First off, I would like to thank youtuber Matt123Spi Sales for the information in this post, as he has carried out the work to give a reasonable sample of what to expect from Steam Siege booster boxes.

The link to his video is below.

When buying a box of Pokemon booster packs, it is good to know what to expect from each box when you open 36 packs.

In this post I will explain how many Break, EX, full art, holo, or secret rare cards you can expect (on average) when purchasing a steam siege booster box.

From the work carried out by Matt below you can expect at least 2 to 3 break cards, 2 to 3 EX cards, two full art cards, 7 to 8 holo cards, and a secret rare in every one out of three boxes.

That is an average of 14 great cards. That is not including the rare, uncommon or common cards you will always find in each pack. In every pack, you will receive at least one rare card.

Please note that this was carried out on a sample size of 24 booster boxes 48 blister packs and one elite Trainer Pack. While this is an indication of what you may expect, there are no guarantees that you will get better or worse Pulls from any box you purchase.

The total amount of booster but it were opened in this sample is 1016.

While this is a fair sample size, it is still a smallest sample size compared to some scientific test that may be carried out from time to time.
Good luck with your booster box.

Link: Steam Siege booster box pull rates