Probability Calculator
Calculate single and combined event probabilities.
- 100% free
- Private in browser
- No signup
- No watermarks
Probabilities
- P(A)
- 16.67%
- P(B)
- 50%
- P(not A)
- 83.33%
- P(A and B)
- 8.33%
- P(A or B)
- 58.33%
Rate this tool
Be the first to rate — helps others and improves this page.
About Probability Calculator
Probability tells you how likely an outcome is, on a scale from 0 to 1. Probability Calculator on TheToolss computes the probability of two events from their favorable and total outcomes, then combines them: the chance both happen (A and B), either happens (A or B), and the complement (not A). It assumes the two events are independent. It is ideal for statistics homework and quick odds checks. It runs in your browser — free, private, and no signup.
How to use Probability Calculator
- Enter favorable and total outcomes for event A.
- Enter favorable and total outcomes for event B.
- Read the individual and combined probabilities.
Key features
- Single-event probability
- P(A and B) and P(A or B)
- Complement P(not A)
- Results as decimals (0–1)
- Private in-browser calculation
Frequently asked questions
- Is the Probability Calculator free?
- Yes. It is free on TheToolss with no signup.
- How is single-event probability found?
- Probability = favorable outcomes ÷ total possible outcomes, giving a value between 0 and 1.
- Does it assume independence?
- Yes. The combined formulas assume A and B are independent events. For dependent events the math differs.
- How do I read the result?
- A value of 0 means impossible, 1 means certain, and 0.5 means a 50% chance. Multiply by 100 for a percentage.
- Is my data uploaded?
- No. The calculation runs in your browser.
Related In-Depth Guides
Learn practical workflows, real-world examples, and expert tips in our comprehensive guides:
Home Remodeling Material Takeoff Guide: Tile Grout, Drywall Mud & Kitchen Cabinet Runs
Professional contractor takeoff formulas for interior renovations. Accurately estimate tile grout bags, drywall joint compound for Level 4 finishes, and modular kitchen cabinet spacing.
How to Size a Home Emergency Generator: Running vs Surge Watts & Propane Runtime
Complete electrical guide to calculating running watts, motor startup surge wattage, transfer switches, and fuel consumption for winter storms and outages.
Patio Paver & Retaining Wall Installation Guide: Base Gravel, Sand & Block Calculations
Avoid settling, cracking, and water pooling. Step-by-step math for paver patterns, 4-6 inch aggregate base, 1-inch bedding sand, and drainage gravel.