This is a must-read for laboratory personnel! When it comes to these unit notations, 90% of people have fallen into traps with them.

When writing papers, recording data, or preparing reports in the laboratory, have you ever come across situations like these?
—The supervisor frowns while pointing at your data chart: “What does ‘MG’ mean here? It should be ‘mg’, right?”
— A lab mate (complains): “With your ‘ml’ and ‘PH’, don’t claim you’re a formally trained scientist!”
— The paper was rejected, and the review comment stated: The unit symbols are non-standard and need to be corrected in line with international standards.
Although the misnotation of units may seem like a trivial issue, it can undermine the credibility of rigorous experimental data or even lead to misinterpretation. Today, let’s sort out the most commonly used unit norms in laboratories to help you avoid unit-related pitfalls!
I.The Underlying Logic of Unit Nomenclature: The International System of Units (SI) as the Core
The most authoritative unit specification in laboratories is the International System of Units (SI). It defines seven base units (meter, kilogram, second, ampere, kelvin, mole, candela), along with a series of derived units and prefixes (used to denote multiples or fractions).
Remember two major principles:
There are strict rules for symbol case: Symbols for base units are lowercase (e.g., meter m, kilogram kg), but units named after scientists are capitalized (e.g., ampere A, joule J).
Prefixes cannot be used independently: Prefixes (e.g., kilo- k, milli- m) must be written together with unit symbols and cannot appear alone (e.g., “5 kilo” should be “5 k”, not “5 K”).
II.High-Frequency Lab Units List: Correct Notations + Common Mistakes

1. Length Units

2.Volume Units

Correct Notation	Common Incorrect Notations	Explanation
mL (milliliter)	ML, ml	“m” is lowercase, “L” is uppercase (internationally specified).
μL (microliter)	ul, μl	“μ” (Greek letter) should not be written as “u”; “L” should be uppercase.
L (liter)	l	Should be uppercase even when used alone to avoid confusion with the number “1”.

3. Mass Units

Correct Notation	Common Incorrect Notations	Explanation
g (gram)	G	Unit symbols are generally lowercase, unless named after a scientist.
kg (kilogram)	Kg, KG	“k” (kilo-) is lowercase, “g” (gram) is lowercase.
mg (milligram)	MG	“m” (milli-) is lowercase, “g” (gram) is lowercase.
μg (microgram)	ug, μG	“μ” (Greek letter) should not be written as “u”; “g” (gram) is lowercase.

4.Time Units

Correct Notation	Common Incorrect Notations	Explanation
s (second)	S	Unit symbol is lowercase.
min (minute)	Min, mins	Standard symbol is “min” (no plural “s”).
h (hour)	H, hr	Standard symbol is “h”.
d (day)	day, D	Standard symbol is “d”.

5. Concentration Units

Correct Notation	Common Incorrect Notations	Explanation
mol/L	M, mol/l	“M” is commonly used but non-standard; “L” should be uppercase.
mmol/L	mM	Same as above; “mM” is non-standard.
μg/mL	ug/ml	“μ” (Greek letter) should not be written as “u”; “L” should be uppercase (note: “mL” is the correct sub-unit here).
% (percentage)	％ (full-width symbol)	Use half-width symbol.

6. Temperature Units

Correct Notation	Common Incorrect Notations	Explanation
°C (degree Celsius)	℃, C, oC	Use the degree symbol “°” instead of “o” or plain “C”.
K (kelvin)	°K	No degree symbol is used for kelvin temperature.

 7. pH Units

Correct Notation	Common Incorrect Notations	Explanation
pH	PH, Ph	“p” is lowercase, and “H” is uppercase as specified.

8. Electrophoresis-Related Units

Correct Notation	Common Incorrect Notations	Explanation
V (volt)	v	Unit named after a scientist, capitalized first letter.
mA (milliampere)	MA, ma	“m” (milli-) is lowercase, “A” (ampere) is capitalized.
kV (kilovolt)	KV, Kv	“k” (kilo-) is lowercase, “V” (volt) is capitalized.

9. Radioactivity Units

Correct Notation	Common Incorrect Notations	Explanation
Bq (becquerel)	BQ, bq	“B” is uppercase, “q” is lowercase.
Gy (gray)	GY, gy	“G” is uppercase, “y” is lowercase.

10. Pressure Units

Correct Notation	Common Incorrect Notations	�� Explanation
Pa (pascal)	pa, PA	“P” is uppercase, “a” is lowercase.
kPa (kilopascal)	KPa, Kpa	“k” (kilo-) is lowercase, “P” is uppercase, “a” is lowercase.
MPa (megapascal)	Mpa, mPa	“M” (mega-) is uppercase, “P” is uppercase, “a” is lowercase; “mPa” denotes millipascal.
bar	Bar, BAR	All lowercase (non-scientist-named unit).
mmHg (millimeter of mercury)	mm Hg, MMHG	Written without space; “mm” is lowercase, “Hg” is uppercase.
atm (standard atmosphere)	ATM, Atm	All lowercase.

In the preparation of experimental reports, recording of experimental data, and daily communication, strictly following the standardized notation of these units can effectively avoid misunderstandings and ensure the rigor and scientificity of experimental work. Everyone must develop good habits of unit notation when operating in the laboratory!

Forward this to your lab mates and let’s standardize together!