# What is magnitude?

And I read somewhere that temperature is a scalar quantity with magnitude.
But in the thread above, a poster said that a magnitude is always zero or positive.
But then again... temperature can also be negative.
So, how can temperature be a scalar quantity and have a magnitude if it's -30F?

## Answers and Replies

Doc Al
Mentor
In general, a scalar is a quantity that can be represented by a single number with units (no direction). It can certainly be negative.

The magnitude of a vector is the length of the vector, which can only be positive.

Temperature can only be negative if you use a useless unit of measure, anyway.

You can not have negative kelvins because the kelvin scale makes sense. The celsius scale works, but its values are based on something subjective that humans decided and not something with any real physical meaning.