# How to use math functions in price formulas

The price formula field type in WooCommerce Product Options allows store owners to create custom calculations for product prices based on information that the customer provides. Price formulas can be very simple or very complex!

This article provides details of how to use advanced mathematical formulas in your price formulas. The following information is just a starting point and you can use any of the mathematical operators documented in this JavaScript formula parser, which WooCommerce Product Options uses under the covers.

## Available variables

You can use price formulas to calculate the final price of a product based on variables such as:

- Numbers entered by the customer. These must come from number fields which are in the same product options group as the price formula field.
- The base price of the current product
`[product_price]`

.

## Mathematical operators

The price formula field type supports common mathematical operators, such as `+`

, `-`

, `*`

and `/`

. In addition, it can parse all the mathematical functions included in the Javascript `Math`

object.

A complete list of those functions can be found on the Javascript Math page of the MDN Web Docs.Â Those functions can be used by entering their name (without the `Math.`

prefix itself) in the formula. Below, we will explore some practical examples to help you to apply this to different use cases.

### How to limit prices

The functions `min`

and `max`

allow you to set a minimum or maximum price that can be charged. For example, you might be selling made-to-measure curtainsÂ (like in this demo product) and want to charge a minimum of $50 and a maximum of $500, regardless of the measurements entered.

You should use the `max`

function to set a * minimum price* and the

`min`

function to set a *. (We realise this is the opposite of what you might expect linguistically - this is how these mathematical functions work and is not specific to the WooCommerce Product Options plugin ðŸ™ƒ)*

**maximum price**#### Example: max

*Use this to set a minimum price for the price formula.*

A store sells made-to-measure curtains. The product costs **$50 per square meter**. Customers are asked to enter the **width** and **height** they need â€“ in cm â€“ but they will incur a minimum charge of **$50** regardless of the total size being ordered.

You can achieve this with the following formula:

`max( 50, ( [width] / 100 ) * ( [height] / 100 ) * [product_price] )`

In the formula above, the function will return `[width] * [height] * [product_price]`

if it is more than `50`

. Otherwise, it will always return `50`

, no matter how small the values for `[width]`

and `[height]`

are.

For example, when **width** is **100** and **height** is **50**, the formula is calculated as follows:

`max( 50, ( 100 / 100 ) * ( 50 / 100 ) * 50 ) = max( 50, 1 * 0.5 * 50 ) = max( 50, 25 ) = 50`

#### Example: min

*Use this to set a maximum price for the price formula.*

A store sells guided tours of archeological sites. Tourists pay a fee of **$10 per ticket** but larger groups can get a deal because the tour is capped at a maximum charge of **$400** (corresponding to **40 people**) but can accommodate up to **50 people** (so every person in that group exceeding 40 people gets to participate for free).

You can achieve this with the following formula:

`min( 400, [tickets] * [product_price] )`

In the formula above, the function will return `[tickets] * [product_price]`

if it is less than `400`

. Otherwise, it will always return `400`

, no matter how large the value for `[tickets]`

is.

For example, when the number of** tickets** is **48**, the formula is calculated as follows:

`min( 400, 48 * 10 ) = min( 400, 480 ) = 400`

### How to round prices

You can round the value of a calculated price by using function among `round`

, `trunc`

, `floor`

and `ceil`

, with the following specifications:

`round`

approximates the value to the closest integer (e.g`round( 3.37 )`

returns`3`

;`round( 5.98 )`

returns 6).`floor`

returns the closest integer smaller than the input value (e.g`floor( 3.37 )`

returns`3`

;`floor( 5.98 )`

returns`5`

).`trunc`

truncates the decimal portion of a number (e.g.`trunc( 3.37 )`

returns 3;Â`floor( 5.98 )`

returns`5`

). With positive numbers,`trunc`

and`floor`

both return the same value.`ceil`

Â returns the closest integer greater than the input value (e.g`floor( 3.37 )`

returns`4`

;`floor( 5.98 )`

returns`6`

).

#### Example: ceil

A store sells pet food. Dog food is **$28.15 per kg**. Customers can enter the required **weight** with **0.1 kg precision**. The shop owner wants prices to be calculated to the whole dollar, approximating by excess. The appropriate formula is:

`ceil( [weight] * [product_price] )`

For example, if **2.5** is entered as **weight**, the formula is calculated as follows:

`ceil( 2.5 * 28.15 ) = ceil( 70.375 ) = 71`

#### Example: round

A website provides housekeeping services and allows customers to book cleaners in **1-hour slots**. The cost for **1 hour** is **$19.85** and the site owner wants to round the price calculation in **$5 increments** so that **$19.85** returns **$20** and **$357.30** returns **$355**. The appropriate formula is:

`5 * round( [hours] * [product_price] / 5 )`

For example, if a customer requests **18** hours, the formula is calculated as follows:

`5 * round( 18 * 19.85 / 5 ) = 5 * round( 71.46 ) = 5 * 71 = 355`

### Logical or conditional clauses

Price formulas are limited to mathematical operations and do not understand logical structures. Therefore, expressions like `if ( [width] < 200 ) then [product_price] else 1.25 * [product_price]`

**cannot be used** in a price formula. Instead, you can use mathematical functions and operators to transform logical clauses into numbers.

#### Equivalence between logical and mathematical constants and operators

The basic equivalencies between logic and maths are:

`true`

and`false`

are equivalent to`1`

and`0`

, respectively`a AND b`

is equivalent to a multiplication`a * b`

`a OR b`

is equivalent to an addition`a + b`

`a > b`

can be written as`max( 0, sign( a - b ) )`

`a < b`

can be written as`max( 0, sign( b - a ) )`

Let's see how this can help us write conditional structures in the context of price formulas. Please consider the following example. A store sells shipping services and doubles its rates for oversized items. Users are invited to enter the **Width**, **Height** and **Depth** of the package they need to ship. The store considers a package oversized **if the sum of the three lengths is more than 100 centimeters**. In a regular coding language, one would write:

**if** [Width] + [Height] + [Depth] > 100 **then** 2 * [product_price] **else** [product_price]

but we cannot write this in a price formula. What we would write is:

`[product_price] * (1 + max( 0, sign( [Width] + [Height] + [Depth] - 100 ) ) )`

The function `sign`

returns **1**, **-1** or **0** depending on the passed parameter being positive, negative or zero. Since `max`

forces the result to be greater than 0, what the function does is return **1** if **[Width] + [Height] + [Depth]** is greater than 100 and 0 otherwise.

For example, if a customer wants to ship a package that is **45 cm** wide, **40 cm** high and **20 cm** deep, the formula is calculated as follows:

`[product_price] * ( 1 + max( 0, sign( 45 + 40 + 20 - 100 ) ) ) =`

[product_price] * ( 1 + max( 0, sign( 5 ) ) ) =

[product_price] * ( 1 + max( 0, 1 ) ) =

[product_price] * ( 1 + 1 ) =

[product_price] * 2

#### How to use AND/OR logic in a price formula

As described above, you must use mathematical operators in order to add AND/OR logic. Specifically:

- Use addition (the
`+`

sign) for OR logic. - Use multiplication (the
`*`

sign) for AND logic.

For example: `[Sides.Front.checked] * [Sides.Back.checked] * 10`

translates into *"If BOTH front AND back sides are checked then add 10 to the formula"*, whereas `( [Sides.Front.checked] + [Sides.Front.checked] ) * 10 / [Sides.count]`

translates into *"If EITHER the front OR the back side are checked add 10 to the formula"*.

### Related Articles

- How to add custom code snippets to your website
- How to only display variation names in the 'Products' option type
- How to import and export product options
- How does the plugin work with the REST API?
- Can I export product add-ons to my CRM or mailing list?
- How can I change or translate the error messages in WooCommerce Product Options?