Device sizes are published as the diagonal size. Your 14 inch tablet should have a diagonal of 14 inches.
My device is published as a 10 inch tablet but the diagonal actually measures 9 5/8 inches.
The following code reports that pretty accurately.
In my case the dots per inch computed from "160 * GetDeviceLayoutValues.Scale" is reported as 320 instead of the actual which is 275.4
The density independent pixel (dip) is rounded from 275.4/160=1.72 to 2, which make dips bigger then they should be. In your case about 50% bigger.
Dim r As Reflector
r.Target = r.GetContext
r.Target = r.RunMethod("getResources")
r.Target = r.RunMethod("getDisplayMetrics")
Log(r.GetField("xdpi"))
Log(r.GetField("ydpi"))
Dim xw As Float = GetDeviceLayoutValues.Width/r.GetField("xdpi")
Dim xh As Float = GetDeviceLayoutValues.Height/r.GetField("ydpi")
Log(xw & TAB & xh & TAB & Sqrt(xw * xw + xh * xh)) 'Log: 5.787403583526611 7.716537952423096 9.645672680785086