magnitude
noun(mag-ni-tude)
a number assigned to the ratio of two quantities; two quantities are of the same order of magnitude if one is less than 10 times as large as the other; the number of magnitudes that the quantities differ is specified to within a power of 10
Synonyms: order of magnitude, 
magnitude
noun(mag-ni-tude)
relative importance
Examples:
A problem of the first magnitude. 
magnitude
noun(mag-ni-tude)
the property of relative size or extent (whether large or small)
Examples:
They tried to predict the magnitude of the explosion. 
About the magnitude of a small pea.