Luggage rules for Icelandic-SAS itinerary

I don’t know the answer to your exact question but I did want to share my recent observations on some flights for Icelandair.
Leaving Seattle- somewhat strict on measuring bags in sizer. Some leeway given.
Leaving Keflavik- anything goes. People boarded the plane with multiple shopping bags plus carryons.

Each airline has their own luggage rules, and they go by their own rules. It doesn’t matter who you purchased the tickets with. You have to go with the most restrictive rules.

We flew an Iceland Air/SAS combo in July from Pdx. They weighed our carry-on bags at check in. I had to repack some of the items from my bag into my son's. Then at the gate they used the sizer. My bag was sticking out a little at the front due so I had to shuffle some items from the front pocket to another bag.

In Reykjavik and Copenhagen nobody cared.

@shannon thank you.

We flew an Iceland Air/SAS combo in July from Pdx

How were things handled on your return flight? Did SAS comment on weights or sizes?

I would offer a different opinion than what travel4fun has noted....

The baggage rules on an itinerary involving multiple airlines is decided by the
rules of the airline that you purchase your ticket from (First Marketing Carrier).

So based on the info OP has provided, SAS should honor the checked bag
allowance. The outbound part is no issue as OP has surmised; Icelandic should
tag the bag all the way to Mallorca (assuming this itinerary is all on one ticket).

With any luck, you should be able to confirm baggage fees as part of the purchase process.
And given the inexperience of airline ground staff these days, print out the documentation
and have it available at the desk when you check in for your return flight in Mallorca.

Depending on the actual aircraft, SAS, I suppose, may require you to check an oversized
carryon, or delay transporting a heavy suitcase for aircraft weight allowances, etc. But they
should not levy any additional surcharges.

https://www.icelandair.com/support/terms-and-conditions/optional-service-and-fees/#what-if-my-flight-is-operated-by-more-than-one-airline-

Did not read through this but it looks like where you should be able to find the answer

Blockquote

How were things handled on your return flight? Did SAS comment on weights or sizes?

Blockquote

In hindsight we checked on the return. But I usually check coming home as my luggage seems to grow on these trips!

I only fly to Europe once a year, I always check a bag and my carry-on tote is not large, so many folks here have a lot more experience dealing with this question than I do. However, it is my understanding that the checked-bag rules of initial operating airline apply (checked bags will not be re-examined when you change planes) but you are subject to the carry-on rules of each flight you take.

Maybe I have it wrong.