My understanding is that the "weight" field in products does not actually "mean" anything. If you want it to mean pounds, then be consistent . . . if you want it to mean "kilograms", then again, be consistent.

That said, I was testing my Fedex that I just setup, and it seems the rates are absurdly high. That made me wonder how Fedex is calculating the rate? Presumably it uses the "weight" field . . . what about dimensions? How (if at all) does it calculate that info?

Just trying to figure it out to see if this will suffice or if I will need to get an extension.

5 Answers 5


FedEx does use the weight field for calculations.

It does not take into account dimensions, there is no support for this in standard magento.

Weight is hardcoded to lbs, the FedEx implementation is pretty much US specific.

The implementation of FedEx does not take into account various factors that are important to get accurate shipping rates, if you need more accuracy you need an extension or to write an implementation yourself.

For many people tho the FedEx in magento does suffice. The dimensional part only comes into play if you have items that are dimensionally large. If you speak with your FedEx rep (or UPS if you are with them) they will be able to advise.


Given FedEx (1/1/15 and UPS (12/29/14) are moving to dimensional shipping rate calculation for all shipping methods, the above answer doesn't apply for 2015. What are people doing to handle this with their Magento sites?

We sell relatively light items and it looks like the cost increase can be significant - a 12x12x18 box that is weighs 12 lbs will have a dimensional weight of 19 lbs based upon the FedEx calculator (http://www.fedex.com/fr_english/tools/dimweight.html).


You may be interested in checking out our new extension, which fully supports your item dimensions and dimensional rates: http://www.magentocommerce.com/magento-connect/auctioninc-shipping-calculator.html


FedEx uses both weight as well as dimensions. They will charge the higher of 2 scenarios

The example in a previous post suggested a 12 lbs. box with 12x12x18 dimensions. barring any special negotiated rates: FedEx will use (12x12x18/166)=15.61 (round up to 16 lbs.) for air shipments. FedEx will use (12x12x18/194)=13.36 (round up to 14 lbs.) for ground shipments. I can all but guarantee that Amazon has a seriously more favorable factor (in other words much better than /166 or /184.

The trouble with FedEx module on Magento is, that it will be super accurate through 5 or 6 cartons in the shopping cart, but if there are more (lets say 20 boxes) shipping ground.. that is where it all falls apart...

When you have that many boxes, your account will likely calculate freight using FedEx's multiweight (it is a big discount). Magento on the other hand, would take every individual box, calculate the dimensional weight and just keep adding them all up (ignoring your multiweight discount)...

The result is one furious online customer who 100% will abandon the shopping cart.

We had FedEx IT support tell us they could see the multiweight results being calculated on the Magento backend, while displaying a very high dollar amount on the front end (shopping cart)

If anyone has a solution for that... please DO share...

Best !!


I would like to point-out as well that the Fedex built-in extension compute rates based only on 1 single package, completely ignoring the calculated number of boxes.

See, https://github.com/OpenMage/magento-mirror/blob/magento-1.9/app/code/core/Mage/Usa/Model/Shipping/Carrier/Fedex.php#L365

And https://github.com/OpenMage/magento-mirror/blob/magento-1.9/app/code/core/Mage/Shipping/Model/Carrier/Abstract.php#L493

For example, if you have a 700 lbs shipment of items. The estimate will divide the total weight by the maximum package weight - i.e. 150 lbs for Fedex - providing you with 5 packages.

The Magento Core code then takes the 700 lbs and calculate an average of 140 lbs per package.

Finally, Fedex make the estimate request based on a single package of 140 lbs ONLY. So you are off by 560 lbs and 4 packages.

To summarize, anybody shipping things that go beyond 150 lbs with Fedex on Magento 1 touches a nice rebate.

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