---
title: relativeStrengthIndex() function
description: relativeStrengthIndex() measures the relative speed and change of values in input tables.
url: https://docs.influxdata.com/flux/v0/stdlib/universe/relativestrengthindex/
estimated_tokens: 1518
product: Flux
version: v0
---

# relativeStrengthIndex() function

-   Flux 0.38.0+
-   View InfluxDB support

`relativeStrengthIndex()` measures the relative speed and change of values in input tables.

### Relative strength index (RSI) rules

-   The general equation for calculating a relative strength index (RSI) is `RSI = 100 - (100 / (1 + (AVG GAIN / AVG LOSS)))`.
-   For the first value of the RSI, `AVG GAIN` and `AVG LOSS` are averages of the `n` period.
-   For subsequent calculations:
    -   `AVG GAIN` = `((PREVIOUS AVG GAIN) * (n - 1)) / n`
    -   `AVG LOSS` = `((PREVIOUS AVG LOSS) * (n - 1)) / n`
-   `relativeStrengthIndex()` ignores `null` values.

### Output tables

For each input table with `x` rows, `relativeStrengthIndex()` outputs a table with `x - n` rows.

##### Function type signature

```js
(<-tables: stream[A], n: int, ?columns: [string]) => stream[B] where A: Record, B: Record
```

For more information, see [Function type signatures](/flux/v0/function-type-signatures/).

## Parameters

### n

(Required) Number of values to use to calculate the RSI.

### columns

Columns to operate on. Default is `["_value"]`.

### tables

Input data. Default is piped-forward data (`<-`).

## Examples

### Calculate a three point relative strength index

```js
import "sampledata"

sampledata.int()
    |> relativeStrengthIndex(n: 3)
```

[](#view-example-input-and-output)

View example input and output

#### Input data

| _time | _value | *tag |
| --- | --- | --- |
| 2021-01-01T00:00:00Z | -2 | t1 |
| 2021-01-01T00:00:10Z | 10 | t1 |
| 2021-01-01T00:00:20Z | 7 | t1 |
| 2021-01-01T00:00:30Z | 17 | t1 |
| 2021-01-01T00:00:40Z | 15 | t1 |
| 2021-01-01T00:00:50Z | 4 | t1 |

| _time | _value | *tag |
| --- | --- | --- |
| 2021-01-01T00:00:00Z | 19 | t2 |
| 2021-01-01T00:00:10Z | 4 | t2 |
| 2021-01-01T00:00:20Z | -3 | t2 |
| 2021-01-01T00:00:30Z | 19 | t2 |
| 2021-01-01T00:00:40Z | 13 | t2 |
| 2021-01-01T00:00:50Z | 1 | t2 |

#### Output data

| _time | _value | *tag |
| --- | --- | --- |
| 2021-01-01T00:00:30Z | 84.375 | t1 |
| 2021-01-01T00:00:40Z | 73.97260273972603 | t1 |
| 2021-01-01T00:00:50Z | 36.672325976230894 | t1 |

| _time | _value | *tag |
| --- | --- | --- |
| 2021-01-01T00:00:30Z | 70.27027027027026 | t2 |
| 2021-01-01T00:00:40Z | 59.42857142857142 | t2 |
| 2021-01-01T00:00:50Z | 40.625 | t2 |

#### Related

-   [movingAverage() function](/flux/v0/stdlib/universe/movingaverage/)
-   [timedMovingAverage() function](/flux/v0/stdlib/universe/timedmovingaverage/)
-   [exponentialMovingAverage() function](/flux/v0/stdlib/universe/exponentialmovingaverage/)
-   [InfluxQL RELATIVE\_STRENGTH\_INDEX()](/influxdb/v1/query_language/functions/#relative-strength-index)

[transformations](/flux/v0/tags/transformations/)