New Mexico State University
Climate Center's

Grass Water Usage Calculator
JavaScript Version

This system helps you determine either the cost of maintaining your grass per month, or the area of grass that you can support with your desired cost. It should be fairly simple, and straightforward. We have made every effort to ensure that this page is user-friendly, however if you do have a problem or a simple question you can contact me at webmaster@weather.nmsu.edu.

Step 1: Enter your cost of water per 1000 gallons without the dollar sign.  This amount should be located somewhere on your water bill.

Step 2: Select whether you are giving the monthly water bill you desire, or the square feet of grass that you desire.  Then enter that information in the box.

Step 3: Insert the average water use of your desired grass, this can be found through our PET Calculator: for Warm Season Grasses, and for Cool Season Grasses.   You should follow the directions given on that page, using August or July climate data.  Once you have that information, you can either scroll through the "ET in/mm" and locate the highest value here, enter that and select: "Maximum Daily ET", or you can subtract the first "Cum ET in/mm" from the last, enter that, and select "Monthly ET".

Step 4: Press Calculate.  Displayed on the output, will be the square feet your desired water bill will support, or the cost of watering your selected area of grass.  Output displayed for cost is in dollars, and output for area is in square feet.  If the estimate is more costly than you're willing to pay, or doesn't support enough grass, then we can suggest, that you can water it less.  While this will produce less quality grass, you will still have a fairly large patch of grass.   You can estimate this, by returning to Step 3, and selecting a lower water usage level for your grass.  If all else fails, you can also completely cut out some grass from being watered, thus reducing the area of your grass.