# Rate Configuration

* Does your crowdsale sell tokens at a fixed price?
* Does the price change over time or as a function of demand?

Understanding the rate of a crowdsale is super important, and mistakes here are a common source of bugs.

In Ether, the smallest unit of the currency is wei, and `1 ETH === 10^18 wei` . You will have to set the number of tokens per wei payed.