usedSpace("/")
–>　　8.4346003456E+10

usedSpace2("/")
–>　　8.4345450496E+10

usedSpaceString("/")
–>　　"84.35 GB"

usedSpaceLongString("/")
–>　　"45.77 GB (45,772,857,344 bytes)"–English user environment
–>　　"45.77 GB (45,772,857,344 バイト)"–Japanese user environment

tell application "Finder"
　　free space of startup disk
end tell
–>　　4.5784592712E+10

on usedSpace(volumePath)
　　set theNSURL to current application’s class "NSURL"’s fileURLWithPath:volumePath –considering "ASOC in Xcode"
　　set {theResult, theSize} to theNSURL’s getResourceValue:(reference) forKey:(current application’s NSURLVolumeAvailableCapacityKey) |error|:(missing value)
　　
　　return theSize as real — integer may be too big for AS
end usedSpace

on usedSpace2(volumePath)
　　set fileAttr to current application’s NSFileManager’s defaultManager()’s attributesOfFileSystemForPath:volumePath |error|:(missing value)
　　
　　return (fileAttr’s objectForKey:(current application’s NSFileSystemFreeSize)) as real — integer may be too big for AS
end usedSpace2

on usedSpaceString(volumePath)
　　set fileAttr to current application’s NSFileManager’s defaultManager()’s attributesOfFileSystemForPath:volumePath |error|:(missing value)
　　set fRes to fileAttr’s objectForKey:(current application’s NSFileSystemFreeSize)
　　
　　–Formatting
　　set sizeString to current application’s NSByteCountFormatter’s stringFromByteCount:fRes countStyle:(current application’s NSByteCountFormatterCountStyleDecimal)
　　
　　return sizeString as text
end usedSpaceString

on usedSpaceLongString(volumePath)
　　set fileAttr to current application’s NSFileManager’s defaultManager()’s attributesOfFileSystemForPath:volumePath |error|:(missing value)
　　set fRes to fileAttr’s objectForKey:(current application’s NSFileSystemFreeSize)
　　
　　–Formatting
　　set theFormatter to current application’s NSByteCountFormatter’s alloc()’s init()
　　theFormatter’s setCountStyle:(current application’s NSByteCountFormatterCountStyleDecimal)
　　theFormatter’s setIncludesActualByteCount:true
　　set sizeString to theFormatter’s stringFromByteCount:fRes
　　
　　return sizeString as text
end usedSpaceLongString