Second symbol

A lower-case s, the SI unit symbol for the second.

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Meanings

The lower-case letter s is the SI symbol for the second, the base unit of time. The SI does not abbreviate it 'sec', and it takes no plural.

Officially standardisedVerified fact
Denotes the second, the SI base unit of time.
Contexts: Mathematics
Officially standardisedVerified fact
Is written as a bare lower-case s with no full stop and no plural: 30 s, not 30 secs. A unit symbol is treated as a mathematical entity rather than an abbreviation of a word.
Contexts: Mathematics
Common modern usageVerified fact
Is defined by the caesium-133 hyperfine transition frequency, fixed at 9 192 631 770 hertz — the first SI unit to be tied to an atomic constant rather than to astronomy.
Contexts: Mathematics

Visual description

The lower-case Latin letter s: a single stroke curving one way and then the other, an open double curve with no straight segments.

A fuller structured visual breakdown is not yet documented for this symbol.

Confidence

IdentityHigh confidence: High confidence because the identity is defined by a current official standard, but multiple independent sources agree.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but multiple independent sources agree, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is defined by a current official standard, but multiple independent sources agree.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references, but multiple independent sources agree.

Sources

SI base units
Bureau International des Poids et Mesures · retrieved 2026-07-31
The seven base units and their symbols as published by the defining body. A summary page: the SI Brochure remains the full instrument.
Guide for the Use of the International System of Units (SI), NIST Special Publication 811
National Institute of Standards and Technology · retrieved 2026-07-31
A national metrology institute's guidance on applying the SI, including symbol formatting. Authoritative for usage rules in the United States; it interprets the SI rather than defining it.
The International System of Units (SI), 9th edition
Bureau International des Poids et Mesures · retrieved 2026-07-31
The defining document for SI unit names and symbols, including the capitalisation and spacing rules. It defines units; it says nothing about how a symbol is encoded in a character set, and nothing about non-SI units except where it lists those accepted for use with the SI.

Last reviewed 2026-08-01

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Units of measurement and their symbols

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Meanings

The lower-case letter s is the SI symbol for the second, the base unit of time. The SI does not abbreviate it 'sec', and it takes no plural.

Officially standardisedVerified fact

Denotes the second, the SI base unit of time.

Contexts: Mathematics

Officially standardisedVerified fact

Is written as a bare lower-case s with no full stop and no plural: 30 s, not 30 secs. A unit symbol is treated as a mathematical entity rather than an abbreviation of a word.

Contexts: Mathematics

Common modern usageVerified fact

Is defined by the caesium-133 hyperfine transition frequency, fixed at 9 192 631 770 hertz — the first SI unit to be tied to an atomic constant rather than to astronomy.

Contexts: Mathematics

Confidence

IdentityHigh confidence: High confidence because the identity is defined by a current official standard, but multiple independent sources agree.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but multiple independent sources agree, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is defined by a current official standard, but multiple independent sources agree.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references, but multiple independent sources agree.

Sources

SI base units
Bureau International des Poids et Mesures · retrieved 2026-07-31
The seven base units and their symbols as published by the defining body. A summary page: the SI Brochure remains the full instrument.
Guide for the Use of the International System of Units (SI), NIST Special Publication 811
National Institute of Standards and Technology · retrieved 2026-07-31
A national metrology institute's guidance on applying the SI, including symbol formatting. Authoritative for usage rules in the United States; it interprets the SI rather than defining it.
The International System of Units (SI), 9th edition
Bureau International des Poids et Mesures · retrieved 2026-07-31
The defining document for SI unit names and symbols, including the capitalisation and spacing rules. It defines units; it says nothing about how a symbol is encoded in a character set, and nothing about non-SI units except where it lists those accepted for use with the SI.

Last reviewed 2026-08-01