This plugin enables setting fixed fees or calculating fees by weight and by total to all predefined shipping methods.
If you want to define and use your own shipping methods, you should manually enter shipping rates for these methods. The “Fixed rate” option allows you to define a shipping rate for each shipping method. You can manage the existing shipping methods, or add a new method if required. The “Shipping by weight and by total” option allows setting different shipping fees based on a shipment weight and total.
Please find more information about how to install plugins here.
The plugin is provided absolutely for free and includes source code.