AgricultureID

Calculator · water

Irrigation flow and time calculator

Relate a volume of water, a steady delivery rate and a run time — solve for whichever one is unknown.

Result

Enter volume and available time.

Formula & assumptions

Irrigation time from volume and flow rate

formula v1.0.0 · calc v1 · reviewed 2026-08-27

hours = volume_m³ ÷ (flow_L_per_s × 3.6)

Applies to: Set duration for a known volume at a known steady delivery rate.

Assumptions

  • Flow is steady for the whole period and the whole volume passes through the measured point.

Limitations

  • This is the time to deliver a volume, not the time to wet a soil profile. Infiltration rate, not flow rate, decides whether water enters the soil or runs off.

Sources: National Institute of Standards and Technology (NIST), U.S. Department of Commerce (opens in a new tab), FAO Land and Water Division (opens in a new tab)

Irrigation volume from flow rate and time

formula v1.0.0 · calc v1 · reviewed 2026-08-27

volume_m³ = flow_L_per_s × 3.6 × hours

Applies to: Volume delivered by a set run at a known rate.

Assumptions

  • Flow is steady for the whole period.

Limitations

  • Volume delivered is not volume stored in the root zone. Evaporation, drift, runoff and drainage all sit between the two.

Sources: National Institute of Standards and Technology (NIST), U.S. Department of Commerce (opens in a new tab), FAO Land and Water Division (opens in a new tab)

Flow rate needed for a volume in a set time

formula v1.0.0 · calc v1 · reviewed 2026-08-27

flow_L_per_s = volume_m³ ÷ (hours × 3.6)

Applies to: Sizing a delivery rate against a fixed irrigation window.

Assumptions

  • The volume is delivered evenly across the available time.

Limitations

  • A required flow rate is not a pump specification. Pipe diameter, head and the system’s design flow decide what is achievable.

Sources: National Institute of Standards and Technology (NIST), U.S. Department of Commerce (opens in a new tab), FAO Land and Water Division (opens in a new tab)

Flow rate, litres per second to cubic metres per hour

formula v1.0.0 · calc v1 · reviewed 2026-08-27

m³/h = L/s × 3.6 [3600 s per hour ÷ 1000 L per m³, exact by definition]

Applies to: Any steady volumetric flow.

Assumptions

  • Flow is steady over the period considered.

Limitations

  • A pump’s rated flow is not its delivered flow; head, wear and filtration all reduce it.

Sources: National Institute of Standards and Technology (NIST), U.S. Department of Commerce (opens in a new tab)

About this tool

  • This is delivery arithmetic, not scheduling. It says how long a volume takes to pass a point, not whether the crop needs it, nor whether the soil can absorb it at that rate.
  • Volume delivered is not volume stored in the root zone: evaporation, drift, runoff and deep drainage all sit between the two.

Educational reference — not a prescription

This tool does not determine irrigation requirement. Deciding how much water a crop needs requires evapotranspiration, soil water holding capacity and rainfall, none of which this tool takes as input.

  • These calculators are for education and reference. The quality of any result depends entirely on the accuracy of the values you enter.
  • Local agronomic conditions, legal requirements, product labels, and professional advice may override a general calculation.
  • Results are not pesticide, fertilizer, irrigation, or veterinary prescriptions, and are not a substitute for advice from a qualified agronomist or your local extension service.