How to get product availability with product id in magento?

Question

Is it possible to get product availability by passing a product ID to the Magento system?

Answer 1

To fetch the quantity (in stock) for any given product

$model = Mage::getModel('catalog/product'); 
$_product = $model->load($product_id); 
$stocklevel = (int)Mage::getModel('cataloginventory/stock_item')
                ->loadByProduct($_product)->getQty();

Answer 2

You can get stock info (Mage_CatalogInventory_Model_Stock_Item class) by product's ID without loading whole product data (at least in Magento 1.7)

$stockItem = Mage::getModel('cataloginventory/stock_item')
               ->loadByProduct($productId);

And then you can use getQty() and other methods on $stockItem object to get required info. You can find them in the source file for the class