Gallon (US)

Definition:In both the US customary and imperial systems of measurement, a gallon is a unit of volume specifically for liquid capacity. 231 cubic inches are regarded as one US gallon (3.785 liters). The imperial gallon, on the other hand, is defined as 4.54609 liters and is used in the UK, Canada, and several Caribbean countries. The gallon is divided into four quarts in both systems. After that, quarts are split into two pints, and pints are split into two cups. One gallon equals four quarts, eight pints, sixteen cups, or thirty-two gills because a cup is made up of two gills. The US gallon and the imperial gallon are further distinguished by the fact that the former is divided into four fluid ounces and the latter into five.A US fluid ounce is therefore 1/128 of a US gallon while an imperial fluid ounce is 1/160 of an imperial gallon.
Quart

Definition: In both the imperial and customary measurement systems used in the United States, the quart (symbol: qt) is a unit of volume. There are various quart definitions. A liquid quart in the US is roughly equivalent to 0.946353 liters, while a dry quart is roughly equivalent to 1.101221 liters. The imperial quart is equivalent to 1.136523 in the UK. The quart is a quarter of a gallon in both the US and the UK.

To convert a gallon measurement to a quart measurement, multiply the volume by the conversion ratio.
So how to  Convert Gallons to Quarts :

Since one gallon is equal to 4 quarts, you can use this simple formula to convert:

quarts = gallons × 4

The volume in quarts is equal to the gallons multiplied by 4.
anyway if you want to convert gallons to quarts a huge number you should use:
https://www.calculatorful.com/gallons-to-quarts