Marcel Tannich

This plugin will hide the WooCommerce “Update Cart” button and reload the quantity changes dynamic over jQuery. You don’t need this extra click anymore!
This Plugin is based on a posting on StackExchange related to WordPress developers. I modified the basic concept and created a plugin out of it that WordPress users with less experience in PHP can integrate this function easily without destroying their functions.php file.
There are no options. Just activate the plugin and it will works.
<h3>Plugin Requirements</h3>
<ul>
<li>This plugin requires WordPress 4.9 or greater</li>
<li>This plugin requires WooCommerce 3.0.0</li>
<li>This plugin requires PHP 5.6 or greater</li>
</ul>

Dynamic Cart Quantity for WooCommerce

wpgear

The plugin makes it possible to sell Products as whole or in parts: 0.5 1.5 etc. 
(Piece of Product). Min, Max, Step & Default preset Quantity. Variable Products Supported.
For example: 
 Pizza. You can sell 1.5 Pizzas, or a quarter. With the price set for 1 piece. 
 Liquids on tap. For example, Kerosene or Olive Oil. You can sell 1.5 liters, with the price set for 1 liter. 
 Bulk materials. For example, Tobacco or Golden Sand. You can sell 0.1 g at a price quoted for 1 g.
<h4>Futured</h4>
<ul>
<li>You can set the Minimum product Quantity for all Products by default (preset = 1). But at the same time, each Product / Categories can have its own Minimum Quantity value.</li>
<li>You can set the Step of Changing the Quantity of goods for all Products by default (preset = 1). But at the same time, each Product / Categories can have its own value for the Change in Quantity Step.</li>
<li>You can set the Default – Choice product quantity for all Products by default (preset = 1). But at the same time, each Product / Categories can have its own Default – Choice Quantity value. </li>
<li>You can set the Maximum product Quantity for all Products by default. But at the same time, each Product / Categories can have its own Maximum Quantity value.</li>
<li>Works correctly with Variable Products.</li>
<li>Auto correction “No valid value” customer enters to nearest valid value.</li>
<li>Auto correction considering with “Maximum allowed for Product”.</li>
<li>Column “Quantity” on Products List.</li>
<li>Update Cart Automatically on Quantity Change (AJAX Cart Update)</li>
<li>You can set a “Value Label” for each individual Item. Individually or as a whole for the Category. For example: “Price per Meter”, “Price per Liter”.</li>
<li>It is possible to use Product – JS Object for Ext.Integration: QNT_Data. Function: WDPQ_Get_QuantityData (Product_ID).</li>
<li>Works with WooCommerce specifics from v3.4.8 & more</li>
<li>
Buttons: +/- To select the Quantity on the Product page and in the Cart.
<a href="http://wpgear.xyz/decimal-product-quantity-woo-pro/" rel="nofollow ugc">PRO Version</a> Features:
</li>
<li>You can set separate Minimum Product Quantity, Step of Changing the Quantity & Default preset Quantity – for each Variable Product Variation.</li>
<li>You can create RSS Feed for WooCommerce. Support: “Google Merchant Center” (Product data specification) for “Price_Unit_Label” -> [unit_pricing_measure], separate hierarchy Categories -> Products.</li>
</ul>

Decimal Product Quantity for WooCommerce

Products like: Pizza, Liquid on the filling, Custom weight, etc. (Piece of Product). Min, Max, Step & Default preset Quantity. Variable Supported.

Dynamic Cart Quantity for WooCommerce vs Decimal Product Quantity for WooCommerce