Probability Calculators
Crunch the numbers on your game's dice rolls and card draws before you ever sit down to playtest.
On This Page
Overview & Why It Matters
The Probability Calculators help you understand the statistical backbone of your game mechanics before playtesting. Instead of discovering a mechanic feels terrible after 10 play sessions, you can calculate upfront that a player has only a 4% chance of succeeding — and adjust accordingly.
Dice Pool
Mix different standard dice and model any pool
Card Draw
Calculate odds of drawing specific cards from a deck
Custom Dice
Analyze image-face dice from your actual game components
Access: All three calculators are available in Calculators in the navigation menu. Your last 10 calculations are saved automatically so you can reference them later.
Dice Pool Calculator
Build any combination of polyhedral dice and instantly get probability breakdowns.
Step 1 — Build Your Dice Pool
Click the quick-add buttons to add dice types to your pool:
- Use the +/− buttons or type a number to set how many of each die to roll
- dCustom — enter comma-separated face values (e.g.
1,1,2,3,5,8) - Fudge — pre-loaded with
-1,-1,0,0,1,1(standard FATE/Fudge die) - Add as many different die types as needed — the pool summary shows your total count
Step 2 — Choose What to Calculate
Average & Range
Shows the minimum possible roll, maximum possible roll, and the statistical average. Useful for calibrating game balance — know what "typical" looks like.
Hit a Specific Total (Target Number)
Enter a target value (e.g. 15). The calculator shows the probability of rolling at least that total. Includes a full distribution chart showing the odds of every possible result.
Count Successes (X or Higher)
Set a success threshold (e.g. "4 or higher counts"). The calculator shows the expected number of successes and a hit-distribution breakdown per die type — perfect for dice-pool combat systems.
What the Results Show
- Big percentage / average: The headline probability or average roll
- Rating badge: Very Likely / Good Odds / Coin Flip Territory / Long Shot — a quick gut-check label
- Pool breakdown: When rolling multiple die types, each type's individual contribution is shown as a bar
- Distribution chart: Every possible total and its exact probability (shown when ≤ 50 distinct outcomes)
- Plain-English explanation: A sentence describing what the numbers mean in context
Card Draw Calculator
Uses hypergeometric probability — the mathematically correct model for drawing cards from a finite deck without replacement.
Inputs Explained
Total number of cards in the deck (e.g. 54 for a standard game deck)
How many copies of the card you're hoping to draw exist in the deck (e.g. 4 copies of "Gold Mine")
How many cards you draw (e.g. your opening hand of 7 cards)
At least one — any copy in hand. Exactly N — a precise number. At least N — N or more copies.
Common Design Questions This Answers
- "If I put 3 copies of my key combo card in a 40-card deck, what are the odds of having it in my opening hand of 5?"
- "Is my starting resource card frequent enough at 8 copies in 54?"
- "Will players reliably see this mechanic by the midgame?"
Project shortcut: If you've added card components to a project, use the project picker to load your decks. Click a deck name, then a specific card, and the calculator pre-fills the deck size and copies for you.
Custom Dice Calculator
Analyze dice that use custom image faces (like action dice, symbol dice, or faction-specific dice). This calculator is tied directly to your project's custom dice components.
How It Works
- Select your project from the project picker (top of the page)
- Your custom dice appear — click a die to add it to the pool and set quantity
- Click any face image from your die to set it as the target face
- Choose your success mode: at least one, exactly N, or at least N
- Hit "Calculate" — the system counts which die faces match the target and computes exact odds
Results Breakdown
- Target face image — confirms which face you're targeting
- Overall probability — odds of hitting your success condition
- Expected hits — average number of successes across the whole pool
- Per-die-type breakdown — shows each custom die's individual hit rate (e.g. "Sword Die: 2/6 sides → 33%")
- Hit distribution chart — probability of getting 0, 1, 2… N successes
Prerequisite: Custom dice must be added to your project with face images uploaded. See the Component System guide for instructions on creating custom dice.
Project Integration
The calculators are aware of your projects. The project picker at the top of the calculators page lets you load your real game data directly:
Dice Quick-Pick
Your project's dice components appear as buttons. Click one to add it to the pool with its configured quantity. Works for both standard and custom dice.
Deck Quick-Pick
Your decks are listed with total card counts. Click a deck to see individual cards. Click a card to auto-fill the deck size and copy count into the card draw calculator.
Calculations are saved per project: When you run a calculation with a project selected, it's saved to that project's history so you can track balance changes over time.
Calculation History
Your last 10 calculations are automatically saved and shown on the right side of the calculator page. Each entry shows:
- The type of calculation (dice, cards, or custom dice)
- A summary of the inputs used
- The headline result
- Which project it was associated with (if any)
- When it was calculated
History is per-user. Calculations are automatically replaced once you exceed 10 entries (oldest removed first).
Reading the Results
Rating Badges — What They Mean
Distribution Charts
The horizontal bar chart shows every possible outcome. The width of the bar represents the percentage chance of that exact result. Wide bars = more likely. Narrow bars = rare outcomes. Use this to identify if your distribution has a "sweet spot" (a cluster of likely outcomes) or if results are too spread out.
Practical Examples
Example 1: Calibrating Combat Difficulty
You want players to roll 2d6 and need an 8 or higher to succeed. Is that too hard?
Pool: 2× d6 | Mode: Target Total | Target: 8
Result: ~42% chance — Coin Flip Territory
That's a fair challenge. Drop to 7 and you hit 58% (Good Odds).
Example 2: Opening Hand Consistency
Your 54-card deck has 4 copies of a key "Setup" card. Will players see it in their opening hand of 7?
Deck: 54 | Target cards: 4 | Draw: 7 | Mode: At least one
Result: ~40% — Coin Flip Territory
If that card is critical, add more copies. With 6 copies: ~57% (Good Odds).
Example 3: Custom Action Die Success Rate
Your d6 action die has 2 "Attack" faces, 2 "Move" faces, 1 "Defend", 1 "Wild". Rolling 3 dice — how often do you get at least one Attack?
Custom die: 2/6 Attack faces | Pool: 3 dice | Mode: At least one
Result: ~70% — Good Odds
Feels fair. Players can usually attack but not always.