inch of depth
Volume per areaexact by definition
An inch of depth is exactly 0.0254 m³/m², a volume per area rather than a plain length. It is the unit of North American irrigation scheduling and of the acre-inch, and equals exactly 27,154.29 US gallons per acre.
Why it is written : Written "in", the same symbol as the length, for the same reason the millimetre of depth is: a depth of water on the ground is a length. Listed separately here so it can be converted against gallons per acre.
| 1 | 254,000 |
About the inch of depth
North American irrigation runs on the inch and its close relative the acre-inch — the volume of water that covers one acre one inch deep.
1 acre-inch = 27,154 US gallons = 3,630 cubic feet = 102.8 cubic metres.
That first figure is worth memorising, because it turns a pump rate into a schedule. A well delivering 500 gpm produces 27,154 ÷ 500 = 54.3 minutes of pumping per acre-inch, so putting an inch on a 60-acre pivot takes roughly 54 hours of continuous running.
An inch is 25.4 mm, so a crop using 0.25 in/day is using 6.4 mm/day, and the two scheduling traditions describe the same thirsty corn field.
One inch of depth in every volume per area unit
| 254,000 | liter per hectare (L/ha) | |
| 254 | cubic meter per hectare (m³/ha) | |
| 25,400 | milliliter per square meter (mL/m²) | |
| 25.4 | millimeter of depth (mm) | |
| 2.54 | centimeter of depth (cm) | |
| 27,154.3 | US gallon per acre (gal/ac) | |
| 623.377 | US gallon per thousand square feet (gal/1000 ft²) | |
| 1 | inch of depth (in)this unit |