What is the correct romanization of イー?

Question

According to the rules of Hepburn (http://www.halcat.com/roomazi/doc/hep3.html), しいたけ is correctly romanized as shiitake. What is the correct romanization of イー as in シート? Should it be shiito or shīto or shi-to?

Answer 1

Of course it depends what romanization system you use, but generally (e.g. Hepburn) one romanizes double /i/ as ii, e.g. しいたけ → shiitake.

However, a vowel lengthened with the 長音 「ー」 (usually in loanwords) is romanized differently:

• Hepburn
  a macron over the vowel before it, e.g. シート → shīto
  (See Kenkyūsha's New Japanese-English Dictionary for modified Hepburn)

• Kunrei-shiki
  a circumflex over the vowel before it, e.g. シート → sîto

• Wāpuro rōmaji (or wa-puro ro-maji)
  a hyphen after the vowel, just as is typed, e.g. シート → si-to
  _{N.B. In other systems the hyphen may be inserted for readability.}