# sizeBySpeed

> Script interface for the SizeBySpeedModule of a Particle System.

## Definition

* **Type:** Property
* **Namespace:** [UnityEngine](/engine/6000.5/script-reference/unityengine.md)
* **Assembly:** UnityEngine.ParticleSystemModule

```csharp
public ParticleSystem.SizeBySpeedModule sizeBySpeed { get; }
```

### Remarks

This module controls the size of particles based on their speeds.

Particle System modules do not need to be reassigned back to the system; they are interfaces and not independent objects.

### Examples

```csharp
using UnityEngine;
using System.Collections;

[RequireComponent(typeof(ParticleSystem))]
public class ExampleClass : MonoBehaviour {
    void Start() {
        ParticleSystem ps = GetComponent<ParticleSystem>();
        var ss = ps.sizeBySpeed;
        ss.enabled = true;
        ss.range = new Vector2(0.0f, 2.0f);

        AnimationCurve curve = new AnimationCurve();
        curve.AddKey(0.0f, 0.1f);
        curve.AddKey(0.75f, 1.0f);
        ss.size = new ParticleSystem.MinMaxCurve(10.0f, curve);
    }
}
```