 SYSTEMS OF UNITS -- THE BASICS
Units of measurement cannot be avoided in the practice of petrophysics, nor in our ordinary life. Different systems are used in different countries, in different industries, and even in different cultures in the same communities -- gets confusing. One of the best known and least used unit of measurement is the cubit. It is defined as the distance from the elbow to the tip of the longest finger. My personal cubit is right on 18 inches. Yours is probably different. Similarly, the English foot is slightly smaller than the French foot -- the respective Kings had different sized feet. To get around these problems, standards have been established and most countries except the USA have adopted them for personal, commercial, and scientific arenas.

This page covers most of what you need to survive in the oil and gas industry. Descriptions of Systeme Internatuinal or SI units, oilfield units, and conversions between them follow this introduction,

Some commonly used words that predate the SI units have different meanings in different parts of the world, and some abbreviations (for example the letter "M") have more than one meaning. Here is a ;list of the common problem words:

American           British/French/German    Prefix    Abbreviation     Factor
thousand            thousand                          Kilo       k                         10^3
million               million                              Mega    M                         10^6
billion                  milliard                            Giga      G                         10^9
trillion               billion                               Tera       T                         10^12
quintillion         trillion                               Exa        E                         10^18
sextillion               –                                   Zetta      Z                          10^21

In many industries, the Roman numeral M, meaning 1000 and MM meaning 1 million were, and still are, widely used, not to be confused with the SI prefix M, meaning 1 million. Sometimes MM is shown in lower case as mm (for example mmcf/d, meaning 1 million cubic feet per day), not to be confused with the SI unit mm (millimeter). The SI prefix k, meaning 1000, is often written as a capital letter K, in keeping with the capitalization of many other prefixes for positive powers of 10 (for example M, G, T. etc).

There is no shortage of obsolete units of measurement, some still in wide use, such as nautical miles and knots in the ship and airline transportation. Some may be found in surveying, especially in non-English speaking countries. Here are some of the most common:

1 nautical mile = 1.1508 miles = 1/60 degree of latitude on Earth
1 knot = 1.1508 miles per hour
1 fathom = 6.0 feet = 1.829 meters
1 league = 5.556 km = 3.452 miles = 3 nautical miles
1 league (area) = 4.428 acres = 1.792 hectares

Some older survey plats may use these tems:
1 rod = 16.5 feet = 0.25 chains = 1 perch = 1 pole
1 chain = 4 rods = 20.17 meters = 66 feet = 100 links = 1/80 mile
1 furlong = 10 chains = 201.168 meters = 660 feet = 1/8 mile

These French measurements nay be found in Quebec an Louisiana and other early French settlements in the Americas.
1 pied = 1.0 French foot = 12.789 inches = 0.3248 meters = 1.0657 feet
1 loise = 6.0 pied = 1.949 meters = 6.394 feet
1 perche = 3 loise = 18.0 pieds = 5.847 meters = 19.183 feet
1 arpent = 10 perches = 30 loise = 180 pieds = 58.47 meters = 191.83 feet
1 arpent (area) = 3418.9 sq meters = 0.845 acres = 36 800 sq feet

Unfortunately, much of the work done in the oilfields uses a mixed set of units composed of British units (called English units in this Handbook) , CGS Units (an early form of metric units), and SI Units (called Metric units in this Handbook). Examples of English units are the foot, mile, and pound. Examples of Metric units are the meter, kilometer, and kilogram. Conversion back and forth between sets of units is a constant task for a petrophysicist.

A lengthy list of conversions is available at the bottom of this page. A useful freeware units conversion calculator can be downloaded HERE. This is an executable (.EXE) wrapped in a .ZIP file and may be blocked by your security settings. INTERNATIONAL SYSTEM OF UNITS (SI)
SI units are widely used in scientific work. All the SI fundamental units and derived units are listed on this page, as well as the universal constants. Prefixes are applied to the SI names of units to indicate multipliers of the basic unit

SI Prefixes
Factor Name  Symbol
1024 yotta Y
1021 zetta Z
1018 exa E
1015 peta P
1012 tera T
109 giga G
106 mega M
103 kilo k
102 hecto h
101 deka da

Factor Name  Symbol
10-1 deci d
10-2 centi c
10-3 milli m
10-6 micro µ
10-9 nano n
10-12 pico p
10-15 femto f
10-18 atto a
10-21 zepto z
10-24 yocto y

LIST OF SI UNITS
UNIT SYMBOL DERIVATION BASE UNITS REPRESENTING
ampere A -- A electric current
becquerel Bq 1/s s-1 activity
candela cd -- cd luminous intensity
coulomb C A s A s charge
farad F A s/V kg-1 m-2 s4 A2 capacitance
gray Gy J/kg m2 s-2 absorbed dose
henry H V s/A kg m2 s-2 A-2 inductance
hertz Hz 1/s s-1 frequency
joule J N m kg m2 s-2 energy
kelvin [footnote 1] K -- K temperature
kilogram kg -- kg mass
lumen lm cd sr cd sr luminous flux
lux lx lm/m2 cd sr m-2 illumination
metre m -- m length
mole mol -- mol amount of substance
newton N kg m/s2 kg m s-2 force
ohm O [footnote 2] V/A kg m2 s-3 A-2 resistance
pascal Pa N/m2 kg m-1 s-2 pressure
second s -- s time
siemens S 1/O kg-1 m-2 s3 A2 electric conductance
sievert Sv J/kg m2 s-2 dose equivalent
steradian sr -- sr solid angle
tesla T Wb/m2 kg s-2 A-1 magnetic flux density
volt V W/A kg m2 s-3 A-1 voltage
watt W J/s kg m2 s-3 power
weber Wb V s kg m2 s-2 A-1 magnetic flux

Non-SI unit approved for use with SI.
UNIT SYMBOL Value in SI Units
minute min 60 s
hour h 60 min = 3600 s
day d 24 h = 86 400 s
arcminute ', arcmin (1/60) deg = (pi/10 800) rad
arcsecond ", arcsec (1/60)' = (pi/648 000) rad
litre l, L [footnote 4] 1 dm3 = 10-3 m3
tonne t 103 kg
electronvolt eV (1.602 177 33 +- 0.000 000 49) x 10-19 J
unified atomic mass unit u (1.660 540 2 +- 0.000 001 0) x 10-27 kg
nautical mile -- 1852 m
knot -- 1 nautical mile per hour = (1852/3600) m/s
angstrom A [footnote 5] 10-10 m
are a 1 dam2 = 102 m2
hectare ha 104 m2
barn b 10-28 m2
bar bar 105 Pa
gal Gal 10-2 m/s2
curie Ci 3.7 x 1010 Bq
roentgen R 2.58 x 10-4 C/kg UNIVERSAL CONSTANTS (SI Units) OILFIELD UNITS CONVERSION TABLE