Shipping Calculation for Multiple Items In Cart

I'm using nop 4.00

If I have one item in the cart that ships UPS (shipping enabled checked and dimensions and weight entered for the item), the rate calculates to $32.03

If I have one item in the cart that has Free Shipping Checked, the rate calculates to $0.00, and ships by USPS.  

If I have two items in the cart, one ships UPS, the other has Free Shipping checked and ships USPS, the rate calculates to $46.07.

If I have two items in the cart, one ships UPS, the other has Free Shipping checked and ships USPS, and either one or both have Ships Separately Checked, the rate calculates to $52.77.

Something seems wrong with how shipping rates are being calculated with multiple items in the cart and various shipping methods.

Any suggestions?  Is shipping calculated differently in 4.20? Any changes expected in 4.30 with regard to shipping?

Is there a Plugin that can better handle the situation described above?

"Free Shipping Checked" on product should exclude that product's weight and dimensions from being seen by the carrier API.   (It should be that way in 4.00 as well as 4.20)

I don't  recall if the UPS plugin for 4.00 has a "Tracing" option (at bottom of configure page).  If it does, then select it; then, go through checkout until you see the rates, and then get the tracing from the System > Log.   If you need help interpreting it, post it here.

Thanks for your help with the UPS tracing.  In the System Log, it looks like the UPS plugin is sending information for both items to UPS for a response.

How about the weight / dimensions - are they in the tracing?  (typically carrier rates are weight based, unless dimensional weight overrides it)

New York wrote:

Here's what's inside the Request, looks like it's passing both packages, and the one that has Free Shipping checked has the value of 0 for weight and dimensions, but somehow the Request is showing 1 for each:

<Service><Code>03</Code></Service><RateInformation><NegotiatedRatesIndicator/></RateInformation><Package><PackagingType><Code>02</Code></PackagingType><Dimensions><Length>43</Length><Width>17</Width><Height>6</Height></Dimensions><PackageWeight><Weight>12</Weight></PackageWeight><PackageServiceOptions><InsuredValue><CurrencyCode>USD</CurrencyCode><MonetaryValue>585</MonetaryValue></InsuredValue></PackageServiceOptions></Package><Package><PackagingType><Code>02</Code></PackagingType><Dimensions><Length>1</Length><Width>1</Width><Height>1</Height></Dimensions><PackageWeight><Weight>1</Weight></PackageWeight><PackageServiceOptions><InsuredValue><CurrencyCode>USD</CurrencyCode><MonetaryValue>259</MonetaryValue></InsuredValue></PackageServiceOptions></Package></Shipment></RatingServiceSelectionRequest>

RE:  "...the one that has Free Shipping checked has the value of 0 for weight and dimensions"

I don't see "value of 0".  In your tracing I see value of 1 for the second package:
<PackageWeight><Weight>12</Weight></PackageWeight
...
<PackageWeight><Weight>1</Weight></PackageWeight>

I think this is because nopCommerce will "round up" less than 1 to 1 when it calculates the package weight.  Not excluding the item completely seems like a bug in the core nopCommerce, but I'd have to dig into the code more to see for sure.  I think 'older' versions of nopC would not include the item at all, but I'm not sure if that was the case generally, or more specifically handled by 'internal' (non-carrier) rate calculation plugins in the past.  See this blog.

So, If you need the correct action now, you need to customize,  or Shipping Director can do it as per the blog  (note, it's a very old blog, and I think you may not need to even have the Packing rule in there anymore, but it can't hurt.  I'll check that later.)

I was looking at Shipping Director to solve this issue.

One question I have is would Shipping Director be able to consider items that drop-ship from another vendor?  

If there are multiple items in the cart that ship from various different warehouses, with different shipping methods, some with free shipping, will Shipping Director consider all of this when making a shipping rate calculation?

Is there a lot of configuration required to get the Shipping Director Plugin to consider these scenarios?

Shipping Director has its own Setting (at the bottom of its configuration page) for "Use Warehouse Location".  You would select that one, and un-select the core one in admin shipping settings.  Shipping Director's Packing ignores items marked FreeShipping.

Your configuration would be as easy as and similar to what was in the blog - two rules:

10
Packing
Pack ignores items marked FreeShipping
true
Packing.FirstFitSingleBox

20
OptionExit
UPS
true
Shipping.UPS

Be sure that Shipping Director is the only "Active" shipping rate provider.  (You can still configure the UPS plugin even when it's not active)

(Contact us at support at noptools.com if you have any questions)

Thanks!  I'll look into the Shipping Director plugin this week.  If I have any questions, I'll let you know.