---
title: "Performance Metrics"
description: "Learn how to attach performance metrics to your transactions or spans."
url: https://docs.sentry.io/platforms/dart/guides/flutter/tracing/instrumentation/performance-metrics/
---

# Performance Metrics | Sentry for Flutter

Sentry's SDKs support sending performance metrics data to Sentry. These are numeric values attached to transactions or spans that are aggregated and displayed in Sentry.

If configured, the Flutter SDK automatically collects the following performance metrics:

* [Cold and warm app start time](https://docs.sentry.io/platforms/dart/guides/flutter/tracing/instrumentation/automatic-instrumentation.md#app-start-instrumentation).
* [Slow and frozen frame rendering](https://docs.sentry.io/platforms/dart/guides/flutter/tracing/instrumentation/automatic-instrumentation.md#slow-and-frozen-frames).

## [Custom Measurements](https://docs.sentry.io/platforms/dart/guides/flutter/tracing/instrumentation/performance-metrics.md#custom-measurements)

Sentry supports **custom performance measurements** on transactions: you define measurements that matter to your application (for example, memory usage, query time, or user action counts) and send them with the transaction from your SDK. They appear in **Dashboards**, **Discover**, and transaction trace detail. You can define up to 10 custom measurements per transaction; any additional ones are truncated. Configure and send them in your SDK; supported platforms:

* [Android (version `6.5.0` or later)](https://docs.sentry.io/platforms/android/performance/instrumentation/performance-metrics.md)
* [Apple (version `7.28.0` or later)](https://docs.sentry.io/platforms/apple/performance/instrumentation/performance-metrics.md)
* [Dart (version `6.11.0` or later)](https://docs.sentry.io/platforms/dart/performance/instrumentation/performance-metrics.md)
* [Flutter (version `6.11.0` or later)](https://docs.sentry.io/platforms/dart/guides/flutter/performance/instrumentation/performance-metrics.md)
* [Java (version `6.5.0` or later)](https://docs.sentry.io/platforms/java/performance/instrumentation/performance-metrics.md)
* [JavaScript (version `7.0.0` or later)](https://docs.sentry.io/platforms/javascript/performance/instrumentation/performance-metrics.md)
* [.NET (version `3.23.0` or later)](https://docs.sentry.io/platforms/dotnet/performance/instrumentation/performance-metrics.md)
* [Python (version `1.5.12` or later)](https://docs.sentry.io/platforms/python/tracing/instrumentation/custom-instrumentation.md)
* [React Native (version `4.0.0` or later)](https://docs.sentry.io/platforms/react-native/performance/instrumentation/performance-metrics.md)
* [Ruby (version `5.8.0` or later)](https://docs.sentry.io/platforms/ruby/performance/instrumentation/performance-metrics.md)
* [Rails (version `5.8.0` or later)](https://docs.sentry.io/platforms/ruby/guides/rails/performance/instrumentation/performance-metrics.md)

To set a performance measurement, you need to supply the following:

* name (`string`)
* value (any numeric type - `float`, `integer`, etc.)
* unit (`string`, defaults to the string `none` if omitted)

Sentry supports adding arbitrary custom units, but we recommend using one of the [supported units listed below](https://docs.sentry.io/platforms/dart/guides/flutter/tracing/instrumentation/performance-metrics.md#supported-measurement-units).

Adding custom measurements is supported in Sentry's Dart/Flutter SDK version `6.11.0` and above.

* Transaction mode (default): Use `setMeasurement` on the active span.
* [Stream mode](https://docs.sentry.io/platforms/dart/guides/flutter/tracing/streamed-spans.md): There's no dedicated measurement API (and no public way to fetch the active span), so record the values as attributes on a span you create.

**Transaction Mode (Default)**

```dart
import 'package:sentry/sentry.dart';

final transaction = Sentry.getSpan();

// Record amount of memory used
transaction?.setMeasurement('memoryUsed', 123,
    unit: SentryMeasurementUnit.byte);

// Record time when Footer component renders on page
transaction?.setMeasurement('ui.footerComponent.render', 1.3,
    unit: SentryMeasurementUnit.second);

// Record amount of times localStorage was read
transaction?.setMeasurement('localStorageRead', 4);
```

**Stream Mode**

```dart
import 'package:sentry/sentry.dart';

await Sentry.startSpan('my-operation', (span) async {
  // Record custom measurements as span attributes.
  span.setAttribute('memoryUsed', SentryAttribute.int(123));
  span.setAttribute('ui.footerComponent.render', SentryAttribute.double(1.3));
  span.setAttribute('localStorageRead', SentryAttribute.int(4));
});
```

Currently, unit conversion is only supported once the data has already been stored. This means that, for example, `('myMeasurement', 60, 'second')` and `('myMeasurement', 3, 'minute')` would not be aggregated, but rather stored as two separate measurements. To avoid this, make sure to use a consistent unit when recording a custom measurement.

## [Supported Measurement Units](https://docs.sentry.io/platforms/dart/guides/flutter/tracing/instrumentation/performance-metrics.md#supported-measurement-units)

Units augment measurement values by giving meaning to what otherwise might be abstract numbers. Adding units also allows Sentry to offer controls - unit conversions, filters, and so on - based on those units. For values that are unitless, you can supply an empty string or `none`.

### [Duration Units](https://docs.sentry.io/platforms/dart/guides/flutter/tracing/instrumentation/performance-metrics.md#duration-units)

* `nanosecond`
* `microsecond`
* `millisecond`
* `second`
* `minute`
* `hour`
* `day`
* `week`

### [Information Units](https://docs.sentry.io/platforms/dart/guides/flutter/tracing/instrumentation/performance-metrics.md#information-units)

* `bit`
* `byte`
* `kilobyte`
* `kibibyte`
* `megabyte`
* `mebibyte`
* `gigabyte`
* `gibibyte`
* `terabyte`
* `tebibyte`
* `petabyte`
* `pebibyte`
* `exabyte`
* `exbibyte`

### [Fraction Units](https://docs.sentry.io/platforms/dart/guides/flutter/tracing/instrumentation/performance-metrics.md#fraction-units)

* `ratio`
* `percent`

If you want to explore further, you can find details about supported units in our [event ingestion documentation](https://getsentry.github.io/relay/relay_metrics/enum.MetricUnit.html).