Irrigation measurement calculators

Interactive calculators for pump discharge, applied depth, catch-can uniformity and root-zone soil-water deficit. Each calculator shows the formula behind the result so field measurements become irrigation-ready numbers.

Measure water. Manage every drop.

01

Timed-volume discharge

Collect water in a container of known volume and time each fill. Enter one fill time per trial; the calculator averages the trial discharges.

Collected volumegal Fill times (one per trial)secSeparate trial times with commas. Repeat at least three trials for a reliable average.

FormulaQ = volume ÷ time, averaged across trials

02

Applied irrigation depth

Convert system flow and runtime to an average depth over the irrigated area.

System flowgpm Irrigated areaac Runtimehr Application efficiency%Use a measured value when available.

Methoddepth = applied volume ÷ irrigated area

03

Catch-can uniformity

Paste catch depths to calculate low-quarter distribution uniformity and Christiansen CU.

Catch-can observationsSeparate values with commas, spaces, or line breaks. Keep all observations in the same unit.

FormulaDU_lq = low-quarter mean ÷ overall mean

04

Root-zone soil-water deficit

Estimate the refill needed to return the active root zone to field capacity.

Texture presetTypical values by USDA texture class (after FAO-56, Table 19). Use site-specific soil data when available. Field capacity% VWC Wilting point% VWC Current water content% VWC Active root depthin Application efficiency%

Formuladeficit = (θ_fc − θ_v) × root depth

Measure with a method, not a guess

Good calculations begin with representative observations. Use these short protocols to prepare, measure, and document each field test.

Three habits improve every result

01

Repeat

Collect replicates across representative operating conditions, not just the easiest point to access.

02

Record

Note pressure, wind, runtime, set area, sensor depth, and unusual field conditions with the measurement.

03

Compare

Compare measured performance with design values, prior tests, and crop or soil-water requirements.

Conversions worth keeping close

Use these identities to check units before the result reaches an irrigation schedule.

1 acre-inch27,154US gallons

1 cubic foot/sec448.8US gpm

1 US gpm0.0631liters/sec

1 inch25.4millimeters

References and further reading

Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. (1998). Crop evapotranspiration: Guidelines for computing crop water requirements. FAO Irrigation and Drainage Paper 56.
FAO publication ↗
Burt, C. M., Clemmens, A. J., Strelkoff, T. S., Solomon, K. H., Bliesner, R. D., Hardy, L. A., Howell, T. A., & Eisenhauer, D. E. (1997). Irrigation performance measures: Efficiency and uniformity. Journal of Irrigation and Drainage Engineering, 123(6), 423-442.
Journal article ↗
Christiansen, J. E. (1942). Irrigation by sprinkling. California Agricultural Experiment Station Bulletin 670, University of California, Berkeley.
Digital copy ↗
Merriam, J. L., & Keller, J. (1978). Farm irrigation system evaluation: A guide for management. Utah State University.
USU record ↗
Oregon State University Extension Service. Efficient irrigation of perennial forages with wheel lines in the Pacific Northwest (EM 9399). Authors: I. McGregor, M. I. Zamora Re, G. B. Jones, and T. Peters.
OSU Extension ↗
USDA Natural Resources Conservation Service. (1997). National Engineering Handbook, Part 623, Chapter 9: Water Measurement.
NRCS handbook ↗
USDA Natural Resources Conservation Service. (1997). National Engineering Handbook, Part 652: Irrigation Guide.
NRCS guide ↗
U.S. Department of the Interior, Bureau of Reclamation. (2001). Water Measurement Manual (3rd ed., revised reprint).
USBR manual ↗

Download the field guide (PDF) ↓

Use results with context.

These calculators support field measurements and learning. Verify measurements, assumptions, system limits, and crop requirements before making operational decisions. For questions, contact the AHGRI Lab at floyid.nicolas@oregonstate.edu.