Roman Numerals Converter

Seven letters, and two rules

I is 1, V is 5, X is 10, L is 50, C is 100, D is 500, M is 1,000.

1. Letters are added when written largest first. MMXXVI is 1000 + 1000 + 10 + 10 + 5 + 1 = 2026.
2. A smaller letter before a larger one is subtracted. IV is 4, IX is 9, XL is 40, CM is 900.

Subtractive notation has its own restrictions, which is why some plausible-looking numerals are wrong. Only I, X and C subtract, and each only from the next two values up: I from V and X, X from L and C, C from D and M. So 99 is XCIX, not IC.

The tool above accepts a loose numeral and tells you the standard form.

There is no zero, and that is the problem

The system has no symbol for nothing, because it was built for counting and recording rather than calculating. That sounds like a small gap and it is not.

Without zero there is no place value, and without place value there is no column arithmetic. Try multiplying XLVII by XIX on paper. Roman merchants used a counting board for arithmetic and wrote the numerals down only to record the result.

The Hindu-Arabic system that replaced it carried both innovations together, and the shift took centuries — Fibonacci was still arguing for it in 1202, and some cities banned the new numerals on the grounds they were easier to forge.

The limit is 3,999

With only M for a thousand, you would need four Ms for 4,000, which breaks the rule against four identical letters. Classical systems used an overline — a bar over a numeral multiplied it by a thousand — but there is no single standard, so most converters stop at MMMCMXCIX.

Where they survive

• Clock faces, often with IIII rather than IV for visual balance against VIII.
• Film copyright dates, historically to make the year less obvious to audiences.
• Monarchs and popes — Elizabeth II.
• Book prefaces, numbered separately from the main text.
• The Super Bowl, which famously skipped the numeral for the fiftieth.

Common uses

• Reading a date on a building or in film credits.
• Writing a year for a certificate or inscription.
• Homework.
• Checking a tattoo before it is permanent, which is a more common use than you might think.

Questions people ask

How do Roman numerals work?

Letters add when written largest first, and a smaller letter before a larger one is subtracted. MMXXVI is 2026; IV is 4.

Why is there no zero?

Because the system was built for recording rather than calculating. Without zero there is no place value, and without place value no column arithmetic.

What is the largest Roman numeral?

MMMCMXCIX, 3,999. Beyond that you would need four Ms, which breaks the rules; classical systems used an overline instead.

Why is 99 XCIX and not IC?

Because only I, X and C can subtract, and only from the next two values up. I cannot be taken from C.

Why do clocks show IIII instead of IV?

Visual balance — IIII sits opposite VIII and looks more even. The practice is centuries old and has several competing explanations.

Built into the page

The whole chart is part of the page, so it works with no connection and nothing is requested while you use it.