Customer Shipping cost not accurate

[numnumsforkids]

I just set up my Shopify. I am using USPS and UPS. My product is relatively light and I have a set box size 8x8x8 inches as my default. This easily fits 5 light items inside. However, no matter if I select one item or 10 items Shopify in the cart is showing only one cost $4.90 for USPS when clearly that would not from my experience shipping with other 3rd party carriers be only 4.90. 

I need shipping to be accurate esp since sometimes customers other 10 items and I have to either use two box (two shipping labels) or get a larger box. 

[shahrozbabar5]

Your shipping shows $4.90 because Shopify treats the order as one package by default, regardless of quantity. It doesn’t support multiple box calculations unless you use a third-party app.

Fix:

1. Set accurate product weights in each product listing.

2. Use real-time carrier rates under Settings > Shipping and Delivery.

3. Add an app like Boxify or Advanced Shipping Rules to handle:

   • Multi-box shipping

   • Per-item or per-weight logic

   • Accurate USPS/UPS rate calculation

Without one of these apps, Shopify will undercharge on multi-item orders.

Let me know if you want me to setup or further guide

[Jagruti_Naveen]

Hi @numnumsforkids !

From what you’ve described, there are a couple of reasons why the shipping cost might not be changing even when more items are added to the cart.

• First, USPS typically calculates rates based on weight brackets. Since your products are light, it’s possible that even with 10 items, the total weight is still falling into the same bracket, so the rate stays the same.
• Another thing to consider is volumetric weight. An 8×8×8 box has a volumetric weight of about 4 lbs, which might be higher than the combined actual weight of your items. In that case, the volumetric weight will be used to calculate shipping, which could explain why the rate is stuck at $4.90. That said, based on your own shipping experience, you’re probably right that the real-world cost for using a box of that size should be higher than what’s showing at checkout.

If you want accurate rates, it might help to use a setup that allows you to define custom box dimensions and considers both weight and volume when calculating shipping. The PH Multi Carrier Shipping Label app does exactly that, it supports multiple carriers including - USPS and UPS, and helps ensure your checkout rates reflect the actual cost of shipping based on how the order would be packed.

Hope this clears things up a bit!

[Channelwill]

Hi @numnumsforkids,

This is a common issue when Shopify uses a flat box size or default rate without accounting for the actual quantity or weight of items in the cart.

From what you described, it sounds like Shopify is treating your shipments as a single-package rate, no matter how many items are added, which is why you're still seeing $4.9 even for orders that should require a larger box or multiple labels.

Here are a few things you can try:

1. Double-check your shipping profile settings

• Make sure your products have accurate weights assigned.

• Consider using weight-based tiers or carrier-calculated rates with package dimensions that scale based on order size.

• Some merchants set up multiple shipping profiles (e.g. small, medium, large orders) to offer more accurate pricing.

2. Consider a shipping app for more control

If you’re frequently dealing with orders that vary a lot in size, using an app that supports smart packing (automatically calculating the number of boxes based on product dimensions) can help you avoid undercharging for shipping.

3. Keep customers informed post-checkout

Since you're using USPS and UPS, both are fully integrated with ParcelPanel Order Tracking. Even if you ship in multiple boxes, ParcelPanel will:

• Sync the tracking numbers automatically

• Display a clean, branded tracking page

• Send email updates for each part of the shipment

That way, even if the shipping cost needs adjustment later or multiple labels are used, your customers aren’t left in the dark.

Let me know if you'd like help setting it up or testing how the rates are calculated in your current setup!

If this helped, feel free to mark it as a solution so others can find it too 😊