Tenor guitars and baritone ukuleles have many similar features, including a short scale, four strings and a parlor-sized guitar-shaped body. If you have an instrument fitting that description, but aren't sure which it is, take a close look at it from top to bottom and compare the basic features of tenor guitars and baritone ukuleles.
Measure the length of the instrument's neck. If it is 21 to 23 inches long, it is a tenor guitar. If it is 18 to 20 1/4 inches, it is a baritone ukulele.
Assess the overall length of the instrument. If it is more than 31 inches, it is a tenor guitar. If it is 29 to 31 inches, it is a baritone ukulele.
Evaluate the width of the neck. If it is as thin as a banjo neck, it's a tenor guitar. If it's wider than a banjo's neck, it's a baritone ukulele.
Compare the headstock to the headstock of a banjo. If they look similar, it is a tenor guitar.
Check the tuners to see if they are for nylon strings or steel strings. If they are for nylon, it's a baritone ukulele. If they're for steel, it's a tenor guitar.
Look at the anchor. If it has a tailpiece string anchor, it is a tenor guitar. If it has a bridge anchor, it's a baritone ukulele.
Inspect the frets close to the nut for the wear that steel tenor guitar strings can cause. If the frets seem worn down, it's a tenor guitar. If not, it may be a baritone ukulele, but you can't rule out a newer tenor.
See if the bridge and tailpiece can move. If so, it is a tenor guitar. Luthiers used to make tenors this way to compensate for the pressure steel strings can exert.
Banjo players used tenor guitars as crossover instruments when they first came out, so tenor guitars came with some banjo-like features. If your instrument's neck is less than 18 inches long, you're probably looking at a tenor ukulele or a custom instrument.
Don't string your instrument until you know what it is, because putting tenor guitar strings on a baritone ukulele can damage the instrument.