25
25 is a perfect square (5²) and a quarter of 100, which is why a 25th anniversary is a silver jubilee. As a date, 25 December is Christmas Day.
Where 25 fits
Why 25 is special
25's mathematical identity (5²) and its everyday role as a quarter (of 100, of a dollar, of a century) make it one of the most practically useful square numbers — it's also the atomic number of manganese, a metal essential to steelmaking.
Same number, different meanings
How 25 is understood across different contexts — never implying one meaning because of another.
- Mathematics
25's mathematical identity (5²) and its everyday role as a quarter (of 100, of a dollar, of a century) make it one of the most practically useful square numbers — it's also the atomic number of manganese, a metal essential to steelmaking.
- Religion & belief
25 December is Christmas Day, observed in Christian communities worldwide and as a public holiday in many countries; churches following the Julian calendar observe it on 7 January by the Gregorian reckoning. The date is a liturgical convention rather than a recorded birth date — the New Testament gives no date, and 25 December is first attested as the feast in fourth-century Rome. Churches that retain the Julian calendar, including several Orthodox churches, celebrate the same feast thirteen days later by Gregorian reckoning.
- Science
There are roughly 25 trillion red blood cells in an adult human body (adults). About 2.4 million are made every second, and each lasts around 120 days.
- Technology & computing
There are about 25 thousand international standards published by ISO. Figure as of 2024. Covering everything from screw threads to management systems. Almost none is legally binding on its own; standards acquire force when a contract or a regulation names one.
- Culture
A 25th wedding anniversary is traditionally called a "silver" anniversary in the Western anniversary-naming convention.
- Law & regulation
Twenty-five is the minimum age the US Constitution sets for the House of Representatives, against 30 for the Senate and 35 for the presidency — seniority by chamber rather than three separately reasoned thresholds. It is also the age below which most car hire firms charge a young-driver surcharge or refuse hire.
Factors & digit properties
- Divisors (3)
- 1, 5, 25
- Prime factorisation
- 5^2
- Digit sum
- 7
- Digital root
- 7
Representations
- Decimal
- 25
- Scientific notation
- 2.500 × 10^1
Roman numerals
X X V
Binary
1 1 0 0 1
1 × 16 + 1 × 8 + 0 × 4 + 0 × 2 + 1 × 1 = 25
Octal
3 1
3 × 8 + 1 × 1 = 25
Hexadecimal
1 9
1 × 16 + 9 × 1 = 25
Read as powers of two: 16 + 8 + 1 = 25.
In historical numeral systems
Egyptian
2 hobbles, 5 strokes
2 × 10 + 5 × 1 = 25. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
2 corner wedges + 5 vertical wedges
25 fits in a single sexagesimal place: 2 corner wedges + 5 vertical wedges.
Greek (Ionic)
kappa, then epsilon, marked as a numeral
kappa-epsilon + keraia
kappa + epsilon written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
kaf, then he
kaf-he
kaf (20) + he (5) = 25, written in descending order.
Chinese numerals
èr shí wǔ
èr shí wǔ
二 before 十 multiplies it: 2 tens. 五 after it adds 5. The written form mirrors the arithmetic — "èr shí wǔ". The financial (anti-fraud) form is 貳拾伍.
Maya
1 dot (upper, twenties place) over 1 bar (lower, units place)
1 × 20 + 5 = 25. Places stack vertically with the smallest at the bottom, so the upper group is worth twenty times the lower.
Systems that simply cannot reach this value are left out. Where a script needs a font most readers do not have, the reading is given instead of the glyphs — see number systems for each system in full.
Other mathematical patterns
- Deficient number
- Powerful number
- Automorphic number
- Semiprime
- Lucky number (mathematical sieve)
Related numbers & connections
25 is a factor of 50 (25 × 2 = 50).
View 50 →25 appears in Numbers in living things, the topic covering numbers that carry a documented biology or natural-history fact.
25 relays mail between servers and 587 accepts new mail from a person. Splitting them is what lets a provider block outbound 25 to suppress spam without breaking ordinary mail clients.
View 587 →Mathematically related
Numbers Around Us
- appears inLiving things
why?
Strength 0.50, confidence "high".
- appears inNumbers that make the internet work
why?
Strength 0.50, confidence "high".
- appears inFilm and video frame-rate standards
why?
Strength 0.50, confidence "high".
Other connections
- contrasts with587
why?
Strength 0.50, confidence "high".
Religion & belief
25 December is Christmas Day, observed in Christian communities worldwide and as a public holiday in many countries; churches following the Julian calendar observe it on 7 January by the Gregorian reckoning. The date is a liturgical convention rather than a recorded birth date — the New Testament gives no date, and 25 December is first attested as the feast in fourth-century Rome. Churches that retain the Julian calendar, including several Orthodox churches, celebrate the same feast thirteen days later by Gregorian reckoning.
DocumentedReligion & beliefCulture: ChristianGeography: Christian communities worldwide and as a public holiday in many countries; churches following the Julian calendar observe it on 7 January by the Gregorian reckoning
Science
There are roughly 25 trillion red blood cells in an adult human body (adults). About 2.4 million are made every second, and each lasts around 120 days.
DocumentedScienceGeography: adultsThere are about 25 billion chickens alive at any moment. Figure as of 2023. Three for every person, and by a wide margin the most numerous bird on Earth. Their bones are proposed as a marker of the present geological epoch.
DocumentedScienceGeography: worldwide25 is the atomic number of manganese, a transition metal essential to steel production as an alloying agent and to human nutrition as a trace mineral.
DocumentedScience
Technology & computing
There are about 25 thousand international standards published by ISO. Figure as of 2024. Covering everything from screw threads to management systems. Almost none is legally binding on its own; standards acquire force when a contract or a regulation names one.
DocumentedTechnology & computingGeography: worldwidePort 25 is SMTP, the protocol that carries mail between servers. Its original design assumed a cooperative network and had no authentication at all, which is the root of email spam. Most consumer internet providers now block outbound port 25 entirely, routing users to authenticated submission ports instead.
DocumentedTechnology & computing
Culture
A 25th wedding anniversary is traditionally called a "silver" anniversary in the Western anniversary-naming convention.
Widely documentedCultureGeography: Western/English-speaking traditions
Law & regulation
Twenty-five is the minimum age the US Constitution sets for the House of Representatives, against 30 for the Senate and 35 for the presidency — seniority by chamber rather than three separately reasoned thresholds. It is also the age below which most car hire firms charge a young-driver surcharge or refuse hire.
DocumentedLaw & regulationGeography: United States
Common questions
Why is Christmas on 25 December?
The date is a liturgical convention, not a recorded birth date — the New Testament gives no date, and 25 December is first attested as the feast in fourth-century Rome. Churches still using the Julian calendar, including several Orthodox churches, keep the same feast on what is 7 January by Gregorian reckoning.
Is 25 a prime number?
No, 25 is not prime.
What are the factors of 25?
The factors of 25 are 1, 5, 25.
What is 25 in Roman numerals?
25 in Roman numerals is XXV.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 8 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026