To read a Roman numeral, you go letter by letter from left to right. There are two simple rules: when the values decrease you add, and when a smaller letter is before a bigger one you subtract.
The two-rule method
Decreasing values — add the values.
- VIII: 5 + 1 + 1 + 1 = 8
- XV: 10 + 5 = 15
- LXX: 50 + 10 + 10 = 70
A smaller before a bigger — subtract the small one from the big one, then continue.
- IV: 5 − 1 = 4
- IX: 10 − 1 = 9
- XL: 50 − 10 = 40
- XIV: 10 + (5 − 1) = 14
- XXIX: 10 + 10 + (10 − 1) = 29
The trick is to scan ahead one letter. If the next letter is bigger than the current one, you've found a subtractive pair — combine them before adding.
A step-by-step reading
Read LXXVIII.
Scan left to right:
L = 50.
X = 10. Next letter is X (same value, not bigger) → keep adding: 50 + 10 = 60.
X = 10. Next letter is V (smaller) → keep adding: 60 + 10 = 70.
V = 5. Next letter is I (smaller) → keep adding: 70 + 5 = 75.
I = 1. End: 75 + 1 = 76.
I = 1. End: 76 + 1 = 77.
Wait — I have one too many. Let me re-count the symbols. L X X V I I I — that's L + X + X + V + I + I + I. Compute: 50 + 10 + 10 + 5 + 1 + 1 + 1 = 78.
That's why slow, careful reading matters!
Reading with subtractive pairs
Read XCIV.
Scan left to right:
X = 10. Next letter is C (bigger!) → this is a subtractive pair: XC = 100 − 10 = 90.
I = 1. Next letter is V (bigger!) → IV = 5 − 1 = 4.
Add the parts: 90 + 4 = 94.
The whole numeral breaks into two pieces: XC + IV = 90 + 4 = 94.
A reading table for common values
Numeral
Value
Numeral
Value
I
1
XX
20
II
2
XXX
30
III
3
XL
40
IV
4
L
50
V
5
LX
60
VI
6
LXX
70
VII
7
LXXX
80
VIII
8
XC
90
IX
9
C
100
X
10
Notice the pattern: tens go X, XX, XXX, then XL (40, subtractive), then L, LX, LXX, LXXX, then XC (90, subtractive), then C.
Common mistakes when reading
Adding when you should subtract.IV is 4, not 6. The I comes before the V, not after.
Reading right to left. Always left to right.
Counting too many letters. III is 3, IIII is not standard (and would be 4 if it were).
