AWS instance type for service dialog

I am creating a service catalog for AWS provisioning. I want the end user to be able to select the vm_name and instance_type. vm_name works well but when I pass instance_type as t2.nano I get [NoMethodError]: undefined method 'name' for nil:NilClass]

Googling around I see that the instance_name parameter uses the ID rather than the name. How do I find out what the ID for different instance types is?

Any help is greatly appreciated