Click here for an interactive Excel spreadsheet for water use calculations.  (Use your browser's "BACK" button to return to this page if you need to.  You need not save changes to the spreadsheet when leaving.)

If you don't have Microsoft Excel, or simply want a bit more of a mathematical challenge, you can use the formulas below for these same calculations.

Calculating annual acre feet (AF) pumped

The easiest way to calculate total acre feet used in a year is to multiply the gallons per minute rate you pumped the well, times the number of hours the well was pumped for the year, times the numerical factor .0001841.

The Formula is:   (RATE) X (HOURS) X (.0001841)

Example:   (600 gpm) X (1500 Hours) X (.0001841) = 165.7 AF per year.

The long way to calculate this is to convert gallons per minute (GPM) to gallons per hour (GPH) by multiplying GPM times 60, then multiplying GPH times hours pumped for the year, and finally dividing by 325,851 (number of gallons in an AF)

The Formula is:   (GPM) X (60) X (HOURS) / 325,851       (remember: do all multiplication first, then the division)

Example:   (600 GPM) X (60) X (1500) / 325,851 = 165.7 AF per year.

Figuring HOURS to pump a known amount of water at a known rate of diversion:

The question would be posed: "How many hours will it take me to pump 200 AF at 600 GPM?"

The Formula is:   TOTAL GALLONS / GALLONS PER HOUR

Example:   65,170,200 / 36,000 = 1,810 hours

The trick to this calculation is converting AF into GALLONS, and GPM into GPH. Remember that 1 AF = 325,851 Gal, so 200 AF = 200 X 325,851, or 65,170,200 GAL.  Also, 600 GPM = 600 X 60, or 36,000 GPH.

Some conversions for water are: