I won't speculate on what that size is, but it certainly is not a size 0.
Stories that speculate on the effects on society of inventions appearing before their time (such as The Difference Engine by William Gibson and Bruce Sterling, that posited computers in the Victorian era) are certainly science fiction.
If you want me to speculate, I'd say it ran far deeper than that.
Which irked her for reasons she didn't want to speculate about.
It didn't make him feel warm and fuzzy to speculate after the lawyer's letter to Cynthia Byrne.
It is idle to speculate on the habits of this earliest of known birds.
But the most luxuriously housed has little to boast of in this respect, nor need we trouble ourselves to speculate how the human race may be at last destroyed.
A contest awhile back called for people to speculate what would be the best device to hook up to the Internet.
Men speculate about the analogy between Mars and the earth, and infer that it is inhabited, without troubling about all the planets.
Thus one of the earliest of the great military theorists lived to speculate on the tactics of the present day.