Concept 4 of 8
Roman Numbers: Letters That Count
Today's big idea
Add the letters left to right, but a smaller letter before a bigger one is taken away.
Seven letters cover every Roman number, and none may repeat more than three times.
How it works
👀 What's going on?
A film called Rocky II. A chapter numbered VII. A clock with XII at the top. Long ago in Rome nobody wrote 1, 2, 3, and their letters are still all over the things you look at.
💡 Here's the trick
Look at the two rules above. Seven letters do all the work. I is 1, V is 5 and X is 10, then L is 50, C is 100, D is 500 and M is 1000. Read left to right and add as you go. Position is the twist: a smaller letter after a bigger one is added, but a smaller letter before a bigger one is taken away.
🪄 How to do it
- 1.Read the letters left to right, the way the pairs above are read.
- 2.Add each letter's value as you go.
- 3.If a smaller letter sits just before a bigger one, take it away instead.
✍️ Try it
Read XVIII. Then read XXIX.
XVIII is X for 10, V for 5, then three Is, which makes 18. XXIX opens with XX for 20, and then IX puts the small I before the X, so that pair is 9. Together they make 29.
⚠️ Watch out
You might be thinking you can just repeat a letter until you reach the number you want. Four Is in a row is not allowed, which is why 4 is written IV and never IIII. No letter may appear more than three times in a row, and that rule is the whole reason the take-away trick exists.
🌟 Why this matters
Clock faces, book chapters, film sequels and the names of kings and queens all still use these letters. Learn seven of them and you can read numbers written two thousand years ago.
Exam tip: Roman questions are pure recall, so they are among the quickest marks on any paper.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“What number is XXVI?”
- 1
Break into letters
X, X, V, I — that's 10, 10, 5, 1. 🏛️
- 2
Check each letter's order
Every smaller letter is after a bigger or equal one → just add.
- 3
Add them up
10 + 10 + 5 + 1 = 26
- 4
Decoded ✓
XXVI = 26
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
I = 1, V = 5, X = 10, L = 50. Smaller AFTER bigger → add. Smaller BEFORE bigger → subtract.
ROMAN · ROUND 1 OF 3
XIV
Decode this Roman number
Type the Arabic number for XIV.
Quick check
✅ VERIFICATION
What is the Roman numeral for 14?
⚡ Finish the activity above first to answer.
Keep going!
Up next: Number Line-Up
Compare digits left-to-right to order numbers.