How do I calculate the broadcast address?

The broadcast address is based on your IP address and subnet mask. For example, if your IP address is 10.11.12.100, and your mask is 255.255.255.0, then your broadcast will be 10.11.12.255.

If you have a more exotic subnet mask, there are actually many websites that will calculate the broadcast address for you.

You can use sites like this to calculate your broadcast address:
http://www.tech-faq.com/calculate-broadcast-address