# Rule action: Calculate list length

Used for: calculating how many elements a list has.

Used in: “THEN”-statements and “ELSE”-statements.

## Calculate list length

The "calculate list length" rule determines the number of elements in a list. This is particularly useful when you have all the available sizes of a product in a list and need to calculate the total number of sizes available.

For instance, if you have a list of sizes for a product, you can use this rule to determine how many sizes are available. The example rule in the screenshot below illustrates how this works for a specific product:

<figure><img src="/files/bfa9135e540206d47d394b7882c7f0cc200d20ea" alt=""><figcaption></figcaption></figure>

In the screenshot below, you can see how this rule would work for a specific product:

<figure><img src="/files/b6be9292344d1511c25c31780da46841a3f1d491" alt=""><figcaption></figcaption></figure>

### Calculate List Length (Unique Elements)

This is an extension of the “calculate list length” rule. It allows the user to count only unique elements in a list. This can be useful for ensuring that duplicate sizes are not counted multiple times.

For instance, if you have a list of sizes for a product, you can use this extension of the rule to determine how many unique sizes are available. In the screenshot below, you can see how this rule would work for a specific product:

<figure><img src="/files/0a4cd6a599f8b058410bdec9a4b61df2e95125ce" alt=""><figcaption></figcaption></figure>

In the screenshot below, you can see how counting only unique values in a rule works for a specific product:

<figure><img src="/files/e0833868705c4ef89569cfca6963346c32875879" alt=""><figcaption></figcaption></figure>


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