To give another angle on the explanation of this: the reason why the pronunciation of this word gets confused by English speakers is that English doesn't have "contrastive consonant doubling", whereas Japanese does. In other words, a word romanized as "boken" and one romanized as "bokken", apart from being pronounced differently, can never be the same word, because a single k and a double k are different.
In English, although "matter" is spelled with two t's and "crater" is spelled with one, the pronunciation of the "t" sound is exactly the same in both. In other words, the spelling is a historical artifact which is unrelated to the phonology (at least in modern English) of these words. It may have been the case at an earlier stage in English that the pronunciation of "t" and "tt" were different, but no longer.
Zoli Elo wrote:
I thought that to romanji was bokuto... Learn something new...
Japanese also has contrastive vowel
So the "o" sound in this "to" is a long one, which is often romanized as "ou". Unfortunately, the way words are usually romanized, there's often no way to know which vowels are long and which are short unless you know the language.