The difference between a tuba and euphonium is that a tuba is a lower and slightly larger instrument. The tuba is a large brass wind instrument that can be played while standing or marching in a band or while sitting in an orchestra. The euphonium is also a brass wind instrument and is very similar to the tuba in its look and construction. The main difference between a tuba and euphonium is that the tuba typically covers the lowest notes when played in an ensemble, and the euphonium plays a slightly higher range of notes.
Tubas were originally developed in Germany and were used as a marching band instrument that was meant to be played while standing or marching. A change in the position of the mouthpiece allowed the tuba to be played sitting down and made it an important part of orchestral arrangements. The tuba is made in five different sizes, which all have slightly different ranges because they have tubing of different widths. Tubas generally have three or four piston or rotary valves. The purpose of the tuba in a band or orchestra is typically to play very low, staccato notes.
Euphoniums are also brass wind instruments that can be played sitting down and are usually included in a symphony orchestra. They are known for having a dark, rich tone that fills the tenor spot in the brass instruments much like the cello does for string instruments. A euphonium usually has three or four valves, much like the tuba, and has conical tubing that gradually gets bigger instead of staying the same width throughout the instrument. Euphoniums can also be compensating or non-compensating, with compensating versions having an extra tube that makes it easier to keep certain keys in tune.
A tuba and euphonium are very similar in several ways, but they also have their differences. The two instruments are members of the same family, but the tuba is the biggest member, and the euphonium is like a smaller sibling. A tuba likely plays very low notes in an arrangement, while the euphonium covers a higher range and is often played with a smoother tone and style. There may also be a difference between a tuba and euphonium for beginning players because, even though the valves and tubing of the two instruments are very similar, the intonation of a euphonium might be harder for a new player to master, and there are fewer examples of quality euphonium playing to learn from. The tuba and euphonium have both been important to band and orchestral music, but they each retain their own special sound in an arrangement.