How to Read Roman Numbers

Hi!

So just like me, your interested in learning roman numerals are you? Let’s dive in!

(Note: Roman numerals are for writing down “small” positive numbers, so not for doing math or for keeping track of the number of cells in the human body. Think numbers big enough for counting entrances to the coliseum, people in a village, or the size of armies.)

First off, I means 1, II means 2, and III means 3. So you simply repeat the same I one, two, or three times.

However, 4 and upward works differently, because you’re not allowed to repeat a roman numeral more than 3 times. To solve this, we need the next numeral, which is V for 5. So now we have:

• I for 1
• II for 2
• III for 3
• V for 5

To write 4, we need to subtract 1 from 5 by writing I before V, like this: IV.

We can now write the numbers 1 through 5.

To write 6, we add 1 to 5 by writing an I after the V, like this: VI.

To write 7, we add 1 twice: VII.

And the same for 8: VIII.

For 9, we’re stuck again for the same reason as with 4, we’re not allowed to repeat the I more than 3 times, so we need the next numeral, which is X for 10.

9 is 1 subtracted from 10, namely IX. And 10 is X, like I just said.

Now we’ve got:

• I for 1
• II for 2
• III for 3
• IV for 4
• V for 5
• VI for 6
• VII for 7
• VIII for 8
• IX for 9
• X for 10

We’ve also learned a few rules. Try your skills with the questions below! Try to think of the answer, then click to reveal it to see if you remembered correctly. If you need more info, re-read the text above.

Now, let’s continue with 11 using the same rules, it’s 1 added to 10, namely XI.

12 and 13 follow the same pattern, XII and XIII.

15 is 5 added to 10, so you write V (5) after the X (10), giving you XV.

14 works the same, except you are only adding 4, which is 1 subtracted from 5, IV, so we get XIV.

We just found a new rule! The I in 14 is subtracting from the V (5) and not from the whole 15, so not IXV, which is illegal: you subtract from the right-most possible numeral.

Another subtraction rule: you cannot repeat subtractions, so IIX for 8 is illegal, add 3 to 5 instead by writing VIII (as we covered above).

Ok, so thus far we’ve got 1 through 15. Let’s review with some questions! Again, try to think of the answer before you click to reveal the correct one. Re-read above as needed.

Now onto 20! You are allowed to repeat X too, so 20 is simply XX!

What’s more, 11 through 20 is just 1 through 10 with an X in front:

• XI for 11
• XII for 12
• XIII for 13
• XIV for 14
• XV for 15
• XVI for 16
• XVII for 17
• XVIII for 18
• XIX for 19
• XX for 20

The same goes for 21 through 30, XXI for 21, XXII for 22, …, XXIX for 29, and XXX for 30.

Sneak question!

We can now write up to 39 by putting XXX in front to write for example 36 (XXXVI).

Ok, so with XXX for 30 we’ve repeated X 3 times, so we need a new symbol to go above 39, and L for 50 comes to the rescue!

With this, we can use XL to write 40 (50 minus 10) and for example XLIII for 43.

Continue and add 10 to 50 by writing LX for 60, LXX for 70, and LXXX for 80.

The “can’t repeat a symbol more than 3 times” rule now forces us to invent yet another numeral, so we use C for 100 (think cent or century for 100).

We can now write not only up to 100, but also up to 200 by writing CC, or 190 by subtracting 10 from the right-most C, giving us CXC. We can even write 199 by adding 9 to that: CXCIX. Add one or two more Cs in front to write 299 (CCXCIX) or 399 (CCCXCIX).

We need a new symbol for 500, and D comes to the rescue and gives us 501 (DI), 450 (CDL) and 521 (DXXI).

This leads us to the last symbol.

Drumroll!

M is 1000!

To remember that M is 1000, think millisecond (for 1 thousandth of a second) or mille for 1000 in French or Italian or mil in Spanish (I’m sorry if that doesn’t help at all…)

Anyway, we can now write numbers from 1 (I) up to 3999 (MMMCMXCIX).

You probably won’t run into numbers at 4000 and above, but these can be written using a dash above a numeral to indicate “times a thousand”, so V̅ becomes 5000, L̅ 50 000, and M̅ 1 000 000. This allow us to write 4837 (MV̅DCCCXXXVII) or 2 000 192 (M̅M̅CXCII).

(Another way to write 1000 is CIↃ, and here each added C and Ↄ multiplies by 10, so CCIↃↃ is 10 000. In the same system, IↃ is 500 and IↃↃ is 5000 and so on.)

This leads us to an important point: the Romans had multiple rules over the years and also broke them when they felt like it. This is why many clocks say IIII for 4 (clocks predate the switch to IV) and why the 44th gate at the Coliseum is XLIIII.

Time for some more questions!

Now we’ve just got some minor details left and you’ll be an expert!

XCIX is 99, but why not just IC to indicate 100 minus 1? Because you are not allowed to subtract using a symbol that’s more than two steps smaller. So for C, that leaves us with L or X.

Another rule is: you can only subtract using I, X, or C.

With the above two rules, the only legal way to write 99 is XC for 90 plus IX for 9, giving us XCIX.

Questions!

Our last rule: V, L, and D are never repeated. So no VV foe 10 (use X) or DDD for 1500 (use MD).

Tada!

Now you’re a Roman Numeral expert! Congrats!

🎉

Do you want to learn more things like this?

Including periodic reminders of old information you’ve read, akin to the questions above?

Then subscribe to my newsletter!