The Metric System, Abbreviations, and Conversions
for Common Units of Measure
We present the most common abbreviations for units of measure used in general biology.
General Rules for Abbreviating. Units of Measure
- Always abbreviate units when reporting numerical information.
- Unless otherwise noted, singular and plural units are abbreviated the same.
- Percent is not abbreviated, but is symbolized by the familiar "%" symbol.
- Always put a space between the number and unit, e.g., 203.65 m, 457 um
- When do you abbreviate units vs. spelling out the unit(s) as word(s)?
- Abbreviate units when you are reporting a numerical value:
"The maximum depth achieved by the ROV was 124 m approximately 2.3 km due south of Pt. Lobos."
- Spell out the unit as a word when using it in a non-numerical context, e.g.,
"All measurements were made in millimeters unless otherwise indicated."
- When starting a sentence with a number and unit, both must be spelled out as words (this is something
to avoid, if possible), e.g.,
"One thousand six hundred and eighty-seven kilograms of ground beef were randomly sampled and
tested for E.coli contaminants between 21 August and 21 November, 1995."
The Metric System
The Metric System of measurement is the standard used by most scientific disciplines. The system is
based upon measures of distance (in meters), volume (in liters), and mass (in grams). Scales of
measurements increase or decrease as multiples of ten which facilitates expression of measurement
values using the decimal system.
The table below shows the most common prefixes and their relative magnitudes.
Note that web browsers do not support use of superscripts and subscripts very well, so the notation
10^2 means "10 to the power of 2, or 10 squared".
Similarly, the notation 10-2 should be read as "10 to the power of -2".
Prefix Scientific Notation Decimal equivalents Example Units
kilogram (kg);
kilo- (k) = 10^3 = 1000
kilometer (km)
centi- (c) = 10-2 = 0.01 centimeter (cm)
milligram (mg);
milli- (m) = 10-3 = 0.001
millimeter (mm)
microgram (ug)
micro- (u) = 10-6 = 0.000001
microliter (uL)
nanogram (ng)
nano- (n) = 10-9 = 0.000000001
nanoamperes (nA)
picogram (pg)
pico- (p) = 10-12 = 0.000000000001
picoamperes (pA)
Conversions
Units of Distance and Length
Metric Equivalents
1 km = 1000 m; 1 m = 100 cm = 1000 mm = 10^6 um = 10^9 nm
multiplied by = English Unit
Metric Unit
millimeters 0.0394 inches (in)
centimeters 0.394 inches
centimeters 0.0328 feet (ft)
meters 39.4 inches
meters 3.28 feet
meters 1.1 yards (yd)
kilometers 3,281 feet
kilometers 0.621 miles (mi)
English Equivalents
1 mi = 1,760 yd = 5,281 ft; 1 yd = 3 ft = 36 in
English Unit multiplied by = Metric Unit
inches (in) 25.4 millimeters
inches 2.54 centimeters
inches 0.254 meters
feet (ft) 30.48 centimeters
yards (yd) 91.44 centimeters
yards 0.9144 meters
miles (mi) 1.609 kilometers
Units of Mass
Metric Equivalents
1 mt (metric ton) = 1000 kg = 2,205 lb
1 kg = 1000 g = 2.205 lb = 35.2802 oz
1 g = 1000 mg = 10^6 ng = 10^9 pg
Metric Unit Multiplied by = English Unit
gram (g) 0.035 ounces (oz)
kilogram (kg) 2.2 pounds (lb)
metric ton (mt) 1.102 ton (t)
English Equivalents
1 ton = 2000 lb = 907.2 kg or 0.9072 mt
1 lb = 16 oz = 0.4536 kg = 453.6 g
English Unit Multiplied by = Metric Unit
ounce (oz) 28 grams (g)
pound (lb) 0.4536 kilograms (kg)
tons (t) 0.9072 metric tons (mt)
Units of Volume
Metric Equivalents
1 cm^3 (or cc) = 1000 mm^3 = 0.061 in^3
1 m^3 = 10^6 cm^3 = 61,024 in^3 = 35.31 ft^3 = 1.308 yd^3
Multiplied by = English Unit
Metric Unit
cubic centimeters
0.061 cubic inches (in^3)
(cm^3)
cubic meters (m^3) 35.31 cubic feet (ft^3)
cubic meters 1.308 cubic yards (yd^3)
English Equivalents
1 ft^3 = 1,728 in^3 = 28,317 cm^3 = 0.02832 m^3
1 yd^3 = 27 ft^3 = 0.7646 m^3
English Unit Multiplied by = Metric Unit
cubic inches 16.393 cubic centimeters
cubic feet 0.03 cubic meters
cubic yards 0.76 cubic meters
Units of Liquid Volumes
Metric Equivalents
1 L = 1000 ml = 2.113 pt (pints) = 1.06 qt (quarts) = 0.264 US
gal
1 ml (or cm^3) = 1000 ul = 0.03 fl oz (fluid ounces)
Multiplied by = English Unit
Metric Unit
milliliters (ml) 0.02957 fluid ounces (fl oz)
liters (L) 2.13 pints (pt)
liters (L) 1.0567 quarts (qt)
English Equivalents
1 US gal = 4 qt = 8 pt = 128 fl oz = 3.785 L
1 qt = 2 pt = 32 fl oz = 946.4 ml or 0.9464 L
1 pt = 16 fl oz = 473.2 ml or 0.213 L
1 fl oz = 29.57 ml
English Unit Multiplied by = Metric Unit
teaspoons (tsp) 5 milliliters (ml)
tablespoons (tbsp) 15 milliliters
fluid ounces (fl oz) 29.57 milliliters
cups (c) 0.24 liters (L)
pints (pt) 0.4732 Liters
quarts (qt) 0.9464 Liters
US gallons (US gal) 3.785 Liters
Units of Area
Metric Equivalents
1 km^2 = 100 ha = 1,000,000 m^2 = 270 A (acres) = 0.3861
mi^2
1 ha (hectare) = 10,000 m^2 = 107,600 ft^2 = 2.471 A
1 m^2 = 10,000 cm^2 = 1,000,000 mm^2 = 1,550 in^2 = 1.196
yd^2
1 cm^2 = 100 mm^2 = 0.155 in^2
1 mm^2 = 1,000,000 um^2
Multiplied by = English Unit
Metric Unit
centimeters squared 0.155 inches squared
meters squared 1.196 Yards squared
kilometers squared 0.3861 Miles squared
English Equivalents
1 mi^2 = 640 A = 27,878,400 ft^2 = 259 ha = 2.59 km^2
1 A = 4,840 yd^2 = 43,560 ft^2 = 4,407 m^2 = 0.405 ha
1 yd^2 = 9 ft^2 = 1296 in^2 = 8,361 cm^2 = 0.836 m^2
1 ft^2 = 144 in^2 = 929 cm^2
1 in^2 = 6.452 cm^2
Multiplied by = Metric Unit
English Unit
inches squared 6.452 centimeters squared
feet squared 0.0929 meters squared
yards squared 0.836 meters squared
acres (A) 0.405 hectares (ha)
miles squared 2.59 kilometers squared
Units of Temperature
Temperature Equivalents
K = Kelvin || C = Celcius || F = Fahrenheit
0 K = -273.15 C = absolute zero (no molecular motion)
273.15 K = 0 C = 32 F = freezing point of water/ melting point
of ice
373.15 K = 100 C = 212 F = boiling point of water
Fahrenheit (F) to Celcius (C) Conversion
(degrees F - 32) x 5/9 = degrees C
Celcius (C) to Fahrenheit (F) Conversion
(degrees C x 9/5 ) + 32 = degrees F
Units of Concentration
Concentration usually refers to a mass/volume relationship.
Percent (%) = grams solute / 100 ml solvent;
To convert to molar concentration multiply grams by
10, then divide by the formula weight (FW) of the
solute.
= moles solute per liter of solvent
For example,
1 M = 1 mole/liter; where,
1 mole = 6.023 x 10^23 molecules
Molarity (M) = 1 molecular weight (MW)
~ 1 formula weight (FW)
Molarity may also be expressed as mM (millimolar),
where 1 mM equals 10-3 M, when working with low
concentrations.
= grams total solutes per kg of seawater
Salinity is usually expressed as "parts per thousand" =
ppt.
Salinity
Coastal seawater has approximately 30-32 g solutes per
kg = 30-32 ppt salinity.
Units of pH
In contrast to other units, report pH with the unit before the number: e.g., pH 8.2
Units of Time
The most frequent units time used in the biological sciences are:
Years yr
Days d
Hours h
Minutes min
Seconds sec or s
Milliseconds msec
