---
title: Find percentile and quantile values
description: Use the quantile() function to return all values within the q quantile or percentile of input data.
url: https://docs.influxdata.com/influxdb/v2/query-data/flux/percentile-quantile/
estimated_tokens: 2634
product: InfluxDB OSS v2
version: v2
---

# Find percentile and quantile values

This page documents an earlier version of InfluxDB OSS. [InfluxDB 3 Core](/influxdb3/core/) is the latest stable version.

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Use the [`quantile()` function](/flux/v0/stdlib/universe/quantile/) to return a value representing the `q` quantile or percentile of input data.

## Percentile versus quantile

Percentiles and quantiles are very similar, differing only in the number used to calculate return values. A percentile is calculated using numbers between `0` and `100`. A quantile is calculated using numbers between `0.0` and `1.0`. For example, the **`0.5` quantile** is the same as the **50th percentile**.

## Select a method for calculating the quantile

Select one of the following methods to calculate the quantile:

-   [estimate\_tdigest](#estimate_tdigest)
-   [exact\_mean](#exact_mean)
-   [exact\_selector](#exact_selector)

### estimate\_tdigest

**(Default)** An aggregate method that uses a [t-digest data structure](https://github.com/tdunning/t-digest) to compute a quantile estimate on large data sources. Output tables consist of a single row containing the calculated quantile.

If calculating the `0.5` quantile or 50th percentile:

**Given the following input table:**

| _time | _value |
| --- | --- |
| 2020-01-01T00:01:00Z | 1.0 |
| 2020-01-01T00:02:00Z | 1.0 |
| 2020-01-01T00:03:00Z | 2.0 |
| 2020-01-01T00:04:00Z | 3.0 |

**`estimate_tdigest` returns:**

| _value |
| --- |
| 1.5 |

### exact\_mean

An aggregate method that takes the average of the two points closest to the quantile value. Output tables consist of a single row containing the calculated quantile.

If calculating the `0.5` quantile or 50th percentile:

**Given the following input table:**

| _time | _value |
| --- | --- |
| 2020-01-01T00:01:00Z | 1.0 |
| 2020-01-01T00:02:00Z | 1.0 |
| 2020-01-01T00:03:00Z | 2.0 |
| 2020-01-01T00:04:00Z | 3.0 |

**`exact_mean` returns:**

| _value |
| --- |
| 1.5 |

### exact\_selector

A selector method that returns the data point for which at least `q` points are less than. Output tables consist of a single row containing the calculated quantile.

If calculating the `0.5` quantile or 50th percentile:

**Given the following input table:**

| _time | _value |
| --- | --- |
| 2020-01-01T00:01:00Z | 1.0 |
| 2020-01-01T00:02:00Z | 1.0 |
| 2020-01-01T00:03:00Z | 2.0 |
| 2020-01-01T00:04:00Z | 3.0 |

**`exact_selector` returns:**

| _time | _value |
| --- | --- |
| 2020-01-01T00:02:00Z | 1.0 |

The examples below use the [example data variable](/influxdb/v2/query-data/flux/#example-data-variable).

## Find the value representing the 99th percentile

Use the default method, `"estimate_tdigest"`, to return all rows in a table that contain values in the 99th percentile of data in the table.

```js
data
    |> quantile(q: 0.99)
```

## Find the average of values closest to the quantile

Use the `exact_mean` method to return a single row per input table containing the average of the two values closest to the mathematical quantile of data in the table. For example, to calculate the `0.99` quantile:

```js
data
    |> quantile(q: 0.99, method: "exact_mean")
```

## Find the point with the quantile value

Use the `exact_selector` method to return a single row per input table containing the value that `q * 100`% of values in the table are less than. For example, to calculate the `0.99` quantile:

```js
data
    |> quantile(q: 0.99, method: "exact_selector")
```

## Use quantile() with aggregateWindow()

[`aggregateWindow()`](/flux/v0/stdlib/universe/aggregatewindow/) segments data into windows of time, aggregates data in each window into a single point, and then removes the time-based segmentation. It is primarily used to [downsample data](/influxdb/v2/process-data/common-tasks/downsample-data/).

To specify the [quantile calculation method](#select-a-method-for-calculating-the-quantile) in `aggregateWindow()`, use the [full function syntax](/flux/v0/stdlib/universe/aggregatewindow/#specify-parameters-of-the-aggregate-function):

```js
data
    |> aggregateWindow(
        every: 5m,
        fn: (tables=<-, column) => tables
            |> quantile(q: 0.99, method: "exact_selector"),
    )
```

#### Related

-   [quantile() function](/flux/v0/stdlib/universe/quantile/)

[query](/influxdb/v2/tags/query/) [percentile](/influxdb/v2/tags/percentile/) [quantile](/influxdb/v2/tags/quantile/)