Even if you're pretty good at doing math in your head, there are so many different measures that you may often find yourself needing to do conversions. For example, when I'm watching tennis on TV and the announcer says the serve was 220 kilometers per hour, I'm fairly clueless. So I just ask Siri to convert to the more familiar mph. (And that would be 137 mph—definitely a fast serve.) Siri can convert currencies and also measures such as distance, weight, volume, cooking measures, temperature, and speed. Plus, since the introduction of iOS 9, there are two ways to get Siri to do conversions: ask Siri or use Spotlight Search—which is basically sending Siri a text message.