What instrument has the same range as a Tuba? I want to know because there is not a lot of tuba music so I think I should just play another more popular instruments music and maybe transpose down (or up) an octave.

It depends on the Tuba.

The Euphonium (Tenor tuba) is pitched in Bb. (Note: Tuba parts are generally *written* at concert pitch.)

The Bass Tuba is an F instrument.

The Contrabass Tuba (what you usually see played by large professional orchestras) is a CC (C below low C) instrument.

Unless you are playing a part already in the Bass (F) clef (i.e. cello, doublebass or bassoon), you'll be transposing down.

Note: The above info comes from an old (1982) book on orchestration that I own. I can't vouch for it's accuracy.