C)

NA = 6.022×1023 mol-1
NA = 2.731 597×1026 lbmol-1

Molar Mass

The mass, in grams, of a mole of a substance is called the molar mass. The units are M(X) = (g X / mol X) where X is the chemical formula).

M(air) = 28.97 g/mol = 1.654×10-4 lbf-s2/(in-mol) (Air is 78% N2)
M(N2) = 2 M(N) = 2(14.007 g N)/(1 mol N) = 28.014 g/mol = 1.5996×10-4 lbf-s2/(in-mol)
M(He) = 4.002602 g/mol = 2.285545×10-5 lbf-s2/(in-mol)

Gas Constants

Universal Gas Constant
R = 8.314462 N-m/(mol-K) = 3.406907 ft-lbf/(mol-°R) = 40.88288 in-lbf/(mol-°R)

Specific Gas Constant
Air: Rair = 53.343 ft-lbf/(lbm-°R) =   247,142 in2/(s2-°R)
N2:  RN2  = 55.163 ft-lbf/(lbm-°R) =   255,575 in2/(s2-°R)
He:  RHe = 386.086 ft-lbf/(lbm-°R) = 1,788,759 in2/(s2-°R)

 P V = Z m Rspecific T

Length

1 light-year = 9,460,730,472,580,800 m (Exact)
             ≈ 9.4607×1015 m
             ≈ 5.8786×1012 mi
             ≈ 63.241×103 AU (Astronmomical units)
             ≈ 0.3066 pc (parsecs)
The light-year is based on a Julian year of 365.25 days and a speed of light of 299,792,458 m/s.

Gravity, Mass and Force

go = 9.80665 m/s2 Standard Gravity (Wikipedia)

1 lbm = 0.453 592 37 kg by definition (Wikipedia)

From F = ma: 1 lbf = m×go = (0.45359237 kg/lbm)(9.80665 m/s2) = 4.4482216152605 N (kg-m/s2)

From m = F/go: lbf-s2/in = 1 lbf-s2/in (in/.0254 m) (lbm⋅9.80665 m/lbf⋅s2) (.453 592 37 kg / lbm) = 175.1268 kg 

1 Torr = 101,325/760 Pa
1 cmH2O = 98.0638 Pa
1 inH2O = 2.54 cmH2O
1 inHg = 3,386.389 Pa
1 mmHg = 13.5951(9.80665) Pa = 133.322387415 Pa
1 atm = 14.696 psi	(Approximate)

Work-Energy

1 BTU = 1,055.05585J (Approximate)
A BTU is defined as amount of heat required to raise the temperature of one 1 pound (0.454 kg) of liquid water by 1 °F (0.556 °C) at a constant pressure of one atmosphere.

Density, Specific Gravity and Specific Weight

Density, ρ = M/V

Specific gravity: s = ρ/ρw

Specific weight: γ = ρ⋅g

ρw = 1.00 gm/cm3 = 1000 kg/m3

ρw = 1000 kg/m3(lbf-s2/ 175.1268 kg-in)(.0254 m/in)3 = 9.357×10-5 lbf-s2/in4

Specific gravity is based on the density of water at various temperatures and depends on the industry using it. The American Petroleum Institute (API) uses a 60°F water density of 999.016 kg/m3. In chemistry, aqueous solutions typically use a maximum density (near 4°) of 999.972 kg/m3.

ρw = 999.016(9.35725468740217772E-8) = 9.34804714878977398E-5 lbf-s2/in4
ρw = 999.972(9.35725468740217772E-8) = 9.35699268427093046E-5 lbf-s2/in4

γw = ρw⋅g = 1000 kg/m3(9.80665 m/s2) (lbf-s2/175.1268 kg⋅in) (.0254 m/in)2)(12 in/ft)3 = 62.42796 lbf/ft3

Absolute/Dynamic Viscosity - μ

1 Pl = 1 Pa-s = 1 kg/m-s = 1 N-s/m2 (Poiseuille)
1 P = 1 gm/cm-s (Poise)
1 Pl = 10 P

1 cP = 10-3 N-s/m2
1 cP = (10-3 N-s/m2 / cP)(lbf / 4.4482216152605 N)(.0254 m / in)2 = 1.450×10-7 lbf-s/in2

Kinematic Viscosity - ν

μ = ρ⋅ν

1 St = 1 cm2/s (Stoke)
1 cSt = 1 cs = 1 mm2/s (centistoke)
1 cSt = 10-6 m2/s
1 cSt = 10-6 m2/s(in/.0254 m)2 = .00155 in2/s

Reference Material

The International System of Units (SI)
SI Standard Abbreviations