A weathered stone lintel carved with Roman numerals, lit by low afternoon sun, with plain sky to one side
AI-generated image, not a photograph of a real person or place.
romans9

HOW THE OLD NUMBERS WORK

One before ten:
that's IX.

IX ten take away one

  • Big to small, add
  • Small before big, subtract
  • No zero at all
  • Two rules, seven letters

Seven letters write every Roman numeral.

I, V, X, L, C, D and M are all you need. Line them up from biggest to smallest and add; put a small one in front of a bigger one and subtract. That is why IX means 9, and why so many clock faces quietly break the rule at four.

Updated

Read a numeral

THE SHORT ANSWER

Add, mostly.
Sometimes subtract.

Roman numerals have no place value and no zero.
Each letter keeps its own value wherever it sits.

THE LETTERS

Seven symbols

I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1,000. XXVII is 10 + 10 + 5 + 1 + 1 = 27.

Read a numeral

SUBTRACTION

Why IX is 9

A smaller symbol in front of a larger one is taken away: IV is 4, IX is 9. The same trick gives XL (40), XC (90), CD (400) and CM (900).

See the numbers

STILL IN USE

Clocks, kings and years

You still meet them on clock faces, on dates carved into buildings, and in the regnal numbers of monarchs, such as Henry VIII.

Spot them yourself

A QUICK READING CHECK

What does this
numeral say?

Pick a numeral to see its value and the rule that unlocks it. The bar shows how many symbols it takes to write.

Numeral check

Choose a numeral
IX9

I before X means ten take away one. Two symbols, one subtraction.

IIII on a clock4

The older additive way of writing four. Many clock faces use IIII at four o'clock but IX at nine, a habit going back to very early clocks.

XLIIII44

Seen on the numbered gates of the Colosseum: XL (40) uses subtraction, but IIII (4) does not. Romans mixed the two styles in one number.

MCMXII1912

M (1,000) + CM (900) + X (10) + II (2). Read it in chunks from the left, one decimal place at a time.

MMXXVI2026

MM (2,000) + XX (20) + VI (6). Years in this century start with MM.

Sources: Roman numerals reference article (Wikipedia) for the rules, the Colosseum gate and the year examples; Seiko Museum Ginza on IIII on clock dials.

Examples from the Roman numerals reference article and the Seiko Museum Ginza. A history and maths explainer only.

TWO NUMBERS WORTH KNOWING

A small alphabet
with a ceiling.

How few letters the system needs,
and how far the standard form can count.

7 letters

Letters used in modern Roman numerals

The modern style uses only I, V, X, L, C, D and M, each with a fixed value, so the same letter means the same amount wherever it appears.

SYMBOLS · STANDARD FORM

3,999 MMMCMXCIX

Largest number in the standard form

Written the usual way, the biggest number is MMMCMXCIX. Romans and later writers used other devices, such as bars and brackets, for larger numbers.

LIMIT · STANDARD FORM

There has never been one official standard for Roman numerals: usage varied in ancient Rome and became very mixed in the Middle Ages. From the 14th century they were gradually replaced by the Hindu-Arabic digits we use now.

FOUR PLACES TO LOOK

Old numbers,
everyday places.

A foundation stone on a brick building with a year carved in Roman numerals, ivy at its edge
AI-generated image, not a photograph of a real person or place.

Once you know the two rules, you will notice Roman numerals all around you. Try reading these next time you pass one.

  1. A clock face

    Check four o'clock. Is it IIII or IV? The clock of Elizabeth Tower at Westminster uses IV; many others use IIII.

  2. A building's date stone

    Years are often carved in Roman numerals. Break the number into thousands, hundreds, tens and units.

  3. A monarch's name

    Regnal numbers such as II or VIII are read as ordinals: "the second", "the eighth".

  4. The end of a film or programme

    Copyright years on title screens are often in Roman numerals, such as MMXXVI for 2026.

THE IIII PUZZLE

Why four o'clock
breaks the rule.

A close view of the top of an old clock face with the Roman numerals X, XI and XII
AI-generated image, not a photograph of a real person or place.

The Seiko Museum Ginza notes that IIII was the usual way to write four in medieval Europe until around the 17th century, and appears on turret clocks made before then. Wells Cathedral's clock, from about 1390, is an early English example.

Several stories try to explain why it stuck, including one about a French king. The museum says the most popular explanation is simply that IIII looks better balanced against VIII on a round dial.

Questions

Questions people ask

Why is 9 written IX and not VIIII?

Putting a smaller symbol before a larger one means subtract, so IX is 10 minus 1. VIIII was also used in the past, but less often, and IX is the standard form today.

Why do some clocks show IIII instead of IV?

IIII was the usual medieval way to write four and survives on many clock dials. The Seiko Museum Ginza says the most popular explanation is that it looks better balanced against VIII.

Is there a Roman numeral for zero?

No. The system has no zero symbol and no place value. The Latin word nulla, meaning none, was later used for zero, with the earliest attested uses being medieval.

What is the biggest number you can write?

In the standard form the largest is 3,999, written MMMCMXCIX. Other methods, such as bars and brackets, were used for larger numbers.

Do children still learn Roman numerals in England?

Yes. The national curriculum for maths includes reading Roman numerals on clocks, to 100 in Year 4 and to 1,000 in Year 5, with years written in Roman numerals.

Sources

Where the facts come from

  1. Wikipedia: Roman numerals (rules, history and modern uses)
  2. The Seiko Museum Ginza: why 4 is written IIII on clock dials
  3. Science Museum blog: the Wells Cathedral clock mechanism re-displayed
  4. Association of English Cathedrals: the astronomical clock at Wells Cathedral
  5. GOV.UK: National curriculum in England, mathematics programmes of study

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