RevenueLab.fyi
Revenue Rex logo mark
🧰 Other · Rex's Toolbox

Irrigation Requirement Calculator

Inches of water, gallons, and run time for a field or garden.

Revenue Rex peeking

Rex says

Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.

Try a scenario

Click to load — tweak from there.

Inputs

Result

Water to apply (inches)

1.46

Total gallons

39,713

System run time (hours)

26.48

Net crop need (inches)

1.17

Acre-inches applied

1.46

Revenue Rex peeking

Psst — share this and help Rex grow

One click, a permanent link with your numbers baked in.

More other

How to use this

  1. 1Enter area (acres).
  2. 2Enter reference et this period (in).
  3. 3Enter crop coefficient (kc).
  4. 4Enter effective rainfall (in).
  5. 5Enter system efficiency (%).
  6. 6Enter system flow rate (gpm).
  7. 7Read your water to apply (inches) on the right — it updates as you type.
  8. 8Hit Share to keep the scenario or send it to someone.

About this calculator

Work out the irrigation deficit from evapotranspiration and rainfall, convert it into gallons for your area, and translate that into system run time at your flow rate.

FormulaDeficit = (ET × Kc − rainfall) ÷ efficiency. 1 acre-inch = 27,154 gallons.

Worked example

Using the values the calculator loads with:

Inputs

  • Area: 1 acres
  • Reference ET this period: 1.4 in
  • Crop coefficient (Kc): 1.05
  • Effective rainfall: 0.3 in
  • System efficiency: 80 %
  • System flow rate: 25 gpm

Results

  • Water to apply (inches): 1.46
  • Total gallons: 39,713
  • System run time (hours): 26.48
  • Net crop need (inches): 1.17
  • Acre-inches applied: 1.46

What each field means

Inputs

Area (acres)
The area used in the calculation, measured in acres. Starts at 1 acres so you have a working example on load.
Reference ET this period (in)
The reference et this period used in the calculation, measured in in. Starts at 1.4 in so you have a working example on load.
Crop coefficient (Kc)
The crop coefficient (kc) used in the calculation. Starts at 1.05 so you have a working example on load. Accepted range: 0.1–1.5.
Effective rainfall (in)
The effective rainfall used in the calculation, measured in in. Starts at 0.3 in so you have a working example on load.
System efficiency (%)
The system efficiency used in the calculation, measured in %. Starts at 80 % so you have a working example on load. Accepted range: 20–100 %.
System flow rate (gpm)
The system flow rate used in the calculation, measured in gpm. Starts at 25 gpm so you have a working example on load.

Results

Water to apply (inches)
Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Total gallons
Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
System run time (hours)
Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Net crop need (inches)
Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Acre-inches applied
Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.

FAQ

Where do I get reference ET?

State extension networks and most weather services publish daily ET₀ by region. Sum it across the days since your last irrigation.

What's a crop coefficient?

A multiplier for crop stage. Seedlings sit near 0.3, full canopy near 1.1–1.2, and senescence drops back down.

Accuracy and limitations

  • Estimates assume standard, average conditions — local rules, pricing, and materials vary.
  • Results are rounded for readability; add a buffer before ordering, booking, or committing.
  • Double-check anything with a real cost attached against a local quote.

Cite this calculator

Writing about this topic? Grab a citation — every link helps keep these tools free.

APA
RevenueLab. (2026). Irrigation Water Requirement Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/irrigation-water-need
HTML
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/irrigation-water-need" target="_blank" rel="noopener">Irrigation Water Requirement Calculator — RevenueLab</a> (2026).</p>
Markdown
Source: [Irrigation Water Requirement Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/irrigation-water-need) (2026).
Advertisement