Irrigation Calculator
Calculate water requirements, design irrigation systems, and create efficient watering schedules. Save water and maintain healthy plants with science-based irrigation planning.
Irrigation Planning Calculator
Weather & ET Data
Local weather station data
Last 7 days
Distribution uniformity
Irrigation Zones
Zone 1
Cost Analysis (Optional)
Understanding ET & Crop Coefficients
What is ET?
Evapotranspiration (ET) is water lost through plant transpiration and soil evaporation. Reference ET (ETo) is measured from a grass reference surface.
- Low ET (0.1-0.2”): Cool, humid, cloudy days
- Medium ET (0.2-0.3”): Typical spring/fall days
- High ET (0.3-0.4”): Hot, dry, windy summer days
- Very High ET (>0.4”): Extreme heat conditions
Crop Coefficients (Kc)
Kc values adjust ET for specific plants. Plant ET = ETo × Kc
- Low Kc (0.3-0.5): Native plants, drought-tolerant
- Medium Kc (0.6-0.8): Established trees, shrubs
- High Kc (0.8-1.0): Lawns, groundcovers
- Very High Kc (>1.0): Vegetables, annual flowers
Irrigation Calculator Guide
Efficient irrigation saves water, reduces costs, and promotes healthier plants. This calculator uses scientific principles including evapotranspiration (ET) and soil water balance to create optimal watering schedules.
Key Irrigation Principles
1. Water Deep but Infrequently
- Encourages deep root growth
- Improves drought tolerance
- Reduces disease problems
- Saves water compared to daily light watering
2. Consider Soil Type
- Sandy soil: Low water holding, frequent irrigation needed
- Loam soil: Ideal balance, moderate frequency
- Clay soil: High water holding, less frequent but longer runtime
3. Adjust for Conditions
- Sun exposure: Full sun areas need more water
- Slope: Steep slopes need shorter, more frequent cycles
- Wind: Increases ET and reduces sprinkler efficiency
- Season: Adjust schedules monthly as ET changes
Irrigation System Efficiency
- Drip irrigation: 85-95% efficiency
- Rotary nozzles: 80-85% efficiency
- Rotor heads: 75-80% efficiency
- Spray heads: 70-75% efficiency
- Hand watering: 50-70% efficiency
Best Practices
- Water early morning (4-8 AM) to minimize evaporation
- Avoid watering during windy conditions
- Check and maintain system regularly
- Use rain sensors to prevent overwatering
- Group plants with similar water needs
- Mulch to reduce evaporation
Cycle and Soak Method
For clay soils or slopes, use multiple short cycles instead of one long runtime. This allows water to infiltrate without runoff. For example, instead of 30 minutes once, run 3 cycles of 10 minutes with 30-60 minute breaks between.
Seasonal Adjustments
- Spring: Gradually increase watering as temperatures rise
- Summer: Peak water needs, may need daily watering
- Fall: Reduce frequency as temperatures drop
- Winter: Minimal or no irrigation in many climates
Garden questions, answered
Common questions before you buy materials
Use these quick answers alongside the calculator so you can plan the right amount, avoid waste, and keep your garden project moving.
- How long should I run drip irrigation?
- Run time depends on emitter flow, plant needs, soil type, and weather. The goal is to wet the root zone deeply without leaving soil soggy.
- Is drip irrigation better than sprinklers for garden beds?
- Drip irrigation is often better for beds because it waters soil near roots and keeps leaves drier. Sprinklers can be useful for lawns or newly seeded areas.
- When should I water the garden?
- Morning watering is usually best. It reduces evaporation compared with midday watering and gives leaves time to dry before evening.