Irrigation Run Time Calculator

Calculate how long to run your irrigation system to apply a target water depth. Accounts for flow rate and application efficiency.

Results

Run Time (hours)-

Run Time (minutes)-

Water Applied (gallons)-

Water per Acre (gallons)-

Formula & How It Works

Run Time (hr) = (Depth in × Area acres × 27,154) ÷ (GPM × 60 × Efficiency%)

27,154 = gallons in one acre-inch (43,560 sq ft × 1/12 ft × 7.48 gal/cu ft).

Calculation Example

1 inch to 10 acres at 500 GPM, 80% efficiency: Time = (1×10×27,154)÷(500×60×0.80) = 11.31 hr = 679 min. Water = 339,425 gal.

How to Use This Calculator

1. Target depth from ET or soil moisture. 2. Area. 3. Measured flow rate. 4. Efficiency (70-90% sprinkler, 85-95% drip). Calculate.

About This Tool

Proper scheduling ensures adequate water without waste. Over-irrigation wastes water and leaches nutrients. Under-irrigation stresses crops and reduces yield.

Applicability: Suitable for irrigation planning in North America and Europe, adaptable to semi-arid and Mediterranean climates worldwide.

References & Sources:

Source: USDA NRCS, Irrigation Water Management Guide, National Engineering Handbook, Part 652, 2024.
Reference: FAO Irrigation and Drainage Paper 56, Crop Evapotranspiration: Guidelines for Computing Crop Water Requirements, 2023.
Reference: ASABE Standard S437.1, Irrigation Scheduling and Water Application Efficiency.

Reviewed by Agricalc Editorial Team — Agricultural engineers and agronomists with 10+ years of field experience. Our team verifies every calculator formula against peer-reviewed extension publications. For site-specific advice, consult your local agronomist.

Common Mistakes & Tips

Using rated GPM not measured (often 10-20% lower). Ignoring efficiency. Applying faster than infiltration rate causes runoff.

References & Sources

FAO (Food and Agriculture Organization) — Agricultural production and nutrition guidelines
USDA NRCS — Field Office Technical Guide and conservation practice standards
Land-Grant University Cooperative Extension System — crop and livestock recommendations
FAO — Water for Agriculture
USBR — Water Management

Frequently Asked Questions

What is 27,154? ▼

Gallons in one acre-inch: 43,560 sq ft × 1/12 ft × 7.48 gal/cu ft.

What efficiency to use? ▼

Drip 85-95%, center pivot 75-85%, sprinkler 65-75%, flood 50-70%.

How often to irrigate? ▼

When soil moisture drops to 50% available water. Use sensors or ET scheduling.

What units does the Irrigation Run Time Calculator use? ▼

Target depth in inches, area in acres, flow in GPM, efficiency in %. Results in hours, minutes, gallons applied, and gallons per acre.

How do I use the Irrigation Run Time Calculator correctly? ▼

Start by gathering accurate input values from your farm records or measurements. Enter each value in the specified units, then click Calculate. Review all results carefully — cross-check the primary output against your own experience or extension recommendations. For best results, use actual measured values rather than estimates, and recalibrate whenever conditions change.