This is an accepted solution.
There's a couple of ways you can approach this. If you're using manual rates, you can configure them in a way that ordering multiple units of an item sees the shipping rate increase each time. I'll detail an example below.
Let's say you have a product that weights 2.5lbs, and you want to charge $5 shipping for each unit a customer orders. You can set a shipping rate with a weight range of 0lbs-2.5lbs with a cost of $5, which will apply if the customer orders one unit of the item. Your next weight range can be 2.51lbs-5lbs, with a cost of $10, meaning if the customer orders two units of the item the weight of the products will be 5lbs (2.5lbs x 2) and the $10 rate will apply. You can create multiple shipping rates in this manner on an increasing scale, which will result in the customer paying a higher price of shipping as the weight of the cart increases.
This method does rely on you using manual, weight-based rates, and you'd have to consider various combinations of products and what the shipping costs will be when customers add them to their cart. Generally, it's a good idea to know what it'll cost you to ship items of various weights so you can then set your shipping rates accordingly. Please remember as well that you can set different shipping costs for different countries and regions through shipping zones, so if you do ship to various locations that have higher shipping costs you can manage that accordingly.
I'd also like to point out that you're able to set different shipping rules for different products using shipping profiles. You may wish to charge more or less for the shipment of various items, and shipping profiles provides you with the chance to do that.
Finally, you can also read about setting an effective shipping strategy in this article over on the Shopify Blog. Understanding how to manage your shipping is one of the more difficult things about running a business so I would recommend levering the resources Shopify provides to learn how to do so effectively.
I hope this helps but please let me know if you have further questions.
It did and did not work. I am doing the manual rates and here is what happened. I have model of kayak and it comes in 4 different colors, it worked just fine when I put 2 of the same color in the cart but when I put a third kayak same one but different color it did not charge the shipping rate 3 times just 2. Hopefully that makes since. Each item and color under it is entered with a weight of 1 and then in shipping I have separate categories, 0-1lbs, 1-2lbs, 2-3lbs. Hopefully this makes sense.
Okay great, thanks for letting me know. I'm glad that it seems to be working for you now. You can try adding different products and quantities to your cart and proceeding to checkout to see which rates display, as a method of testing your rates. This should give you a clearer indication if they're set up correctly.