How do I determine which iOS SDK I have?

If you type this:

$> xcodebuild -showsdks

it gives something like this:

$> OS X SDKs:
    OS X 10.8                       -sdk macosx10.8
    OS X 10.9                       -sdk macosx10.9

iOS SDKs:
    iOS 6.1                         -sdk iphoneos6.1
    iOS 7.0                         -sdk iphoneos7.0

iOS Simulator SDKs:
    Simulator - iOS 6.0             -sdk iphonesimulator6.0
    Simulator - iOS 6.1             -sdk iphonesimulator6.1
    Simulator - iOS 7.0             -sdk iphonesimulator7.0