How to Write Roman Numerals
Learn the simple rules step by step!
The 7 Roman Letters
Roman numerals use only 7 letters. Each letter has a number value:
The Roman numeral system is built on seven fundamental symbols, each representing a specific value. These symbols form the building blocks for all Roman numerals, and understanding their values is essential for reading and writing Roman numerals correctly.
- •There are exactly 7 symbols in the Roman numeral system
- •Each symbol represents a specific, fixed value
- •The symbols follow a pattern: I(1), V(5), X(10), L(50), C(100), D(500), M(1000)
- •Notice the pattern: 1, 5, 10, 50, 100, 500, 1000 - alternating between powers of 10 and intermediate values
- •These symbols can be combined using specific rules to create any number
- •All Roman numerals are built from combinations of these 7 letters only
Rule 1: Adding Numbers
When a small letter comes AFTER a big letter, you ADD them together.
Addition is the fundamental principle of Roman numerals. When letters are arranged from largest to smallest (left to right), or when smaller letters follow larger ones, you simply add their values together.
- +Letters are generally written in descending order of value (largest first)
- +When a smaller letter follows a larger letter, add their values
- +Multiple letters of the same value placed together are added (II = 1+1 = 2)
- +This is the most common way Roman numerals work
- +Always read from left to right, adding values as you go
Let's Break Down VI Step by Step!
Because I comes AFTER V, we add: 5 + 1 = 6
Rule 2: Taking Away Numbers
When a small letter comes BEFORE a big letter, you SUBTRACT (take away) the small number.
Subtraction in Roman numerals follows strict rules to avoid confusion. Only three letters can be used for subtraction: I, X, and C. Each can only subtract from specific letters.
- −I can only subtract from V and X (making IV=4 and IX=9)
- −X can only subtract from L and C (making XL=40 and XC=90)
- −C can only subtract from D and M (making CD=400 and CM=900)
- −V, L, and D can NEVER be used for subtraction
- −Only one letter can be subtracted at a time (never II, XX, or CC before another letter)
- −You cannot subtract across multiple powers of ten (like IC for 99 - use XCIX instead)
- −These are the only 6 valid subtractive combinations in standard Roman numerals
Let's Break Down IV Step by Step!
Because I comes BEFORE V, we subtract: 5 - 1 = 4
Only I, X, and C can be used to subtract. They can only subtract from certain letters.
Rule 3: Repeating Letters
You can write the same letter up to 3 times in a row to add more value.
Repetition allows you to create numbers by repeating the same Roman numeral letter up to three times. This rule has important limitations that prevent confusion and maintain readability.
- ×Only I, X, C, and M can be repeated
- ×Letters can be repeated a maximum of 3 times in a row
- ×V, L, and D are NEVER repeated (they represent "intermediate" values)
- ×Instead of repeating V, L, or D, use the next higher letter (VV becomes X, LL becomes C, DD becomes M)
- ×Repetition follows the addition rule - you add the repeated values together
- ×Four consecutive identical letters are avoided in modern notation (use IV instead of IIII)
V, L, and D are NEVER repeated. Instead we use X, C, and M.
Rule 4: Writing Order
Write the biggest numbers first, then smaller ones. Go from left to right.
Roman numerals follow a strict left-to-right order principle. This ordering system ensures that numbers are written consistently and can be read correctly by following the addition and subtraction rules.
- →Always write numerals in descending order of value (largest to smallest)
- →Start with the largest denomination and work down to the smallest
- →Subtractive combinations (like IV, IX, XL) are treated as single units in the ordering
- →The ordering applies to the overall structure, not individual letters within subtractive pairs
- →When combining different denominations, place thousands first, then hundreds, then tens, then units
- →Never place a larger numeral after a smaller one unless using subtraction rules
All Rules Working Together!
This example shows ALL THREE rules working together. Let's Break Down XLIII Step by Step!
Rule 2: Subtraction
X comes BEFORE L, so we subtract
Rule 3: Repetition
Same letter repeated 3 times
Rule 1: Addition
Combine the parts together
Step-by-Step Breakdown
Step-by-Step Breakdown:
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Step-by-Step Breakdown:
Common Mistakes to Avoid
Learn from these common errors!
Memory Tips
Start with the largest values and work your way down
Remember that only I, X, and C can be used for subtraction
Never repeat V, L, or D - they represent intermediate values
There are only 6 valid subtractive combinations: IV, IX, XL, XC, CD, CM
When in doubt, use addition rather than subtraction
Practice with years and dates to build familiarity
Practice Exercises
Test your understanding with these examples:
Ready to Practice More?
Now that you know the rules, it's time to practice! Try our interactive tools to become a Roman numeral expert.