POISSON
ThePOISSON
function returns the Poisson distribution probability density function, which is used to show the probability of a certain number of events occurring in a fixed interval of time or space. It takes in the values for the number of events (x), the mean (mean), and a boolean for whether or not to return the cumulative distribution (cumulative).
 How to use
POISSON
formula?  Examples of using
POISSON
formula POISSON
formula not working? Similar formulas to
POISSON
Usage
Use the POISSON
formula with the syntax shown below, it has 2 required parameters and 1 optional parameter:
 x (required):
The number of events to evaluate the probability for.  mean (required):
The mean number of events that occur in the given interval.  cumulative (optional):
A boolean that determines whether to return the cumulative distribution function or probability density function. If omitted or false, it will return the probability density function.
Examples
Here are a few example use cases that explain how to use thePOISSON
formula in Google Sheets.
Estimating the probability of an event
Suppose that you know that a certain number of events occur every day on average, and you want to know the probability of a certain number of events occurring in a day. You can use the POISSON
function to calculate this probability.
Analyzing traffic congestion
You can use the POISSON
function to analyze traffic congestion in a particular area. By estimating the average number of vehicles that pass through the area in a given time interval, you can use the function to estimate the probabilities of different levels of congestion.
Modeling radioactive decay
The POISSON
function is also used in nuclear physics to model the probability of radioactive decay events occurring in a given time interval.
Common Mistakes
POISSON
not working? Here are some common mistakes people make when using the POISSON
Google Sheets Formula:
Using a negative value for x
The POISSON
function requires that the value of x
be a nonnegative integer. If a negative value is used, the function will return an error.
Using a negative value for mean
The POISSON
function requires that the value of mean
be a positive number. If a negative value is used, the function will return an error.
Forgetting to set the cumulative argument
The POISSON
function requires that the cumulative
argument be set to either TRUE
or FALSE
. If this argument is omitted or misspelled, the function will return an error.
Related Formulas
The following functions are similar to POISSON
or are often used with it in a formula:

BINOM.DIST
The
BINOM.DIST
function returns the probability of a certain number of successes in a fixed number of trials given a probability of success in each trial. It is most commonly used in statistical analysis and hypothesis testing. The function can calculate either the probability mass function (PMF) or the cumulative distribution function (CDF) depending on the value of thecumulative
parameter. 
NORM.DIST
The
NORM.DIST
formula is a statistical function that returns the normal distribution of a specified variable. It is used to determine the probability of a random variable falling within a specified range of values. This function is commonly used in finance and scientific research. 
EXPON.DIST
The EXPON.DIST function returns the exponential distribution of a specified random variable, x, given a specified lambda, LAMBDA. The exponential distribution is commonly used to model the time between events in a Poisson process. The function returns the probability density function or the cumulative distribution function of the exponential distribution depending on whether the cumulative argument is set to TRUE or FALSE. This function is useful for analyzing reliability data and can be used to determine the probability that a component will fail before a certain time.
Learn More
You can learn more about the POISSON
Google Sheets function on Google Support.