Know exactly how much water your crops need.
Avoid overwatering or underwatering and improve yields.
The water requirement of a crop is calculated using this fundamental formula:
Where:
This formula accounts for climate conditions, crop characteristics, and irrigation system losses to provide an accurate estimate of your crop's water needs.
Evapotranspiration (ET₀) combines two processes: evaporation from soil and transpiration from plants. It represents the total water lost to the atmosphere.
The reference ET₀ is based on a standard grass reference crop and varies by climate zone:
| Climate Zone | Typical ET₀ Range (mm/day) | Characteristics |
|---|---|---|
| Arid | 7.0 - 10.0 | Very hot, dry conditions with high water demand |
| Semi-Arid | 5.0 - 7.0 | Hot with seasonal rainfall, still high evaporation |
| Mediterranean | 4.0 - 6.0 | Warm, dry summers and mild, wet winters |
| Humid Tropical | 3.5 - 5.0 | Hot, humid conditions year-round |
| Humid Subtropical | 3.0 - 5.0 | Hot summers, mild winters, regular rainfall |
| Temperate | 2.5 - 4.0 | Moderate temperatures with seasonal changes |
| Continental | 2.0 - 4.0 | Cold winters, warm summers, moderate rainfall |
Reference: FAO Irrigation and Drainage Paper No. 56
The crop coefficient (Kc) varies by crop type and growth stage. Here are average mid-season Kc values for common crops:
| Crop Category | Crop Type | Average Kc Value |
|---|---|---|
| Grains & Cereals | Rice (paddy) | 1.20 |
| Wheat | 1.15 | |
| Maize/Corn | 1.20 | |
| Barley | 1.15 | |
| Vegetables | Tomato | 1.15 |
| Potato | 1.15 | |
| Cabbage | 1.05 | |
| Onion | 1.00 | |
| Fruits | Citrus | 0.65 |
| Banana | 1.10 | |
| Grapes | 0.70 | |
| Legumes & Pulses | Soybean | 1.15 |
| Bean (green) | 1.05 | |
| Groundnut/Peanut | 1.15 | |
| Cash Crops | Cotton | 1.15 |
| Sugarcane | 1.25 | |
| Coffee | 0.95 |
Note: Kc values vary throughout the growing season. Initial, mid-season, and late-season values differ. The calculator uses mid-season values by default.
Source: FAO Irrigation and Drainage Paper No. 56
Apply water directly to the plant root zone with 90% efficiency. Reduces evaporation and runoff significantly.
Add organic materials around plants to retain soil moisture, reduce evaporation, and suppress weeds.
Water early morning or late evening to reduce evaporative losses that occur during hot midday hours.
Use sensors to monitor soil moisture and water only when necessary, preventing over-irrigation.
Collect and store rainwater for irrigation during dry periods, reducing dependence on other water sources.
Strategic under-irrigation during less sensitive growth stages to improve water use efficiency.
Crop water requirement is the total amount of water needed by a crop for normal growth and yield production. It represents the water needed to meet the crop's evapotranspiration demand, which is the combination of water evaporated from the soil surface and water transpired by the plant. It's typically measured in millimeters (mm) of water depth or volume units like liters or cubic meters when considering a specific area.
The standard formula for calculating irrigation water requirement is:
Water Requirement = ET₀ × Kc × Area ÷ Irrigation Efficiency
Where ET₀ is the reference evapotranspiration (mm/day), Kc is the crop coefficient specific to the crop and its growth stage, Area is the field size, and Irrigation Efficiency accounts for water losses in the irrigation system. This formula gives you the gross irrigation requirement, accounting for both the crop's needs and the irrigation system's inefficiencies.
Rice typically requires 900-2,500mm of water per growing season, depending on the cultivation method and climate. For traditional flooded rice (paddy), this translates to approximately 9-25 million liters (2.4-6.6 million gallons) of water per acre throughout the growing season.
However, water-saving methods like Alternate Wetting and Drying (AWD) or System of Rice Intensification (SRI) can reduce water requirements by 15-30%. The specific requirement depends on climate, soil type, rice variety, and cultivation method. Our calculator accounts for these variables to provide an accurate estimate for your specific conditions.
Yes, climate significantly affects crop water needs. The main climate factors that influence water requirements include:
This is why ET₀ (reference evapotranspiration) values vary significantly between different climate zones, from as low as 2-3 mm/day in temperate regions to over 8-10 mm/day in arid regions.
Yes, this calculator is designed to work for a wide range of crops across different regions of the world. It includes data for:
Each crop has specific crop coefficient (Kc) values based on FAO and USDA research. For very specialized or unusual crops not in our database, you can manually input Kc values if you have them from local agricultural extension services or research.