---
title: Ranking functions
slug: '1448'
canonical_url: https://docs.coveo.com/en/1448/
collection: build-a-search-ui
source_format: adoc
---
# Ranking functions
A [ranking function](https://docs.coveo.com/en/237/) is a mathematical expression evaluated against each [item](https://docs.coveo.com/en/210/) returned by a [query](https://docs.coveo.com/en/231/).
The [ranking function](https://docs.coveo.com/en/237/) output for a given [item](https://docs.coveo.com/en/210/) generates a boost which is then added to the ranking score of that [item](https://docs.coveo.com/en/210/).

This article describes the members of the structure that defines a single [ranking function](https://docs.coveo.com/en/237/).
You can specify an array of [ranking functions](https://docs.coveo.com/en/237/) in a query using the [`rankingFunctions`](https://docs.coveo.com/en/13#operation/searchUsingPost-rankingFunctions) top-level query parameter.

> **Important**
>
> Ranking functions operate with floating-point precision rather than integers.
> As a result, calculations may introduce minor inaccuracies due to the inherent limitations of floating-point arithmetic.
> 
> Using ranking functions with dates or other data requiring high precision isn't recommended, unless some imprecision is acceptable for your use case.
> For scenarios in which precision is critical, use [query ranking expressions (QREs)](https://docs.coveo.com/en/1472/) instead.

## Example

You want to increase the ranking score of restaurant [items](https://docs.coveo.com/en/210/) by an amount varying from `0` to `500`, depending on their proximity to the user's location.

```http
POST https://platform.cloud.coveo.com/rest/search/v2 HTTP/1.1
​
Content-Type: application/json
Accept: application/json
Authorization: Bearer **********-****-****-****-************
```

**Payload:**

```json
{
  "aq": "documenttype==Restaurant",
  "rankingFunctions": [
    {
      "expression": "-sqrt(dist(@longitude, @latitude, 47.4953481, -121.7885868))",
      "normalizeWeight": true,
      "modifier": 500
    }
  ]
}
```

**200 OK response body (excerpt):**

```json
{
  ...
  "results": [
    {
      ...
      "score": 1642,
      "raw": {
        ...
        "latitude": -121.7890394,
        "longitude": 47.4951689
        ...
      },
      ...
      "title": "Double R Diner",
      ...
    },
    ...
  ],
  ...
}
```

> **Note**
>
> Suppose that the values returned by the `+-sqrt(dist(...))+` function for a [query](https://docs.coveo.com/en/231/) are in the range `[-1000, 0]`.
> 
> The result for a restaurant [item](https://docs.coveo.com/en/210/) that has a `+-sqrt(dist(...))+` value of:
> 
> * `-1000` has a ranking score boost of `0` (0% of 500).
> 
> * `-750` has ranking score boost of `125` (25% of 500).
> 
> * `-500` has ranking score boost of `250` (50% of 500).
> 
> * `-250` has a ranking score boost of `375` (75% of 500).
> 
> * `0` has a ranking score boost of `500` (100% of 500).

## Reference

See the [`rankingFunctions` reference documentation](https://docs.coveo.com/en/13#operation/searchUsingGet-rankingFunctions).