Thank you - you must be catching up because your response was quick!
Works like a charm. Here is the changed code for anyone else interested...
foreach($order->products as $k => $product){
if(!empty($product->cart_product_quantity) && !empty($product->product_weight)){
$product_weight=(float)$weightClass->convert($product->product_weight,$product->product_weight_unit,'oz');
$package_weight+=($product_weight * $product->cart_product_quantity);
if($package_weight>$maw_weight){
$messages['items_weight_over_limit'] = JText::_('ITEMS_WEIGHT_TOO_BIG_FOR_SHIPPING_METHODS');
return true;
}
}
}
That is for usps.php
I also changed the standard weight measurements to the following in system configuration(for use in the USA):
Modified for USPS plugin
Dimension symbols: in,ft,yd,m,dm,cm,mm
Weight symbols: lb,oz,ozt,kg,g,mg
Thanks again Nicolas...