Calculating Nozzle Inches Per Hour

post by Logisan on Oct 18, 2022

What is the formula to calculate Nozzle Inches / Hour as needs to be configured per zone? I used the yard map to measure the square footage (and added sprinkler heads into the map) and tested water flow at the water meter directly. The meter shows roughly 1 Gallon / Minute (60 Gallons / Hour) for each zone tested.

Thank you,

Norman Drews

post by championc on Oct 19, 2022

(Area in sq. Ft / Min running / Gallons used) x 60

Use a water meter with a before and after reading to get the gallons used, maybe running a test on each zone for 5 minutes

post by Logisan on Oct 19, 2022

Thank you for your response.

I think I am reading the water meter incorrectly. One complete turn is not 1 gallon. I’ll take the readings again.

post by ProWater on Oct 23, 2022

@Logisan One revolution of meter is normally ;

1 Cu ft. of H20 = 7.48 gallons

post by Logisan on Oct 23, 2022

Thank you. I watched a video and figured out how to read it correctly. For us it is measured in gallons. The formula doesn’t make sense to me though to calculate nozzles inches per hour. As an example the below will give me two different numbers and all I did was extrapolate the second one (doubled the time).

(1000 sq feet \ 5 minutes \ 50 gallons ) * 60
(1000 sq feet \ 10 minutes \ 100 gallons ) * 60

post by ProWater on Oct 23, 2022

Really, you should look in the manufactures specifications book.

However as you indicate by your meter this is fairly simple and text book. In 5 minutes you had 50 gallons, thus divided by 5 = 10 gallons a minute.

Basic Formula is:

Precipitation Rate
Pr = 96.25 x Total GPM ( 10) divide by

Total Area 1000

= .96 in./hr

post by tmcgahey on Oct 25, 2022

Spec book is a great starting point IMO, but unless the system is perfectly installed with perfect overlap, spacing, system pressure, etc., there will be variations in PR. My MP’s were pretty close to the spec sheet after some adjustments and tweaking of my zones after a catch cup test.

I also go out every 3 months or so and check/adjust nozzles to make sure I am getting the spray pattern I want.

post by Logisan on Oct 26, 2022

Unfortunately for me, everything was preinstalled with the new home, so I don’t have any specs, but I did get an accurate gallons per minute looking at the water meter. Interesting values. We’re going to layout the sprinkler heads different in our backyard (patio) at some point. Right now, it’s just St. Augustine grass - trampled by large dogs. Below are my numbers. The read is after 1 minute of water per zone.

Zone			Area		Start		End		Inches / Hour
Patio - Home (E)	1415.22		871352.5	871369.5	1.16
Patio - Home (S)	1426.97		871369.5	871381.0	0.78
Patio - Fence (W)	1291.20	871381.0	871390.6	0.72
Patio - Fence (N)	1455.40	871390.6	871400.0	0.62
Front - Flowers		257.63		871400.0	871419.2	7.17
Patio - Fence (E)	1690.10		871419.2	871421.0	0.10
Front - East | North	591.22		871421.0	871435.0	2.28
Front - West		500.42		871435.0	871459.2	4.65

post by tmcgahey on Oct 27, 2022

Boy, some of those seem off. What type of irrigation is running in these zones?

Flowers

Patio - Fence E

Front - West

post by Logisan on Oct 28, 2022

Hi. Unless the water measurement or nozzle type is wrong (it probably is), here they are. I can take the water measurements again when I get a chance.

Can you correctly tell me the type of sprinkler head these are?

Zone "Flowers"

The ‘Flowers’ zone is combination of grass and flower/shrubs but I could only select one, so I used Fixed Sprayhead.

Zone "Patio - Fence(E)"

I selected Rotor head, it rotates so I guessed it was this one.

Zone "Front - West"

I selected Fixed Sprayhead. Maybe it’s one of the drip nozzles in the list.

post by championc on Apr 16, 2023

Resurrecting an old post, but I wanted to fix an incorrect formula I previously supplied

Nozzle in/hr = (Gallons / mins running / Area in sq. Ft) x 60

Nozzle cm/hr = ((Litres / mins running / Area in m2) X 60)/10

post by earlh on May 24, 2024

This is apparently the correct tool to calculate inches per hour

Water Application Rate Calculator

post by JBTexas on May 28, 2024

Precipitation rate (in/hr) = 96.25 x flow (gpm) / area (sq ft)