Acre-Feet to Gallons Calculator and Conversion Formula

An acre-foot equals 325,851.429 U.S. gallons, so multiply acre-feet by 325,851.429 to convert the volume to gallons. Enter an acre-foot amount in the calculator below to get U.S. gallons, with a cubic-foot equivalent for context.

Formula

Gallons = acre-feet × 325,851.429

• Acre-feet (af) is the volume entered, measured in acre-feet.
• Gallons is the resulting volume in U.S. liquid gallons.

The conversion follows from the definitions: one acre is 43,560 square feet, and one acre-foot is the volume covering one acre to a depth of one foot. A cubic foot contains 7.48051948 U.S. gallons, so 43,560 × 7.48051948 gives approximately 325,851.429 gallons per acre-foot. The calculator’s cubic-foot output uses the direct relationship of 43,560 cubic feet per acre-foot.

Worked Example

Using the default input of 1 acre-foot:

1. Convert to gallons: 1 × 325,851.429 = 325,851.429 U.S. gallons, which rounds to 325,851 gallons.
2. Convert to cubic feet: 1 × 43,560 = 43,560 cubic feet.

The gallon result is rounded to the nearest whole gallon, as shown by the calculator. For a more precise figure, use the formula and retain decimal places in your own calculation.

What an Acre-Foot Measures

An acre-foot is a unit of volume commonly used when discussing water supply, reservoirs, irrigation, and other large quantities of water. It describes a volume, not a water depth on its own: one acre-foot is enough water to cover a one-acre area to a depth of one foot, assuming an even layer and no losses.

An acre is 43,560 square feet. Because an acre-foot combines that area with a depth of one foot, it equals 43,560 cubic feet. In metric units, one acre-foot is approximately 1,233.48 cubic metres, or about 1.233 million litres. Those are rounded conversions; the exact displayed value can vary slightly depending on the precision used for the gallon definition and conversion factor.

The term can be misleading if read as a measure of area. An acre-foot is not an acre, nor does it mean a body of water is necessarily one foot deep everywhere. It is a total volume that could be spread across a particular area at that depth, or stored in a container of another shape.

When to Use the Conversion

Use the calculator when a water quantity is reported in acre-feet but you need to understand it in gallons. The conversion can help compare large storage or supply figures with familiar household-scale units, or check arithmetic when reading a project or water-use description.

• Reservoir volume: Convert a reported storage amount into gallons for a more familiar scale.
• Irrigation planning: Translate a total volume into gallons before considering application rates and field conditions.
• Water accounting: Put quantities from different reports into a common unit, while checking that they refer to the same kind of volume and time period.

A volume conversion does not tell you how quickly water is delivered, how much is available for use, or how much reaches a particular field or household. For a flow rate, such as gallons per minute, you also need a time period or flow measurement. For an actual usable supply, losses, storage limits, and other conditions may matter outside this simple calculation.

Understanding the Result and Its Limits

The first calculator result is U.S. liquid gallons, rounded to a whole gallon. The second is cubic feet, also rounded to a whole cubic foot. Rounding is convenient for large volumes, but it can hide small differences; keep more digits when comparing calculations that require precision.

“Gallon” can mean different things. This calculator uses the U.S. liquid gallon, equal to 231 cubic inches. The imperial gallon used in the United Kingdom and some other contexts is larger, so a conversion to imperial gallons will produce a different result. Check which gallon a source intends before comparing values. The calculator also does not convert to dry gallons, which are used in some specialized contexts.

The formula assumes the input is already expressed in acre-feet. It does not account for evaporation, seepage, sediment, measurement uncertainty, or changes in stored water. If a source gives acre-feet per year, that is a volume rate over time, not a single volume; multiplying by the number of years gives a total only if the stated rate applies throughout that period.

Common Conversion Mistakes

• Confusing area and volume: An acre measures area; an acre-foot measures volume. Do not multiply a number of acres by the gallon conversion unless the depth is one foot or has been accounted for.
• Using the wrong gallon: Confirm whether a figure refers to U.S. or imperial gallons.
• Dropping a decimal or zero: One acre-foot is more than 325,000 U.S. gallons, not 32,585 or 3,258,514 gallons.
• Mixing volume and flow: Gallons and acre-feet measure volume. Gallons per minute and acre-feet per year include a time component.
• Rounding too early: Keep the full conversion factor through intermediate steps, then round the final answer to the precision the task needs.

Frequently Asked Questions

How many gallons are in one acre-foot?
One acre-foot is approximately 325,851.429 U.S. liquid gallons, commonly rounded to 325,851 gallons.

How do I convert acre-feet to gallons?
Multiply the acre-foot value by 325,851.429. For example, 2 acre-feet is about 651,703 U.S. gallons.

How many gallons are in half an acre-foot?
Half an acre-foot is approximately 162,926 U.S. gallons: 0.5 × 325,851.429.

Is an acre-foot the same as an acre?
No. An acre is an area, while an acre-foot is a volume: the volume that would cover one acre to a depth of one foot.

Does this calculator use U.S. or imperial gallons?
It uses U.S. liquid gallons. Imperial gallons are larger, so use an imperial-gallon conversion if that is the unit required.

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in af | Acre-feet | acre-ft | 1 | 0 | 1000000
out gal | U.S. gallons | gal | af * 325851.429 | 0
out ft3 | Cubic feet | ft³ | af * 43560 | 0