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Encyclopedia > Parts per million

Parts per million (ppm) is a measure of concentration that is used where low levels of concentration are significant. The ppm value is equivalent to the absolute fractional amount multiplied by one million (106). It is a term with several variants in meaning, so the meaning should be made clear if this term is used. Concentration is a very common concept used in chemistry and related fields. ... One million (1000000), one thousand thousand, is the natural number following 999999 and preceding 1000001. ...

Parts per million is related to percent (parts per hundred) as follows:

1% = 10,000 ppm or 1/100 = 10,000/1,000,000.

Senses of parts per million

The metric system is the most convenient way to express this since metric units go by steps of ten, hundred and thousand. For example, a milligram is a thousandth of a gram and a gram is a thousandth of a kilogram. Thus, a milligram is a thousandth of a thousandth, or a millionth of a kilogram. A milligram is one part per million of a kilogram thus, one part per million (ppm) by mass is the same as one milligram per kilogram. Just as part per million is abbreviated as ppm, a milligram per kilogram has its own symbolic form -- mg/kg, which unlike ppm is unambiguous. The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ...

  • By mass:
  • By volume: (ppmv)
    • one millilitre (or cubic centimetre) in a cubic metre (or kilolitre) is 1 ppm by volume. For most gases (those behaving much like an ideal gas) this is numerically equivalent to µmol/mol on the basis of molecules (not atoms). See Avogadro's law.
  • By mass/volume ratio for dilute aqueous solutions (ppm w/v or ppm m/v):
    • 1 litre (L) of water has mass of approximately 1 kg1, so 1 mg/L is, loosely speaking, 1 ppm, for small concentrations in a water solution2.
  • By number of particles or moles:
    • one micromole per mole can also be called 1 ppm.

Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ... The milligram (symbol mg) is an SI unit of mass. ... The international prototype, made of platinum-iridium, which is kept at the BIPM under conditions specified by the 1st CGPM in 1889. ... Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ... The gram or gramme, symbol g, is a unit of mass, and is defined in the SI system of units as one one-thousandth of a kilogram (i. ... A tonne (also called metric ton) is a non-SI unit of mass, accepted for use with SI, defined as: 1 tonne = 103 kg (= 106 g). ... The millilitre (ml or mL, also spelt milliliter) is a metric unit of volume that is equal to one thousandth of a litre. ... The cubic metre (symbol m³) is the SI derived unit of volume. ... An ideal gas or perfect gas is a hypothetical gas consisting of identical particles of negligible volume, undergoing perfectly elastic collisions, with no intermolecular forces and no intramolecular storage of energy. ... In 1811 Amedeo Avogadro stated the hypothesis which we now call Avogadros law: (See: this site for an English translation of his 1811 paper). ... Drinking water This article focuses on water as we experience it every day. ... The litre (or liter in US) is a metric unit of volume. ... Water (from the Old English word wæter) is a colorless, tasteless, and odorless substance that is essential to all known forms of life and is known also as the most universal solvent. ... The mole (symbol: mol) is one of the seven SI base units and is commonly used in chemistry. ...


Examples of situations where parts per million are an appropriate measure include:

Natural abundance refers to the prevalence of different isotopes of an element as found in nature. ... Microminerals (also known as trace elements) are micronutrients that are chemical elements. ... Earth cutaway from core to exosphere. ... Pollutants are substances which directly or indirectly damage us or the environment. ...

Inexact analogues

  • one square centimeter in 1000 square feet is about .95 ppm
  • one two-parent, two-child family in a city of about 4 million people is roughly 1 ppm
  • one CD in the 1.57-million disc3 FreeDB catalogue is nearly 2/3 ppm

freedb is a database of compact disc track listings where all the content is under the GNU General Public License. ...

Related units

A percentage is a way of expressing a proportion or a fraction as a whole number. ... A permille or per mille is a tenth of a percent or one part per thousand. ... Usage in this encyclopedia One billion = 109 unless otherwise noted. ... The numeral trillion refers to one of two number values, depending on the context of where and how it is being used. ...

NIST caution

According to the U.S. National Institute of Standards and Technology (NIST) Guide for the Use of the International System of Units (SI), "the language-dependent terms part per million, part per billion, and part per trillion ... are not acceptable for use with the SI to express the values of quantities." NIST's Guide for the Use of the International System of Units (SI) (http://physics.nist.gov/Pubs/SP811/sec07.html#7.10.3) has examples of alternative expressions. As a non-regulatory agency of the United States Department of Commerce’s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ...


  1. Exactly one kg of pure water at maximum density (~4°C) and standard pressure was the definition of a litre from 1901 to 1964; today the litre is defined as exactly 1 dm³, the distinction being whether it is calibrated to the international standard kilogram (http://www.sizes.com/units/kilogram.htm) or the international standard meter (http://www.sizes.com/units/meter.htm), which are defined without reference to one another.
  2. Properly speaking it is approximately 1 ppm by mass or by weight in solution. When solids dissolve, they can increase or decrease the total volume they occupy, and even increase or decrease the total volume of the solution. Adding 1 ppm by weight will rarely produce a solution that is 1 ppm by volume to the same precision. The notation ppm w/v or ppm m/v demonstrates the exact nature of the ratio and is therefore the most precise.
  3. As of January 2005.

  Results from FactBites:
One part per billion is the equivalent of one drop of impurity in 500 barrels of water.
A milligram is one part per million of a kilogram thus, one part per million (ppm) is the same as one milligram per kilogram.
Similarly, a part per billion of a solid in a liquid is equal to a ug/l.
Parts Per Million: Part 1 (704 words)
Parts per million (abbreviated ppm) is one part in a million parts.
One pound of sugar in 120,000 gallons of water is one part per million, or one ten thousandth of a percent.
Parts per million is an easier, better term to visualize than percentages for concentrations in water.
  More results at FactBites »



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