# How to calculate inches per hour for subsurface dripline

I have installed a Railbird XFS subsurface dripline for vine around my home. How do I calculate the inches per hour when setting up a custom emitter?

For example, if the flow rate is 0.6 gph for each emitter, and they are spaced 12 inches apart. What would be the inches/hr of a 100’ length of dripline? what is the formula to use?

Hello @marlowkc

Thank you for reaching out to us.

Do you know if the Rainbird XFS subsurface you installed is a grid? I only ask because if there are two emitters per square foot that could make a difference on the precipitation rate.

Let me know.

Thanks,
Kevin

Right! Not in a grid though, just a straight line to water a skinny bed of vines.

Great. Thanks for clarifying.

0.9625 cu. in./hr would be the precipitation rate if the flow rate is .6 GPH. This is based on 1 square foot.

Let me know if you have any additional questions.

Thanks again,
Kevin

Thanks for your help. One follow up question: Do I need to adjust for subsurface vs. surface drip irrigation? The reason I’m wondering is, although surface emitters are more efficient than spray heads, surface emitters aren’t quite as efficient as subsurface emitters—the latter delivers water right at the root system. Assuming you take runoff into account when determining watering times for spray heads, I want to make sure I do not overwater by just supplementing the flow rate of my dripline for the flow rate of a spray head.

Hi @marlowkc,

You’ll want to adjust the efficiency of the zone. I’d ballpark a subsurface drip line to be 80-90% efficient. It’s very hard to achieve 100% efficiency.

Hope this helps!

Steve,

This was very informative. I have a similar question about the drip line. I have a hunter drip line which is 1.0 gph. Mine is set up for the trees where a line runs behind the trees and in front of the trees. Woul really appreciate help in determining the nozzle to use.

Thank you.

@epelba01, it was a pleasure chatting with you this afternoon. Did you get the support email I sent you with the links on how to calculate your precip rates?

Best, Emil

I did. It went to spam in error. Thank you.

@epelba01, anytime, happy to help!

Did you have any other questions we could assist you with in the setup of your Iro? Happy to help with calculating precip rates, reviewing schedules, etc.

Best, Emil

I have the same 1gph drip line. Can I get that calculation as well?

@milnejames, assuming you have a 1 GPH that waters an area of roughy 1 square foot, the precip rate would be 1.60 in/hour.

For details, please reference this support article: http://support.rachio.com/article/316-precipitation-rates

Hope this helps

Best, Emil

Here are some quick reference calculations:

Precip Rates for Drip (ft²)

• 1.6 in/hr = 1.0 gph/ft²
• 1.44 in/hr = 0.9 gph/ft²
• 0.96 in/hr = 0.6 gph/ft²
• 0.64 in/hr = 0.4 gph/ft²

Precipitation Rate (PR drip grid pattern) (always inches/hour)

• (231.1* x Emitter Flow Rate) ÷ (Emitter Spacing x Row Spacing)
• e.g. (231.1 x 1 GPH) ÷ (12 x 12) = 2.3”/hr

Hope that helps!
Tigre

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