The iOS Keyboard is very complex but one of the most important elements of iOS.
See also: UIPeripheralHostView, UIKeyboardImpl.
These are approximate measurements in pixels.
Maybe it should be measured in points?
Portait (iPhone, default English US keyboard)
|Space between 2 keycaps||7.5|
|Space between left edge of screen and Q||7.5|
|Space between shift and Z||7.5|
|Space between delete and M||7.5|
|Space from left edge to A||11.3|
|Space from right edge to L||11.3|
|Space from top edge to first row||7.5|
|Space from bottom edge to last row||2|
Landscape (iPhone, default English US keyboard)
|Keyboard||480 (3" devices) or 568 (4" devices)||162|