To convert quarts to gallons, you can use the conversion factor that 1 gallon is equal to 4 quarts.
So, to convert 12 quarts to gallons:
\[ \text{Gallons} = \frac{\text{Quarts}}{4} = \frac{12 \text{ quarts}}{4} = 3 \text{ gallons} \]
Therefore, the correct answer is 3 gallons.