Query the metrics for the text and dump the results on the screen.
<?php
/* Create a new Imagick object */
$im = new Imagick();
/* Create an ImagickDraw object */
$draw = new ImagickDraw();
/* Set the font */
$draw->setFont('/path/to/font.ttf');
/* Dump the font metrics, autodetect multiline */
var_dump($im->queryFontMetrics($draw, "Hello World!"));
?>