397 in Roman numerals

How CCCXCVII is built

Roman numerals are written one decimal place at a time, largest first.

1. CCChundreds · 3C written 3 times: 3 × 100 = 300.
2. XCtens · 9X before C means 100 − 10 = 90. This saves writing LXXXX.
3. VIIones · 7V (5) plus II (2) makes 7.

300 + 90 + 7 = 397

The pair XC uses subtraction: a smaller letter before a larger one is taken away from it. Only six pairs work this way: IV, IX, XL, XC, CD and CM. More on subtraction

Mistakes to avoid

• Not CCCLXXXXVII (11 letters). That adds everything up without subtraction. The Romans sometimes wrote numbers this way, and clocks still show 4 as IIII, but today CCCXCVII (8 letters) is the standard.