---
title: birthRateVariation
framework: scenekit
role: symbol
role_heading: Instance Property
path: scenekit/scnparticlesystem/birthratevariation
---

# birthRateVariation

The range of randomized particle birth rate values. Animatable.

## Declaration

```swift
var birthRateVariation: CGFloat { get set }
```

## Discussion

Discussion Setting a nonzero value for this property randomizes the effect of the birthRate property. For each emission period, SceneKit randomly adjusts the birth rate by up to half the birthRateVariation value. For example, if the birthRate value is 100 particles and the birthRateVariation value is 50 particles, the system randomly emits between 75 and 125 particles during its emissionDuration period. The default value is 0.0 seconds, specifying no randomization. You can animate changes to this property’s value. See Animating SceneKit Content.

## See Also

### Managing Particle Emission Timing

- [emissionDuration](scenekit/scnparticlesystem/emissionduration.md)
- [emissionDurationVariation](scenekit/scnparticlesystem/emissiondurationvariation.md)
- [idleDuration](scenekit/scnparticlesystem/idleduration.md)
- [idleDurationVariation](scenekit/scnparticlesystem/idledurationvariation.md)
- [loops](scenekit/scnparticlesystem/loops.md)
- [warmupDuration](scenekit/scnparticlesystem/warmupduration.md)
- [birthRate](scenekit/scnparticlesystem/birthrate.md)