How long should a mission statement be

Consider the following mission statements:

Coca - Cola: "The Coca-Cola Promise: The Coca-Cola Company exists to benefit and refresh everyone it touches. The basic proposition of our business is simple, solid, and timeless. When we bring refreshment, value, joy and fun to our stakeholders, then we successfully nurture and protect our brands, particularly Coca-Cola. That is the key to fulfilling our ultimate obligation to provide consistently attractive returns to the owners of our business."

Mahatma Ghandi:
'Let the first act of every morning be to make the following resolve for the day:
I shall not fear anyone on earth.
I shall fear only God.
I shall not bear ill toward anyone.
I shall not submit to injustice from anyone.
I shall conquer untruth by truth.
And in resisting untruth, I shall put up with all suffering'

A mission statement is different from a company jingle or catch phrase, and should encompass your value propositions, your ideals, and your goals.

Thank you - I have seen a range from one or two sentences up to 3 short paragraphs. Your answer helped a lot!