Is my brooder large enough?

We are getting chickens soon, and have set up a brooder for them. The question is... is it big enough? It is a dog crate approximately 2'x1.5'. The brooder will hold 3 chicks. There is room for them to move in and out of the heat lamp and room for their feeder and waterer. The chicks will have some time out of the coop to stretch their legs and run around. But is that size big enough?