This calculator converts a volume in acre-feet to US gallons. Enter the number of acre-feet, and you get the equivalent volume in gallons instantly. It also shows the result in cubic feet for reference.
Formula
The conversion uses a fixed relationship between acre-feet and gallons:
Gallons = Acre-feet × 325,851.428571
Where:
- Acre-feet (ac-ft) – a unit of volume commonly used in the US for large water bodies, irrigation, and reservoir capacity. One acre-foot is the volume of water that would cover one acre of land to a depth of one foot.
- Gallons (US gal) – the standard US liquid gallon, equal to 231 cubic inches.
The factor 325,851.428571 comes from the exact definition: 1 acre-foot = 43,560 cubic feet (since 1 acre = 43,560 ft²) and 1 cubic foot = 7.48051948 US gallons. Multiplying gives 43,560 × 7.48051948 = 325,851.428571 gallons.
Worked Example
Using the default value of 1 acre-foot:
- Start with 1 acre-foot.
- Convert to cubic feet: 1 × 43,560 = 43,560 ft³.
- Convert cubic feet to gallons: 43,560 × 7.48051948 = 325,851.428571 gallons.
The calculator rounds to the nearest whole gallon, so it displays 325,851 gallons for 1 acre-foot.
Why Use Acre-Feet?
Acre-feet are used in agriculture, hydrology, and municipal water management because they describe large volumes in terms of land area and depth. For example, a farmer might say a field needs 2 acre-feet of water per season. That is about 651,703 gallons – a number that is unwieldy but meaningful when planning irrigation schedules or reservoir releases.
The unit is also used in water rights and legal contracts, especially in the western United States. Understanding the gallon equivalent helps when comparing water usage to household consumption (average US household uses about 300 gallons per day) or when estimating costs if water is billed per gallon.
How to Use the Calculator
Simply type the number of acre-feet into the input field. The calculator accepts any non-negative value, from tiny fractions (like 0.001 acre-feet for a small pond) to very large numbers (like 100,000 acre-feet for a major reservoir).
- For a typical residential swimming pool (about 0.5 acre-feet), you get about 162,926 gallons.
- For a large irrigation canal delivering 50 acre-feet per day, that is about 16,292,571 gallons per day.
The result is rounded to the nearest whole gallon because fractional gallons are rarely useful at this scale. For precision work, you can use the exact factor 325,851.428571 in your own calculations.
Common Mistakes and Misconceptions
A frequent error is confusing US gallons with imperial gallons (used in the UK and Canada). One imperial gallon is about 1.2 US gallons, so the conversion factor differs. This calculator uses US gallons, which is the standard for most water measurements in the US.
Another mistake is mixing up acre-feet with acre-inches. One acre-inch is 1/12 of an acre-foot, so 1 acre-inch equals about 27,154 gallons. If you have a value in acre-inches, divide by 12 to get acre-feet first.
Also, note that the acre-foot is a volume unit, not a flow rate. A flow rate of 1 acre-foot per day is about 226 gallons per minute, but that conversion requires time, which this calculator does not handle.
Practical Applications
Knowing the gallon equivalent of acre-feet is useful in several real-world situations:
- Reservoir capacity: A small lake of 500 acre-feet holds about 163 million gallons – enough for a small town for a year.
- Irrigation planning: If your crop needs 1.5 acre-feet per acre per season, you can calculate the total gallons needed for your field.
- Water bills: Some agricultural water districts charge per acre-foot, but if you are comparing with residential rates per gallon, this conversion helps.
- Environmental reporting: Streamflow or groundwater recharge is often reported in acre-feet per year; converting to gallons can make the scale more intuitive for public communication.
Limitations and Accuracy
The conversion factor is exact based on definitions, but the practical accuracy depends on the precision of your acre-foot measurement. Surveying errors, evaporation, and seepage can all affect actual water volume. For legal or financial decisions, always consult a professional hydrologist or water rights specialist.
The calculator uses the standard US gallon definition. If you need imperial gallons, multiply the result by 0.832674. For cubic meters, multiply the acre-feet by 1,233.48 (since 1 acre-foot = 1,233.48 m³).
Frequently Asked Questions
How many gallons are in one acre-foot?
Exactly 325,851.428571 US gallons. That is 43,560 cubic feet times 7.48051948 gallons per cubic foot. Most calculations round to 325,851 gallons.
What is an acre-foot in simpler terms?
Imagine a football field (including end zones) covered with water one foot deep. That is about one acre-foot. It is a large volume – enough to supply a family of four for about a year.
How do I convert acre-inches to gallons?
First convert acre-inches to acre-feet by dividing by 12 (since there are 12 inches in a foot). Then multiply by 325,851.428571. For example, 3 acre-inches = 0.25 acre-feet = 81,462.857 gallons.
Is an acre-foot the same as a cubic foot?
No. An acre-foot is 43,560 cubic feet. A cubic foot is a much smaller unit – about 7.48 gallons. The acre-foot is used for large-scale water volumes, while cubic feet are used for smaller measurements.
How many gallons are in a cubic foot?
There are exactly 7.48051948 US gallons in one cubic foot. This is the conversion factor used to derive the acre-foot to gallon relationship.
Why do some water bills use acre-feet instead of gallons?
Acre-feet are more convenient for large volumes because the numbers are smaller and relate directly to land area and depth. A typical agricultural water use might be 2 acre-feet per acre, which is easier to visualize than 651,703 gallons.
Related
Formula used
in af | Acre-feet | ac-ft | 1 | 0 | 1000000 out gal | Gallons | US gal | af * 325851.428571 | 0 out ft3 | Cubic feet | ft³ | af * 43560 | 0
Each line is one input (in, sel, list) or one result (out: label, unit, formula, decimals). How the calculators work
Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.
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