He told SFX that the new series length was perfect for the storyline he had planned for the upcoming fourth series.
"It’s not a Lost-type story, full of mystery, and it’s not particularly complicated - it’s more linear," he said. "Ten parts just gives us a chance to move it on to the international stage where it takes place."
The writer promised that the new episodes will take place on a wider scale than previous series.
"The vast majority’s going to take place in America - and other countries as well - so it's got a size to it. It’s a proper, big, global ten-hour thriller," he teased.
Davies also confessed that he felt the conclusion of previous five-part miniseries Torchwood: Children of Earth had been "rushed".
"Children Of Earth could have run for ten episodes," he said. "Once you get martial law declared, we could have done three more episodes of that."
The former Doctor Who showrunner previously admitted that it was "excting" to be filming a new series of Torchwood in the US.