Irrigation Requirement (ET-based, acre-feet)
Crop ET demand (Kc x ET0 x days), net and gross irrigation depth after rainfall and application efficiency, and total acre-feet / gallons over the field. Per FAO Irrigation and Drainage Paper 56 and the USDA NRCS Irrigation Guide; reference ET0 from your local station.
Formula and source
ET_crop = Kc x ET0 x days. Net depth = max(0, ET_crop - effective rainfall). Gross depth = net / application efficiency. Total = gross_in x acres / 12 (acre-feet); gallons = acre-ft x 325,851.
FAO Irrigation and Drainage Paper 56 (Crop Evapotranspiration, Allen et al. 1998) by name; USDA NRCS Irrigation Guide by name. Kc values from FAO 56 Table 12.
Audience
This tile is built for agriculture and the adjacent professions in the Agriculture and Forestry group. The interactive calculator runs entirely in your browser. No account, no fee, no advertising, no tracking.
Related tools
Posture
Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.