Irrigation planning
Garden Water Demand Calculator
Convert garden area and a weekly watering target into estimated gallons, including an allowance for irrigation efficiency.
Convert inches of water to gallons
One inch applied over one square foot is approximately 0.623 gallon. The calculator multiplies area by the weekly application depth, then divides by entered system efficiency to estimate how much water must be delivered.
The one-inch-per-week idea is only a starting point. Rainfall, crop maturity, soil texture, rooting depth, mulch, wind and temperature change actual demand. Check soil moisture rather than running irrigation from the calculator alone.
Use the result for system planning
Weekly gallons help size storage and estimate how long a drip zone must operate. Divide the garden into zones when available supply cannot deliver the entire required flow at once.
Continue with the water tank size calculator and drip flow and runtime calculator.
Frequently asked questions
Does rainfall reduce the result?
Yes. Subtract useful rainfall from the target application before calculating.
What efficiency should drip irrigation use?
Use a conservative value supported by the actual layout and maintenance condition.
Can containers use this method?
Container demand is better estimated per container because exposed media behaves differently from in-ground soil.
Reference: University of Minnesota Extension equates one weekly inch over 100 square feet to about 62 gallons.