Checkout Imager::Font::Wrap. Might save some time.

Imager::Font will return the size you're looking for with this snippet (from cpan)

  $blue = Imager::Color->new("#0000FF");
  $font = Imager::Font->new(file  => 'pathtofont.ttf',
                            color => $blue,
                            size  => 30);

  ($neg_width,
   $global_descent,
   $pos_width,
   $global_ascent,
   $descent,
   $ascent) = $font->bounding_box(string=>"Foo");
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