Question: how to calculate water volume in a spa?
Answer: Now divide the number of seconds it took to fill your hot tub, by the number of seconds it took to fill the one gallon bucket, and you will have the approximate water volume! For example: You filled your hot tub in 30 minutes (1800 seconds) and filled the one gallon bucket in 6 seconds. 1800 divided by 6 = 300 gallons.