That depends on the type material you are referring to. Also, these are two different types of measurements. Gallons is a measure of volume but the other is weight or mass. Please edit your question to include more context or details.
300 US gallons = 1135 liters = 1135 kilograms = 2502 pounds. 300 UK gallons = 1363 litres = 1363 kilograms = 3005 pounds.
Since a gallon is a unit of volume, and a pound is a unit of weight, which is mass times gravity, it depends on the density (mass divided by volume) of what you're measuring. For example, 300 gallons of oil weighs a lot less than 300 gallons of water.
Nothing can weigh in gallons . 300 gallons of diesel is weighed in pounds or Kilos, and is about 7.0 pounds per US Gallon, - DEPENDING on temperature and SPECIFIC GRAVITY of that diesel fuel. - So ultimately 300 gallons of diesel will weigh between 2,070 and 2,160 pounds.
2400 pounds
300 gallons is 76,800 tablespoons.
300 gallons
300 liters = 65.99 imperial gallons
300 US gallons = 1.14 (1.13562354) kiloliters.
300 Cubic Centimeters = 0.07925161579118878 Gallons
300 liters = 79.25 US gallons = 65.99 imperial gallons
300 cubic feet = 2,244.156 gallons (rounded)
42 gallons of water is 350.7 pounds