The Field Calculators → Water
Water
Irrigation requirement & run time
How much water the garden actually wants this week, and how long to run the zone to deliver it.
Result
Area irrigated800 sq ft
Water needed1 in/week
Rain already received0 in
System efficiency90 %
Zone flow rate60 gal/hr
Water to apply this week
554 gallons
1.00 in deficit over 800 sq ft.
Run time
9.2 hours
Split it: two or three deep soakings beat seven shallow ones.
Per watering, if 2× per week
4.6 hrs
Season total (20 weeks, no rain)
11,076 gal
What this will not do
- Water by the soil probe, not by this number. A moisture sensor at root depth answers the only real question — is it dry down there — and it accounts for your soil, which an inch-per-week rule cannot.
- Deep and infrequent beats shallow and daily. Shallow watering trains roots to live in the top inch, which is exactly where the soil dries out first.
- Drip needs a pressure regulator and a filter or it dies: emitters are designed for ~10–25 psi and your hose bib is 40–60.
The full build and the reasoning are in Chapter 18 of the guide.