I read somewhere online that the New Gods are actually giants and that the boom tubes are what allow them to enter the main dc universe as normal sized beings is this true?

Yes, it is.

It varies. Devilance from 52 seemed to be in the general range as Galactus. Supergirl once traveled to Apokolips without a boom tube and she was pretty much the size of Darkseid's finger, which should put them a bit above Galactus.
 
On the other hand, in New Gods vol three, S'ivaa tears a hole between the fourth world and our universe, and New Gods were big enough to be able to hold the Earth in the palms of their hands, putting them far above Galactus, or Celestials, or just about any other corporeal entity in DC or Marvel.

" To add to my original question, how much more powerfull are they in their true forms? "

Another question given what the New Gods are, shouldn't they be more powerfull then they are usually portrayed?

" Another question given what the New Gods are, shouldn't they be more powerfull then they are usually portrayed? "

" @AtPhantom: So in the DC/Marvel cross over The Hunger, Orion and Darkseid should have easily won against the Surfer and Galactus? "

" It varies. Devilance from 52 seemed to be in the general range as Galactus. Supergirl once traveled to Apokolips without a boom tube and she was pretty much the size of Darkseid's finger, which should put them a bit above Galactus.  On the other hand, in New Gods vol three, S'ivaa tears a hole between the fourth world and our universe, and New Gods were big enough to be able to hold the Earth in the palms of their hands, putting them far above Galactus, or Celestials, or just about any other corporeal entity in DC or Marvel. "

"interesting... so technically the physical strength of a New God should excel Superman several million times over since technically the strength of the New Gods is measure of them at there human scale size... so if they are several million times larger in size... shouldnt there strength increase at that level as well ?  "

" @AtPhantom: What about Orion I can see Darkseid losing galactus but Orion losing to the Surfer "

Seeing how the New Gods are so many times larger than Humans, Kyrptonians and most other beings for that matter, how is it only a few match or exceed Superman in pure strength?

" Seeing how the New Gods are so many times larger than humans and Superman himself and most beings for that matter, how is it only a few match or exceed Superman in pure strength? "

The way I see it, the gods are that large in their dimension, yet they cannot cross over to Earth without a boom tube because it's on a different plane of existence.

Interesting didn't know this.

Oh, so that's why Gog was so damn big in Thy Kingdom Come.

I see.