Irrigation Duty Cycle Calculator

Irrigation Duty Cycle Explained

Irrigation planning starts with the water depth your crops need each week. A common guideline is about 1 inch (25 mm) per week, but demand varies with crop type, soil texture, and weather. Once you know the required depth, you can convert it into a water volume based on area. In imperial units, 1 acre-inch equals approximately 27,154 gallons. In metric units, 1 mm of water over 1 square meter equals 1 liter, making conversions straightforward for garden beds and greenhouse benches.

Duty cycle is the runtime required to deliver that volume through your system’s flow rate. For example, if your system flows 6 GPM and you need 1,200 gallons per week, the total runtime is 200 minutes. Splitting that runtime across multiple sessions improves infiltration and reduces runoff, especially on clay soils or slopes. The per-session runtime output helps you schedule timers and drip zones for efficient watering.

This calculator is designed for precision farming and homesteading alike. It is most accurate when you use measured flow rates and real garden areas. Combine the results with soil moisture monitoring and rainfall data for a smart irrigation strategy. Efficient watering conserves water, improves nutrient uptake, and supports healthy crops from small raised beds to larger farm plots.

If your system has an application rate (in/hr or mm/hr), you can use it to validate runtime against the recommended weekly depth. For example, a system applying 0.5 in/hr needs roughly two hours to deliver 1 inch of water. Drip systems often deliver slowly but efficiently, which is ideal for deep rooting and reduced evaporation. Use the per-session runtime to avoid surface runoff and to keep soil moisture in the root zone, especially in sandy soils where water percolates quickly.

Weather-based adjustments are essential. If you receive rainfall, subtract it from the weekly target depth before calculating runtime. Many growers use rain gauges or soil sensors to track real-world inputs. This keeps irrigation aligned with crop demand and helps prevent waterlogging or nutrient leaching after storms.

Formula

For imperial units, gallons needed = area (acres) × depth (in) × 27,154. For metric, liters needed = area (m²) × depth (mm). Runtime = volume ÷ flow rate.

Example Calculation

A 1,000 ft² garden needs 1 inch of water. That equals 1,000 × 0.623 = 623 gallons. With a 6 GPM system, runtime is about 104 minutes per week. Split into two sessions, each runs 52 minutes.

FAQs

How much water do gardens need?

About 1 inch (25 mm) per week is common, but adjust for crop and climate.

What is duty cycle?

The total runtime required to deliver the weekly volume through your system.

Can I use metric units?

Yes. Use square meters, millimeters, and liters per minute.

Should I split watering sessions?

Yes. Multiple sessions improve infiltration and reduce runoff.

Are results private?

Yes, everything runs locally in your browser.

How it works

This calculator converts water depth to volume and divides by flow rate for runtime. All computation runs client-side for privacy and speed.

Disclaimer

Weekly water needs vary by climate and crop. Use soil moisture data and local guidance to refine schedules.