Get ratings section by product id #M2 From http://magento.stackexchange.com/questions/123568/how-to-get-rating-summary-in-magento-2

rating.php

<?php

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$reviewFactory = $objectManager->create('Magento\Review\Model\Review');

$storeId = $this->_storeManager->getStore()->getId();
$reviewFactory->getEntitySummary($product, $storeId);

$ratingSummary = $product->getRatingSummary()->getRatingSummary();