To find out how many milliliters are in 1 gallon, we can start with the conversions provided:
1 gallon = 4 quarts
1 quart = 946.35 milliliters
Now we can calculate the number of milliliters in 1 gallon:
\[ 1 \text{ gallon} = 4 \text{ quarts} \times 946.35 \text{ mL/quart} = 3785.4 \text{ mL} \]
Therefore, the answer is:
3785.4 mL