You are walking a corridor in Hogwarts when you spot a tall wooden door framed by ten golden creature crests, with a dark panel in the middle that will not open. That is an Arithmancy Door, and it looks far scarier than it is. Every single one runs on the same bit of addition.
This guide covers how the puzzle works, the full creature cipher, worked solutions for the doors that are confirmed, and where to find the cheat sheet the game hides for you. There’s no wrong way to approach this, so take it at your own pace.
What Arithmancy Doors Are
Arithmancy Doors are puzzle doors spread around the inside of Hogwarts Castle. Each one shows two triangle equations on its panel, and beside the door sit two dials, one marked with a single question mark and one marked with two. Set both dials to the right creatures and the door swings open.
- Where they are: only inside the castle, in places like the Library Annex, the Central Hall, the Grand Staircase, the Astronomy Wing, the Great Hall and near Ravenclaw Tower.
- What you need: no spell and no tool. Just the creature values and a little arithmetic.
- Reward: each door leads to a small hidden room with a Collection Chest (often a Room of Requirement conjuration) plus a regular loot chest.
If you want to plan a route through the castle, our Hogwarts Legacy interactive map is handy for lining up Floo Flames before you start.
The Creature Cipher (0 to 9)
Each of the ten crests around the archway stands for a number. They are laid out in order: the crest at the bottom left of the frame is 0, and the values climb as you go up and around the arch until you reach 9 at the bottom right. So even if you forget a creature, the door itself is your cheat sheet.
| Number | Creature | Memory hook |
|---|---|---|
| 0 | Demiguise | Bottom left of the arch |
| 1 | Unicorn | One horn |
| 2 | Graphorn | Two horns |
| 3 | Runespoor | Three heads |
| 4 | Fwooper | The perched bird |
| 5 | Quintaped | Five legs, looks a bit like a crab |
| 6 | Salamander | The lizard |
| 7 | Grindylow | The squid shape with tentacles |
| 8 | Acromantula | Eight legs |
| 9 | Hydra | Bottom right of the arch |
Take Your Time: the most common slip is forgetting that the count starts at zero. If every answer you try feels one off, recount from the bottom left crest, which is 0, not 1.
How to Solve Any Arithmancy Door
Reveal the puzzle and look at the triangles. Each one has a big number in its center and a value at each of its three corners. Some corners show numbers, some show creatures, and one corner shows the question mark you need to solve.
- Convert creatures to numbers. Swap any creature corner for its value from the table above.
- Add the known corners. Add up the two corners you can read.
- Subtract from the center. The three corners always add up to the center number, so the center minus your sum is the missing value.
- Match the dial. The triangle with one question mark belongs to the single question mark dial. The triangle with two question marks belongs to the double question mark dial.
- Turn the dials. Rotate each one to the creature that matches your answer, and the door opens.
Worked Example: the 5 and 12 Door
Here is a real door, so you can see the method in action. The top triangle has a center of 5, with corners 0, 3 and the single question mark. The bottom triangle has a center of 12, with a Unicorn, a 4 and the double question mark.
- Top triangle: 0 + 3 = 3, and 5 minus 3 is 2. Set the single question mark dial to the Graphorn.
- Bottom triangle: the Unicorn is 1, so 1 + 4 = 5, and 12 minus 5 is 7. Set the double question mark dial to the Grindylow.
Confirmed Door Solutions
There are 12 Arithmancy doors in Hogwarts Castle in total. Doors are easiest to identify by the two center numbers on their panel, top first. Every answer below checks out against the math on the door itself.
| Center numbers | Where | Single ? dial | Double ?? dial |
|---|---|---|---|
| 9 and 4 | Library Annex, near the cheat sheet | Fwooper (4) | Runespoor (3) |
| 15 and 18 | Library Annex | Fwooper (4) | Quintaped (5) |
| 17 and 8 | Library Annex | Salamander (6) | Unicorn (1) |
| 21 and 17 | Central Hall | Acromantula (8) | Runespoor (3) |
| 5 and 12 | Astronomy Wing, near Charms | Graphorn (2) | Grindylow (7) |
For the doors on the Grand Staircase, near Ravenclaw Tower and in the Great Hall, run the five steps above on whatever numbers your panel shows. If you can’t find a question mark dial, turn around or check the floor above or below, and cast Revelio. Some dials sit out of sight, especially around the Central Hall door.
Where to Find the Cheat Sheet
Completionists, you’ll want to know: the game hides a torn Arithmancy study guide page that lists the creature values, and once you have it, you can reread it from your inventory any time.
- Fast travel to the Divination Classroom Floo Flame in the Library Annex.
- Head up into the wooden walkways above the classroom.
- Follow the walkway to the small area with a blackboard and an Arithmancy Door.
- Open the chest on the bench beside the blackboard to collect the page.
- Solve the door right next to it (the 9 and 4 door) as your warm up.
Lore Connection: Arithmancy is the Hogwarts elective about the magical properties of numbers, the same subject Hermione takes in the books. The doors turn that class into a lock, and the creatures on them are all beasts from the wider wizarding world.
Rewards and Why They Are Worth It
Every door opens onto a small treasure room with a Collection Chest that counts toward your collections, plus a chest that usually holds gear. Early on, a few free pieces of gear are a nice boost.
If you are only now picking the game up, our look at whether Hogwarts Legacy is still worth playing in 2026 covers how much of this side content there is. Plenty of people still play it on PC, and you can see how many on the live Hogwarts Legacy player count page.
Arithmancy Doors FAQ
How do you solve Arithmancy Doors in Hogwarts Legacy?
Convert the creatures to numbers, add the two known corners of each triangle, and subtract that from the center number. Set each question mark dial to the creature for the result.
What number is each creature on the Arithmancy Doors?
Demiguise 0, Unicorn 1, Graphorn 2, Runespoor 3, Fwooper 4, Quintaped 5, Salamander 6, Grindylow 7, Acromantula 8, Hydra 9. On the arch they run from bottom left to bottom right.
Where is the Arithmancy Door cheat sheet?
In a chest on a bench by a blackboard, in the walkways above the Divination Classroom Floo Flame in the Library Annex.
Do you need a spell to open Arithmancy Doors?
No. You only need to set the two dials beside the door to the correct creatures.
What is behind the Arithmancy Doors?
A small hidden room with chests, usually containing gear.
Checklist: grab the study guide page first, clear the 9 and 4 door next to it, then pick off the rest as you pass them. For more castle side content, start from our Hogwarts Legacy hub. It’s a marathon, not a sprint, and these doors are some of the most relaxing loot in the whole castle.
