What Is Acre-Foot?
An acre foot is a way to measure a big amount of water. It tells you how much water it would take to cover one acre of land with water that is one foot deep.
This unit is often used for rivers, lakes, dams, and farm irrigation, where the amounts of water are too large to count in buckets or small containers.
In simple words, acre foot is a special measuring box for water that is long enough and wide enough to cover a field the size of an acre and filled up to one foot high.
Definition
An acre foot is a unit of volume. It is built from two other units.
- Acre measures area, like the size of a piece of land.
- Foot measures length or depth.
One acre foot is the volume of water that covers:
- Area: 1 acre of land
- Depth: 1 foot of water
In exact numbers:
- 1 acre foot = 43,560 cubic feet
- 1 acre foot ≈ 325,851 US gallons
- 1 acre foot ≈ 1,233 cubic meters
- 1 acre foot ≈ 1,233,000 liters
So one acre foot is a little over one million liters of water. That is enough water to fill many backyard swimming pools.
History / Origin
The acre foot grew out of land and farming needs.
- The word acre comes from old English farming. It was the amount of land a farmer could plow in one day with oxen.
- The foot has long been used as a basic length unit in English speaking countries.
When farmers and engineers started building canals, wells, and dams, they needed a simple way to talk about large water amounts for land. They joined the land unit acre with the depth unit foot and created acre foot.
The acre foot became common in the western United States in the late 1800s and early 1900s, when people were planning big irrigation projects and sharing river water between farms, cities, and states.
Symbol & Abbreviation
There is no single worldwide symbol, but several short forms are used in practice.
- acre ft
- ac ft
- acre foot written in full
- AF sometimes used in charts and graphs
All of these mean the same thing. You can read them as acre foot. In formal science work, people often also write the size in cubic meters in brackets, for example 1 acre ft (≈ 1,233 m³).
Current Use Around the World
Acre foot is most common in places that use acres and feet for land and building measurements.
Most common uses:
- United States water rights, river sharing, and water laws
- Western US farming measuring water for irrigation and crop needs
- Reservoirs and dams storage capacity and yearly inflow or outflow
- Groundwater size of aquifers and pumping amounts
- City water planning counting how much water a city uses in a year
Some parts of Canada and a few other countries that use acres in land records may also use acre feet, but most of the world now prefers cubic meters for water planning.
Even in countries that use the metric system, older water reports and legal documents may still show values in acre feet, especially for shared rivers or cross border projects.
Example Conversions
Here are some helpful conversion examples to see how big an acre foot is.
| Acre feet | Cubic feet | US gallons | Cubic meters | Liters |
|---|---|---|---|---|
| 1 acre foot | 43,560 ft³ | ≈ 325,851 gal | ≈ 1,233 m³ | ≈ 1,233,000 L |
| 0.5 acre foot | 21,780 ft³ | ≈ 162,925 gal | ≈ 616.5 m³ | ≈ 616,500 L |
| 2 acre feet | 87,120 ft³ | ≈ 651,702 gal | ≈ 2,466 m³ | ≈ 2,466,000 L |
| 10 acre feet | 435,600 ft³ | ≈ 3,258,510 gal | ≈ 12,330 m³ | ≈ 12,330,000 L |
To give a feeling for size, 1 acre foot of water is often enough to supply several homes with water for a full year, depending on how much water each home uses.
Related Units
Acre foot is related to many other volume and area units.
- Cubic foot (ft³) the base unit that makes up an acre foot, 1 acre foot = 43,560 ft³.
- Cubic meter (m³) the main metric volume unit for large amounts of water, 1 acre foot ≈ 1,233 m³.
- Liter (L) metric unit often used for drinks and small containers, 1 m³ = 1,000 L, so 1 acre foot ≈ 1,233,000 L.
- US gallon common liquid unit in the United States, 1 acre foot ≈ 325,851 gallons.
- Acre unit of land area used in the United States and some other places, 1 acre ≈ 4,047 square meters.
- Hectare meter metric style unit similar to acre foot, it is the water needed to cover one hectare of land with water 1 meter deep.
FAQs
What is an acre foot in simple words?
An acre foot is how much water it takes to cover a field that is one acre in size with water that is one foot deep.
How many gallons are in one acre foot?
One acre foot is about 325,851 US gallons of water. You can round this to about 326,000 gallons for quick estimates.
How many cubic meters are in one acre foot?
One acre foot is about 1,233 cubic meters. This is a little more than one million two hundred thousand liters.
Why do people use acre feet instead of gallons?
For rivers, lakes, and big farms, the amounts of water are very large. Using gallons would give huge numbers that are hard to read. Acre feet keep the numbers smaller and easier to compare.
Where is the acre foot mostly used?
Acre foot is mostly used in the United States, especially in the western states, for water rights, irrigation, and reservoir planning. Some older Canadian and other records also use it.
Is acre foot a metric unit?
No. Acre foot is based on acres and feet, which are not metric units. The closest metric unit for the same type of work is the cubic meter.
How much water does one acre foot give to homes?
The exact number depends on how much water each home uses, but in many places one acre foot can supply several average homes for a full year.
Can I convert acre feet to liters or gallons by hand?
Yes. Use these facts. 1 acre foot = 43,560 cubic feet, 1 cubic foot ≈ 7.48 US gallons, and 1 cubic meter = 1,000 liters. Or use online calculators for fast results.