Add Google Analytics Ecommerce tracking to a donation form created through Gravity Forms.

gravity_forms_ga_tracking.php

<?php
/*
 * Add custom query vars to handle Google Analytics Ecommerce tracking.
 * This should be placed in a plugin or in functions.php of the theme.
 *
 * You'll want to use the redirect method for Gravity Forms confirmations and 
 * turn on passing field data via a query string.  An example we used was:
 * donation_amount={Donation Amount:13}&donation_id={entry_id}&donation_recurring=0
 */
function sm_add_query_vars( $vars ){
  $vars[] = "donation_amount";
  $vars[] = "donation_id";
  $vars[] = "donation_recurring";
  
  return $vars;
}
add_filter( 'query_vars', 'sm_add_query_vars' );

//Place the following directly into the page template used for your donation thank you page.
//Track donation through Google Analytics Ecommerce Tracking
$donation_amount = get_query_var( 'donation_amount' );
if( $donation_amount != '' ): //Only do Ecommerce if the donation amount is in query vars
  
  //Donation Amount
  $donation_amount = filter_var( $donation_amount, FILTER_SANITIZE_NUMBER_FLOAT, FILTER_FLAG_ALLOW_FRACTION );
  $donation_amount = number_format( $donation_amount, 2, '.', '' );

  //Gravity Forms Transaction ID
  $donation_id = get_query_var( 'donation_id' );
  $donation_id = intval( $donation_id );

  //Whether Donation is Recurring or One-Time
  $donation_recurring = get_query_var( 'donation_recurring' );
  $donation_recurring = intval( $donation_recurring );
  $donation_recurring_sku = ( $donation_recurring == 1 ) ? 'RD' : 'OTD';
  $donation_recurring = ( $donation_recurring == 1 ) ? 'Recurring Donation' : 'One-Time Donation';

?>

  <script type="text/javascript">
  
    _gaq.push(['_addTrans',
      '<?php echo $donation_id; ?>',                // transaction ID
      '',                                           // affiliation
      '<?php echo $donation_amount; ?>',            // total
      '',                                           // tax
      '',                                           // shipping
      '',                                           // city
      '',                                           // state or province
      ''                                            // country
   ]);
   _gaq.push(['_addItem',
      '<?php echo $donation_id; ?>',                // transaction ID - necessary to associate item with transaction
      '<?php echo $donation_recurring_sku; ?>',     // SKU/code - required
      '<?php echo $donation_recurring; ?>',         // product name
      '',                                           // category or variation
      '<?php echo $donation_amount; ?>',            // unit price - required
      '1'                                           // quantity - required
   ]);
   _gaq.push(['_trackTrans']);
  
  </script>
      
<?php endif; //End Google Analytics Ecommerce Tracking ?>