Geometric Distribution Calculator

Geometric distribution describes the number of failures before one success. For example, you may be throwing a die until you get a result of 6. Geometric distribution lets you determine the probability of getting a six at the first throw, the second, etc.

One of the properties of geometric distribution is memorylessness. It means that the probability distribution of the upcoming results does not depend on how many failures you already got. The exponential distribution has the same property. Visit the exponential distribution calculator if you want to learn more about it.

Some examples of geometric distribution include:

• Throwing a die multiple times to get a result of 6;
• A couple that plans to have multiple children until the first boy;
• Transmission of a sequence of bits until the first error; and
• Interviewing voters until you find someone who voted for the same candidate as you did.

The formula for geometric distribution is

P = (1-p)^x * p

where:

• x is the number of failures before the first success;
• p is the probability of achieving a success in one trial; and
• P is the geometric probability of getting a success after x failures.

You can also use our geometric distribution calculator to find the following values:

• Mean (the expected value) is equal to μ = (1-p)/p
• Variance is equal to σ² = (1-p)/p²
• Standard deviation is equal to σ = √[(1-p)/p²]

Let's analyze the example with die throwing. You are throwing a die until getting the result of six. What are the chances that you will get a six on your second throw?

Don't have a die? No problem, just use the dice roller calculator!

1. Determine the probability of success for one trial. For a die, it is equal to 1/6.

2. Calculate how many failures you will have before a success. For a successful second throw, only one throw will be a failure.

3. Calculate the geometric probability with the help of the equation above:

   P = (1-p)^x * p

   P = (1-1/6)¹ * 1/6 = 0.1389 = 13.89%

4. You can also calculate the expected number of throws needed before you get a success, the variance, and standard deviation. Make sure to check the results with the geometric distribution calculator!