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Definition

A lower-case m has several possible meanings on a Safety Data Sheet. The most likely uses are:

• Mouse - this is used to indicate which kind of animal was used in toxicity testing. Usually written as a lower-case m. See an example under SDS Relevance below. RTECS uses the abbeviation mus for mouse.
• Molality, a unit of concentration. While this is correctly written in lower-case italics, m, remember that plain text files do not support italics. Do not confuse this with closely-related molarity, which is capitalized M.
• Meter - a metric unit of distance; generally unlikely to appear on an SDS as a distance unit except perhaps as a minimum safe distance.

Do not confuse m with m³ = cubic meter, a unit of volume, which can appear as m3 in plain text files that do not support sub- and superscript characters.

SDS Relevance

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One can usually determine the intended meaning of "m" on Safety Data Sheet by looking at the context in which it is used. For example:

• When used with toxicity values such as an LD₅₀, m usually refers to mouse. For example, "7,548 mg/kg (inhalation, m)"
• When used with respect to a solution concentration, a lower case m refers to molality and an upper case M refers to molarity.
• When used in reference to a distance, m usually means meters.
• When used in reference to a volume, m is usually written m³ or m3 for cubic meter.

Further Reading

• Metric Information and Conversions Home Page at the National Institute of Standards.
• More info about the metric system, including prefixes, at ChemTeam.
• M - What does M stand for? at TheFreeDictionary.com
• Abbreviations that start with the letter: M at Abbreviations.com.

See also: concentration units, distance units, RTECS, volume units.

Additional definitions from Google and OneLook.

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