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KnownUnitQ[expr]

returns True if expr is a canonical unit, and False otherwise.

KnownUnitQ[expr,dims]

gives True if expr is a canonical unit with physical dimensions dims, and False otherwise.

Details
Details and Options Details and Options
Examples  
Basic Examples  
Scope  
Properties & Relations  
Possible Issues  
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KnownUnitQ

KnownUnitQ[expr]

returns True if expr is a canonical unit, and False otherwise.

KnownUnitQ[expr,dims]

gives True if expr is a canonical unit with physical dimensions dims, and False otherwise.

Details

  • KnownUnitQ has attribute HoldFirst.
  • KnownUnitQ[expr,dims] returns True if expr is a canonical unit and is compatible with dims.
  • Dimensional specification dims may be a list of unit dimensions, a QuantityVariable, a Quantity or a string representing a quantity variable or unit dimension.

Examples

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Basic Examples  (2)

Test whether an input expression is a canonical unit:

Wolfram Language code: KnownUnitQ["Feet"]
Wolfram Language code: KnownUnitQ["Feet" ^ 2 / "Farads"]
Wolfram Language code: KnownUnitQ["Foo"]

Test if an expression is a time unit:

Wolfram Language code: KnownUnitQ["Seconds", "Time"]
Wolfram Language code: KnownUnitQ["Meters", "Time"]

Scope  (9)

Units represented by a single string:

Wolfram Language code: KnownUnitQ["Meters"]
Wolfram Language code: KnownUnitQ["Siemens"]

Products of known units:

Wolfram Language code: KnownUnitQ["Newtons" * "Meters"]
Wolfram Language code: KnownUnitQ["Watts" / "Meters" ^ 2]

KnownUnitQ returns True for valid IndependentUnit specifications:

Wolfram Language code: KnownUnitQ[IndependentUnit["myUnit"]]
Wolfram Language code: KnownUnitQ[IndependentUnit["Unit1"] / IndependentUnit["Unit2"] ^ 3]

It returns False for invalid IndependentUnit specifications:

Wolfram Language code: KnownUnitQ[IndependentUnit[1]]
Wolfram Language code: KnownUnitQ[IndependentUnit[unit]]

MixedUnit specifications of compatible units:

Wolfram Language code: KnownUnitQ[MixedUnit[{"Yards", "Centimeters"}]]

Incompatible units do not produce a valid MixedUnit specification:

Wolfram Language code: KnownUnitQ[MixedUnit[{"Seconds", "Centimeters"}]]

DatedUnit specifications:

Wolfram Language code: KnownUnitQ[DatedUnit["USDollars", 1990]]
Wolfram Language code: KnownUnitQ[DatedUnit["Euros", Today]]

Prefixes are dimensionless known units:

Wolfram Language code: KnownUnitQ["Centi"]
Wolfram Language code: KnownUnitQ["Mega"]

Dimension specifications may be a list of unit dimensions, QuantityVariable, Quantity or string:

Wolfram Language code: KnownUnitQ["Meters", {{"LengthUnit", 1}}]
Wolfram Language code: KnownUnitQ["Meters", Height]
Wolfram Language code: KnownUnitQ["Meters", Quantity[10, "Feet"]]
Wolfram Language code: KnownUnitQ["Meters", "LengthUnit"]
Wolfram Language code: KnownUnitQ["Meters", "Depth"]

KnownUnitQ returns False if the first argument is not a canonical unit expression:

Wolfram Language code: KnownUnitQ[x, Acceleration]

KnownUnitQ returns False if the second argument is not a recognized dimension specification:

Wolfram Language code: KnownUnitQ["Meters" / "Seconds", "foo"]
Wolfram Language code: KnownUnitQ["Meters" / "Seconds", x]

Properties & Relations  (2)

KnownUnitQ has attribute HoldAll:

Wolfram Language code: x = "Meters"
Wolfram Language code: KnownUnitQ[x]
Wolfram Language code: KnownUnitQ["Meters" / "Meters"]

A MixedUnit specification is valid if it contains compatible units:

Wolfram Language code: KnownUnitQ[MixedUnit[{"Centimeters", "Meters", "Feet"}]]
Wolfram Language code: CompatibleUnitQ[{"Centimeters", "Meters", "Feet"}]

Possible Issues  (2)

Quantity can interpret a non-canonical unit, converting it to its canonical form:

Wolfram Language code: Quantity[1, "ft"]
Wolfram Language code: InputForm[%]

KnownUnitQ does not accept non-canonical units:

Wolfram Language code: KnownUnitQ["ft"]

But it does accept their canonical form:

Wolfram Language code: KnownUnitQ["Feet"]

Dimension specifications may not be a unit:

Wolfram Language code: KnownUnitQ["Feet", "Meters"]
Wolfram Research (2012), KnownUnitQ, Wolfram Language function, https://reference.wolfram.com/language/ref/KnownUnitQ.html (updated 2024).

Text

Wolfram Research (2012), KnownUnitQ, Wolfram Language function, https://reference.wolfram.com/language/ref/KnownUnitQ.html (updated 2024).

CMS

Wolfram Language. 2012. "KnownUnitQ." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2024. https://reference.wolfram.com/language/ref/KnownUnitQ.html.

APA

Wolfram Language. (2012). KnownUnitQ. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/KnownUnitQ.html

BibTeX

@misc{reference.wolfram_2026_knownunitq, author="Wolfram Research", title="{KnownUnitQ}", year="2024", howpublished="\url{https://reference.wolfram.com/language/ref/KnownUnitQ.html}", note=[Accessed: 13-June-2026]}

BibLaTeX

@online{reference.wolfram_2026_knownunitq, organization={Wolfram Research}, title={KnownUnitQ}, year={2024}, url={https://reference.wolfram.com/language/ref/KnownUnitQ.html}, note=[Accessed: 13-June-2026]}