4 quarts of water is the same as 1 gallon of water in US measurements.

Basic conversions

  • 4 quarts = 1 gallon.
  • 1 gallon ≈ 3.8 liters (about 3.79 L).
  • So 4 quarts ≈ 3.8 liters of water.

If you’re following recipes or hydration advice online in early 2026, “drink a gallon of water a day” is effectively telling you to drink 4 quarts (about 3.8 liters).