USPS Flat Rate Shipping

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I am setting up my store and after this long downtime tonight I am noticing that there are no options to calculate shipping price based on the size of items. 

I currently use Woocommerce and if someone orders items from my store, it will calculate the shipping to be priority, but as soon as it is cheaper to be medium flat rate box worthy and it fits into that box, it will populate tat price.

Any help?


First of all...welcome to Shopify!! We developed for a competing platform for about 6 years, and the difference in all-around quality is amazing. You'll also find some lovely communities that are very active and happy to help each other out. My personal favourite is the Shopify Entrepreneurs group on Facebook. 

Shopify’s standard shipping calculation options are quite basic, which is where third-party shipping calculation apps will come into play.

Our app, Intuitive Shipping, does exactly what you are looking to do. Our smart boxing algorithm will determine the best size, weight, and number of boxes required for an order so that your customers are offered the cheapest shipping price (you can also have options like express and priority for customers who want their order faster). This also means that your shipping costs you’re charging your customers are accurate so you aren’t hit with unexpected shipping costs when you go to fulfill an order. We also have a ton of other features, so there may be some things that will help you with your shipping that you haven’t thought of yet.

With any third-party shipping calculation app on Shopify, you’ll need to get the Carrier Calculated Rates feature through Shopify, which is $20/month a-la-carte, or free if you switch to annual billing. Since you’re switching from Woo, I would imagine you know you have a great business that will be around for years to come, so switching to annual billing is likely the best option. You can contact Shopify directly to get this added. 

Please reach out at if you have any questions - we’re happy to answer any questions and help guide you through getting set up. We also offer a free 14-day trial so you can poke around and try it in your store for free :)

Warm regards,


Co-Founder / CEO @ Intuitive Shipping
Execute a strategic approach to shipping | Intuitive Shipping | Smart Boxing | Automate Shipping Profiles
Shopify Partner
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To get pricing based on dimensions, as a first you should be able to define dimensions for each product such that these products can accommodated in boxes. Since Shopify does not have a way to allow dimensions for individual products, you can use the Multi Carrier Shipping label app for this. Once the dimensions are set, then you can define boxes. Having done with this, the app will kick in it's own algorithm and pack the items based on dimensions and weight. So if the products are deemed fit to be packed in a small flat box, then so be it. Otherwise, if Medium flat rate box is what they get packed in, then you have to pay those charges.

Product Owner @ PluginHive
Shipping Automation | FedEx shipping | Multi-carrier shipping | Shipment Tracking | Australia Post shipping