From Xojo Documentation

Read-Only Property (As Double )
DoubleValue = aiOSFont.Leading

Supported on Mobile (iOS).

The leading for the font. The leading is the recommended vertical distance from the bottom of the descenders to the top of the next line in a multiline setting.

Sample Code

Var f As iOSFont = iOSFont.SystemFont(20) // 20-point
Var fontLeading As Double = f.Leading