# Function: clutchSize()

[**lifecycle-kit**](https://jonbogaty.com/lifecycle-kit/api/readme/index.md)

***

[lifecycle-kit](https://jonbogaty.com/lifecycle-kit/api/readme/index.md) / [bio-laws](https://jonbogaty.com/lifecycle-kit/api/bio-laws/readme/index.md) / clutchSize


# Function: clutchSize() {#function-clutchsize}


> **clutchSize**(`parentMass`, `offspringMass`, `rSelected?`): `number`

Defined in: [bio-laws/lifeHistory.ts:69](https://github.com/jbcom/lifecycle-kit/blob/074e4e7b8038d3e2de9eb44c4b5b5aee0ef02b48/src/bio-laws/lifeHistory.ts#L69)

Offspring count from the size/number trade-off.

Source: Charnov, E.L. & Ernest, S.K.M. (2006). "The offspring-size/
clutch-size trade-off in mammals." The American Naturalist, 167(4), 578-582.

Total reproductive output is roughly constant for a given parent mass, so a
lineage chooses between many small offspring and few large ones — it cannot
have both. r-selected strategies allocate ~25% of body mass to reproduction;
K-selected ~10%.

This is the real content of "reproductive strategy": not which container the
offspring arrives in, but how the parent divides a fixed budget.


## Parameters {#parameters}



### parentMass {#parentmass}


`number`


### offspringMass {#offspringmass}


`number`


### rSelected? {#rselected}


`boolean` = `false`


## Returns {#returns}


`number`