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## The Metric System, Abbreviations, and Conversions for Common Units of Measure

### On Line Unit Converter: http://www.easyunitconverter.com/

| Rules for Use of Abbreviations | The Metric System |
| Length and Distance | Volume | Liquid Volumes | Mass | Area | Temperature | Pressure |
| Humidity | Concentration | Salinity | pH | Time |

This page presents the most common abbreviations you will use in general biology, especially those for units of measure.

### 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 represented by the familiar "%" symbol.
• Always put a space between the number and unit, e.g., 203.65 m, 457 um
• pH: The proper method for reporting pH is to place the unit before the number (pH 7); never insert the word "of" between the unit and number and avoid splitting the unit and number within a sentence - they should always go together.
• 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 kilo- (k) = 10^3 = 1000 kilogram (kg); kilometer (km) centi- (c) = 10-2 = 0.01 centimeter (cm) milli- (m) = 10-3 = 0.001 milligram (mg); millimeter (mm) micro- (u) = 10-6 = 0.000001 microgram (ug)  microliter (uL) nano- (n) = 10-9 = 0.000000001 nanogram (ng) nanoamperes (nA) pico- (p) = 10-12 = 0.000000000001 picogram (pg)  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 Metric Unit multiplied by = English Unit millimeters centimeters centimeters meters meters meters kilometers kilometers 0.0394 0.394 0.0328 39.4 3.28 1.1 3,281 0.621 inches (in) inches feet (ft) inches feet yards (yd) feet 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) inches inches feet (ft) yards (yd) yards miles (mi) 25.4 2.54 0.254 30.48 91.44 0.9144 1.609 millimeters centimeters meters centimeters centimeters meters kilometers

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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)

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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 Metric Unit Multiplied by = English Unit cubic centimeters (cm^3) 0.061 cubic inches (in^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

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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) Metric Unit Multiplied by = English 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

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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 Metric Unit Multiplied by = English 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 English Unit Multiplied by = Metric 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

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Units of Temperature

 Temperature Equivalents K = Kelvin || C = Celsius || 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 Celsius (C) Conversion (degrees F - 32) x 5/9 = degrees C Celsius (C) to Fahrenheit (F) Conversion (degrees C x 9/5 ) + 32 = degrees F

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Units of Pressure - On-Line Unit Converter

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Units of Humidity

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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. Molarity (M) = moles solute per liter of solvent For example, 1 M = 1 mole/liter; where, 1 mole = 6.023 x 10^23 molecules = 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. Salinity = grams total solutes per kg of seawater Salinity is usually expressed as "parts per thousand" = ppt. 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. When reporting a series of pH values, report the unit only at the beginning: e.g., ...buffered to pH 3, 5, 7, and 9....

#### 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

Modified 3-26-08
Department of Biology, Bates College, Lewiston, ME 04240