How many gallons of water are in my pond that measures 18'x7'x 3'?

Answer 1

It's unlikely that your pond has vertical sides and is 3' deep everywhere, but if it were, it would hold 18 * 7 * 3 = 378 cu. ft. of water. Converting the dimensions to metric at the start makes everything easier. 378 * (12^3) * (2.54^3) give you the number of cc's, dividing that by 1000 gives you the number of liters (10703). Dividing THAT by 3.7854 (liters/gallon) gives you about 2828 gallons. A typical pond, however, probably slopes from very shallow at the periphery to maximum depth near the center. This means it likely holds 30 - 40% less than if it had steep vertical sides and a consistent depth (like a typical above-ground pool). Your pond is probably on the order of 1500 - 1900 gallons.