Does the shipping calculator display the total shipping, or just the current product?
The WooCommerce Shipping Calculator plugin lets you show the shipping calculator on the product page so that customers can check the cost before adding a product to their cart.
If there are no products already in the cart, then the shipping calculator on the product page will show the cost for the current product only. Alternatively, if there are already products in the cart, then the calculator will show the total cost based on the current cart contents plus the product on the current page.
This gives customers the most accurate indication of what the shipping cost will be, based in the information which is available at that stage.
Depending on your shipping settings, it is possible that the shipping cost will increase as the customer continues adding bigger quantities and products to their cart. This will be clearly shown on the checkout, and also the cart if you are displaying the shipping calculator on the cart page.