> For the complete documentation index, see [llms.txt](https://docs.roboflow.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.roboflow.com/workflows/blocks/blocks/classical-computer-vision/size-measurement.md).

# Size Measurement

The **Size Measurement Block**

## How This Block Works

youtube.com/watch?v=FQY7TSHfZeI) calculates the dimensions of objects relative to a reference object. It uses one model to detect the reference object and another to detect the objects to measure. The block outputs the dimensions of the objects in terms of the reference object.

* **Reference Object**: This is the known object used as a baseline for measurements. Its dimensions are known and used to scale the measurements of other objects.
* **Object to Measure**: This is the object whose dimensions are being calculated. The block measures these dimensions relative to the reference object.

### Block Usage

To use the Size Measurement Block, follow these steps:

1. **Select Models**: Choose a model to detect the reference object and another model to detect the objects you want to measure.
2. **Configure Inputs**: Provide the predictions from both models as inputs to the block.
3. **Set Reference Dimensions**: Specify the known dimensions of the reference object in the format 'width,height' or as a tuple (width, height).
4. **Run the Block**: Execute the block to calculate the dimensions of the detected objects relative to the reference object.

### Example

Imagine you have a scene with a calibration card and several packages. The calibration card has known dimensions of 5.0 inches by 3.0 inches. You want to measure the dimensions of packages in the scene.

* **Reference Object**: Calibration card with dimensions 5.0 inches (width) by 3.0 inches (height).
* **Objects to Measure**: Packages detected in the scene.

The block will use the known dimensions of the calibration card to calculate the dimensions of each package. For example, if a package is detected with a width of 100 pixels and a height of 60 pixels, and the calibration card is detected with a width of 50 pixels and a height of 30 pixels, the block will calculate the package's dimensions as:

* **Width**: (100 pixels / 50 pixels) \* 5.0 inches = 10.0 inches
* **Height**: (60 pixels / 30 pixels) \* 3.0 inches = 6.0 inches

This allows you to obtain the real-world dimensions of the packages based on the reference object's known size.

[Watch the video tutorial](https://www.youtube.com/watch?v=FQY7TSHfZeI)

### Type identifier

Use the following identifier in step `"type"` field: `roboflow_core/size_measurement@v1` to add the block as a step in your workflow.

### Properties

| **Name**                | **Type**                                       | **Description**                                                                                                                                                | Refs |
| ----------------------- | ---------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---- |
| `name`                  | `str`                                          | Enter a unique identifier for this step..                                                                                                                      | ❌    |
| `reference_predictions` | `List[Any]`                                    | Reference object used to calculate the dimensions of the specified objects. If multiple objects are provided, the highest confidence prediction will be used.. | ✅    |
| `reference_dimensions`  | `Union[List[float], Tuple[float, float], str]` | Dimensions of the reference object in desired units, (e.g. inches). Will be used to convert the pixel dimensions of the other objects to real-world units..    | ✅    |

The **Refs** column marks possibility to parametrise the property with dynamic values available in `workflow` runtime. See *Bindings* for more info.

### Input and Output Bindings

The available connections depend on its binding kinds. Check what binding kinds `Size Measurement` in version `v1` has.

<details>

<summary>Input and output bindings</summary>

* input
  * `object_predictions` (*Union\[*[*`instance_segmentation_prediction`*](/workflows/developer-guide/developer-guide/kinds/instance-segmentation-prediction.md)*,* [*`object_detection_prediction`*](/workflows/developer-guide/developer-guide/kinds/object-detection-prediction.md)*]*): Model predictions to measure the dimensions of..
  * `reference_predictions` (*Union\[*[*`instance_segmentation_prediction`*](/workflows/developer-guide/developer-guide/kinds/instance-segmentation-prediction.md)*,* [*`list_of_values`*](/workflows/developer-guide/developer-guide/kinds/list-of-values.md)*,* [*`object_detection_prediction`*](/workflows/developer-guide/developer-guide/kinds/object-detection-prediction.md)*]*): Reference object used to calculate the dimensions of the specified objects. If multiple objects are provided, the highest confidence prediction will be used..
  * `reference_dimensions` (*Union\[*[*`list_of_values`*](/workflows/developer-guide/developer-guide/kinds/list-of-values.md)*,* [*`string`*](/workflows/developer-guide/developer-guide/kinds/string.md)*]*): Dimensions of the reference object in desired units, (e.g. inches). Will be used to convert the pixel dimensions of the other objects to real-world units..
* output
  * `dimensions` ([`list_of_values`](/workflows/developer-guide/developer-guide/kinds/list-of-values.md)): List of values of any type.

</details>

<details>

<summary>Example JSON definition</summary>

```json
{
	    "name": "<your_step_name_here>",
	    "type": "roboflow_core/size_measurement@v1",
	    "object_predictions": "$segmentation.object_predictions",
	    "reference_predictions": "$segmentation.reference_predictions",
	    "reference_dimensions": [
	        4.5,
	        3.0
	    ]
	}
```

</details>