The length of the latus rectum for an ellipse is given by the formula:
\[
\frac{2b^2}{a}
\]
where \(a\) is the semi-major axis and \(b\) is the semi-minor axis. Here, \(a^2 = 16\) and \(b^2 = 9\), so \(a = 4\) and \(b = 3\).
Substituting these values into the formula gives:
\[
\frac{2 \times 9}{4} = 4.5
\]