Plus-minus sign (±)
The plus-minus sign (±) means “plus or minus”. In a measurement it gives the margin either side of a value: 6.72 ± 0.01 grams means between 6.71 and 6.73 grams.
How to read it
It is read “plus or minus”. In algebra it stands for two answers at once, one with plus and one with minus; OpenStax reads the quadratic formula as negative b “plus or minus” a square root, all over 2a. In science it marks uncertainty: OpenStax’s Chemistry weighs a quarter at about 6.72 grams “with a nominal uncertainty in the measurement of ± 0.01 gram”. The code point is U+00B1, PLUS-MINUS SIGN.
Also searched as: ±, plus minus symbol, plus or minus symbol.
Look-alikes
∓ (U+2213) is the minus-or-plus sign, with the minus on top. Unicode also records another name for ±: biquintile, an astrological aspect of 144°.
How NIST writes it with units
NIST’s SI guide writes 63.2 m ± 0.1 m or (63.2 ± 0.1) m, and not 63.2 ± 0.1 m, so that the unit clearly belongs to both numbers. NIST’s guide to measurement uncertainty writes a result as Y = y ± U, meaning the true value is believed to lie between y − U and y + U.
More math symbols
Browse symbols drawn with crosses or lines.
Sources
- C1 Controls and Latin-1 Supplement (code chart, Range 0080–00FF), The Unicode Standard, Version 18.0, Unicode Consortium, Latin-1 Supplement, 00B1
- Mathematical Operators: Range 2200–22FF (code chart), The Unicode Standard, Version 18.0, Unicode Consortium, Mathematical Operators, 2213
- Intermediate Algebra 2e, 9.3 Solve Quadratic Equations Using the Quadratic Formula, OpenStax (Rice University), Solve Quadratic Equations Using the Quadratic Formula
- Chemistry 2e, 1.5 Measurement Uncertainty, Accuracy, and Precision, OpenStax (Rice University), Measurement uncertainty
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811 (2008), National Institute of Standards and Technology, Sec. 7.7
- Uncertainty of Measurement Results: Expanded uncertainty and coverage factors, The NIST Reference on Constants, Units and Uncertainty, U.S. National Institute of Standards and Technology, Expanded uncertainty
- Earliest Uses of Symbols of Operation, Jeff Miller, Earliest Uses of Various Mathematical Symbols, MacTutor History of Mathematics, University of St Andrews, Other symbols of operation
- A History of Mathematical Notations, Vol. I: Notations in Elementary Mathematics, Florian Cajori (Chicago: Open Court, 1928); full text of the Wellcome Collection copy, Internet Archive, §§ 210, 262
Last reviewed September 30, 2026 by Rory Hansen. How we research