Irrigation Schedule Calculator

From crop, climate, and growth stage — how much water and how often. Plus comparison of drip vs overhead vs flood efficiency.

Calculate water needs

Crop

Crop Tomato Pepper Cucumber Squash / zucchini Lettuce Kale / leafy greens Cabbage / brassicas Beans Corn Potato Strawberry Cannabis Industrial hemp Grape Apple Alfalfa Lawn / turf

Growth stage Early / establishment (low water) Mid / vegetative (typical) Peak / fruit/flower (high water) Late / ripening (lower)

Area (sq ft)

Climate

Reference ET (in/day) Cool: 0.10, mod: 0.18, hot/dry: 0.30, desert peak: 0.40

Effective rainfall (in/week) Subtract from gross need

Irrigation method Drip (90% efficient) Micro-sprinkler (80%) Overhead sprinkler (70%) Furrow / flood (50%)

Soil texture Sand (low WHC) Loam (typical) Clay (high WHC)

Reference ET (Evapotranspiration) by climate

Climate	Spring (in/day)	Summer peak	Fall
Cool / coastal (Pacific NW, NE US)	0.08-0.12	0.18-0.25	0.10-0.15
Continental (Midwest, mid-Atlantic)	0.10-0.15	0.22-0.30	0.10-0.15
Hot humid (Southeast, Gulf)	0.12-0.18	0.25-0.32	0.15-0.20
Hot dry (Texas, AZ, CA Central)	0.15-0.22	0.30-0.40	0.18-0.25
Desert / arid (Phoenix, Vegas)	0.20-0.28	0.40-0.55	0.20-0.28

For your specific location, NOAA / NWS, state climate offices, and CIMIS (California) publish daily ETo. Many smart irrigation controllers pull this automatically.

Crop coefficient (Kc) basics

Crop water need = ETo × Kc × area

Where Kc varies by crop AND by stage:

Stage	Typical Kc range
Initial / establishment	0.3 - 0.5
Crop development	0.7 - 0.9
Mid-season / peak	1.0 - 1.2
Late season / ripening	0.5 - 0.9

Irrigation method efficiency

Method	Efficiency	When to use
Drip / drip tape	85-95%	Standard for vegetables, vineyards, orchards. Lowest water use; lowest disease pressure.
Micro-sprinkler	75-85%	Orchards, frost protection, propagation
Overhead sprinkler	65-80%	Field crops, lawns, germination phase. Higher disease and weed pressure.
Furrow / flood	40-60%	Rice, alfalfa, large field. Cheap to install. Massive water use.
Subsurface drip (SDI)	90-95%	Permanent crops, water-scarce regions. Highest installation cost; longest life.

Irrigation timing principles

• Morning over evening. Morning watering = leaves dry by night = fewer fungal diseases.
• Deep, infrequent over shallow, frequent. Deep watering encourages deep roots, drought resistance.
• Match the soil. Sand: smaller volumes more often. Clay: larger volumes less often. Loam: in between.
• Cycle and soak on slopes / clay. 10 min on, 30 min off, repeat — gives water time to absorb without runoff.
• Mulch saves 30-50% water. Even simple straw or wood chip mulch dramatically reduces ET from soil surface.
• Soil moisture sensors beat schedules. A $30 tensiometer pays back in irrigation savings within a season.

Free under CC BY 4.0. Cite as "OAT Irrigation Schedule Calculator (openagriculturetechnology.com)". Crop coefficients from FAO Irrigation and Drainage Paper 56.