Two lookup tables that come up in math, science, and history classes: what each Roman numeral is
worth, and the full Greek alphabet with the jobs its letters do in formulas.
Roman Numeral Values
Numeral
Value
I
1
V
5
X
10
L
50
C
100
D
500
M
1,000
How Roman Numerals Combine
Read left to right, and add a numeral that is equal to or smaller than the one before it:
VI = 5 + 1 = 6, and XXI = 10 + 10 + 1 = 21.
A smaller numeral placed before a larger one is subtracted. Only six pairs work this way:
IV (4), IX (9), XL (40), XC (90), CD (400), and CM (900).
Don’t repeat a numeral more than three times in a row: 4 is IV, not IIII.
Number
Numeral
How it breaks down
14
XIV
10 + 4
42
XLII
40 + 2
99
XCIX
90 + 9
444
CDXLIV
400 + 40 + 4
1999
MCMXCIX
1000 + 900 + 90 + 9
2026
MMXXVI
1000 + 1000 + 20 + 6
The Greek Alphabet
Letter
Name
Where you’ll see it
Α α
Alpha
Angles; the significance level in statistics
Β β
Beta
Angles; beta particles; regression coefficients
Γ γ
Gamma
Gamma rays; the gamma function
Δ δ
Delta
”Change in” (Δx); a small change (δ)
Ε ε
Epsilon
A very small quantity; permittivity
Ζ ζ
Zeta
The Riemann zeta function
Η η
Eta
Efficiency; viscosity
Θ θ
Theta
An angle
Ι ι
Iota
Rarely used in formulas
Κ κ
Kappa
Curvature; thermal conductivity
Λ λ
Lambda
Wavelength; eigenvalues
Μ μ
Mu
The mean; micro- (one millionth); friction coefficient
Ν ν
Nu
Frequency
Ξ ξ
Xi
A random variable or coordinate
Ο ο
Omicron
Rarely used in formulas
Π π
Pi
π≈3.14159; capital Π means “product of”
Ρ ρ
Rho
Density; correlation
Σ σ
Sigma
Capital Σ means “sum of”; lowercase is standard deviation
The standard rule is never to repeat a numeral more than three times, so 4 uses subtraction: one before five. You may still see IIII on clock faces, which is a design tradition, not an error.
How do I read a year like MCMXCIX?
Split it into chunks: M (1000) + CM (900) + XC (90) + IX (9) = 1999. Any pair where a smaller numeral comes first is one chunk that subtracts.
Is there a Roman numeral for zero?
No. The Roman system had no symbol for zero, and there are no negative numerals either. Standard numerals also top out at 3,999 (MMMCMXCIX).
Why do some Greek letters have two common uses?
Each field reuses the letters independently, so the same letter can mean different things in physics and statistics. The subject and the formula around it tell you which meaning applies.