Fifths can be perfect, augmented or diminished. Below you can see that the number of steps determines the quality of the interval:
Perfect fifth, 3 1/2 whole steps or 7 half steps:

Augmented fifth, 4 whole steps or 8 half steps:

Diminished fifth, 3 whole steps or 6 half steps:

When analyzing the quality of a fifth we should know that:
If there are accidentals you should identify the interval without accidentals and then analyze the effect of the accidentals.
Example: D-A#:

Another example: G-Db:

Identifying fifths by counting whole and half steps is slow and confusing.
See I > Intervals for related entries. To learn about go to Tutorials > Intervals.