Turfgrass Irrigation Calculator
The Turfgrass Irrigation Calculator is meant to be a tool for home owners to estimate the irrigation requirements for their lawns in Missoula. This calculator uses estimated evapotranspiration (ET) rates for a typical turfgrass as well as historical climactic data for our region. This calculator is does not integrate current environmental conditions (temperature, wind, precipitation, RH) in the calculations. This resource is meant to help guide irrigation decisions; but attention to environmental conditions, site specific soil types, as well as plant growth and development will be critical for establishing and maintaining a healthy lawn.
To use Turfgrass Irrigation Calculator:
Step 1: Select current month from drop down menu
Step 2: Select mowing height of grass (typically 2-3” for Kentucky bluegrass lawn)
Step 3: Select number of days between irrigation cycles (generally 3, but 2 during hot and dry cycles)
Step 4: Estimate or Measure Sprinkler Precipitation Rate (PPT) or the output of your irrigation system per hour
Estimate PPT:
Step 4a: Measure distance between sprinkler heads (in ground system)
Step 4b: Measure distance between rows of sprinklers
Step 4c: Select geometric design of sprinkler system
Measure PPT:
Step 4a’: Place 10 equal size containers (tin can) randomly throughout irrigation zone
Step 4b’: Run irrigation for 15 minutes
Step 4c’: Consolidate collected irrigation water into one container
Step 4d’: Measure depth of water in container (in inches) and divide by 10 to get average output per zone
Step 4e’: Multiply above (output) by 4 to get Sprinkler Precipitation Rate (inches/hour) and record in calculator table
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Step 5: Click the “Calculate” button to calculate duration required
Step 6: Repeat for each zone
Month | ||
Mowing Height (3, 2, 1") | inches | |
Days between irrigation events | days | |
Distance between heads | feet | |
Distance between rows | feet | |
Distribution volume of full circle Sprinkler Heads in GPM (if half circle than multiply by two, quarter circle multiply by 4) | GPM | |
Geometric deisgn of irrigation system | shape | |
Sprinkler Precipitation rate (enter value if measured or leave blank if using calculated estimate above) | ppt (inches/hour) | |
Irrigation Rate Calculate | minutes |