Acre Foot to Gallons Calculator

This calculator converts an acre foot—the volume of water needed to cover one acre to a depth of one foot—into US gallons. Enter the number of acre feet, and you get the equivalent volume in gallons instantly, along with the same volume expressed in cubic feet and liters for easy reference.

Formula

The conversion relies on a single, fixed relationship: one acre foot equals exactly 43,560 cubic feet (because one acre is 43,560 square feet, and the depth is one foot). To convert that to gallons, you multiply by 7.48051948, the number of US gallons in one cubic foot. The full formula is:

Gallons = Acre feet × 43,560 × 7.48051948

Combining the two constants gives Gallons = Acre feet × 325,851.4286. The calculator uses the more precise factor of 325,851.428571 gallons per acre foot, which is the standard value used in water resource management. The cubic feet output simply multiplies acre feet by 43,560, and the liter output multiplies acre feet by 1,233,481.84 (since one US gallon equals 3.785411784 liters).

Worked Example

Using the default value of 1 acre foot:

1. Start with the volume in acre feet: 1
2. Convert to cubic feet: 1 × 43,560 = 43,560 ft³
3. Convert cubic feet to gallons: 43,560 × 7.48051948 = 325,851.43 gallons
4. Convert gallons to liters: 325,851.43 × 3.785411784 = 1,233,481.84 liters

The calculator shows 325,851.4 gallons, 43,560 cubic feet, and 1,233,481.8 liters for 1 acre foot, matching these steps.

What Is an Acre Foot?

An acre foot is a unit of volume commonly used in the United States for large-scale water resources—irrigation, reservoir capacity, municipal water supply, and agricultural usage. It represents the amount of water required to cover one acre of land (about 43,560 square feet, roughly the size of a football field) to a depth of one foot. To visualize it, imagine a football field covered in water up to your ankles—that is about one acre foot. In metric terms, an acre foot is approximately 1,233 cubic meters or 1.23 million liters.

This unit is preferred over gallons for large water projects because the numbers stay manageable. A typical household might use 0.5 to 1 acre foot per year, while a large farm can use tens or even hundreds of acre feet annually. Reservoirs are often measured in thousands of acre feet.

Why Convert to Gallons?

While acre feet are convenient for planning, most billing, delivery, and regulatory contexts use gallons or cubic meters. If you are buying water from a district, filing a water right, or comparing your usage to a municipal average, you will likely need gallons. For example, a small lake of 100 acre feet holds about 32.6 million gallons—a number that makes sense when comparing to a city’s daily consumption or a treatment plant’s capacity. The conversion also helps when you are trying to estimate how long a water supply will last based on a daily usage rate in gallons.

Common Mistakes and Misconceptions

• Using the wrong gallon: The US gallon (231 cubic inches) is different from the Imperial gallon (277.42 cubic inches). This calculator uses US gallons, which is the standard for most water measurements in the US. If you need Imperial gallons, multiply the US gallons by 0.832674.
• Confusing acre foot with acre inch: An acre inch is one-twelfth of an acre foot. Many irrigation schedules use acre inches, so be sure you are converting the right unit. One acre inch equals about 27,154 gallons.
• Rounding too early: The conversion factor 325,851.4286 is already rounded. If you use 325,000 or 326,000, you will be off by hundreds of gallons for even a single acre foot. For large volumes, the error compounds.
• Forgetting that acre feet are volume, not flow: An acre foot is a static volume. Flow rates (like gallons per minute) require a time component. A canal delivering 1 acre foot per day is very different from one delivering it per hour.

How to Read the Results

The headline result is the volume in US gallons, rounded to one decimal place. This is the number you will use for billing, reporting, or comparison. The cubic feet output is useful if you are working with pump curves or pipe flow calculations, where cubic feet per second is common. The liters output helps if you are comparing to international standards or metric-based reports. For most practical purposes, the gallons figure is what you need. If you are planning a water delivery, you might also want to convert gallons to tanker truck loads (typically 8,000–10,000 gallons each) or to inches of irrigation depth over a specific area—but that requires additional inputs.

Limitations of the Conversion

This conversion is purely volumetric—it does not account for evaporation, seepage, or water quality. If you are estimating how much water you need to fill a pond or irrigate a field, you must add a loss factor. For example, a pond might lose 10–20% of its volume to evaporation and seepage over a season, so you would need to order more than the calculated acre feet. Similarly, irrigation efficiency (how much water actually reaches the plant roots) is typically 50–80%, so the gross water requirement is higher than the net. This calculator gives you the exact mathematical conversion, but real-world applications always require adjustments for these factors.

Frequently Asked Questions

How many gallons are in half an acre foot?

Half an acre foot equals 162,925.7 US gallons. You can get this by multiplying 0.5 by 325,851.4286, or simply enter 0.5 into the calculator. This is a common amount for a small pond or a single irrigation event on a few acres.

What is the difference between an acre foot and a cubic foot?

A cubic foot is a cube measuring 1 foot on each side. An acre foot is 43,560 cubic feet—the area of an acre times one foot of depth. The acre foot is a much larger unit, used for water volumes where cubic feet would be unwieldy. For example, a swimming pool might be 1,000 cubic feet, while a farm pond is often several acre feet.

How many gallons are in an acre inch?

One acre inch is exactly 27,154.29 US gallons. This is simply the acre foot conversion divided by 12. Many irrigation systems are measured in acre inches, especially for short-term water applications, so this is a handy number to remember.

Is an acre foot the same as a megaliter?

No, but they are close. One acre foot equals approximately 1.233 megaliters (million liters). The exact value is 1,233,481.84 liters. If you are comparing Australian or European water reports that use megaliters, you can convert by multiplying acre feet by 1.233.

Why do water districts use acre feet instead of gallons?

Because the numbers are more manageable. A city’s annual water use might be 100,000 acre feet—that is 32.6 billion gallons. Acre feet avoid extremely large numbers and relate directly to land area, which is how agricultural water is allocated. It is a practical unit for planning and rights, even though gallons are more familiar to the public.

How do I convert acre feet to gallons for a reservoir?

Simply multiply the reservoir’s capacity in acre feet by 325,851.4286. For example, a reservoir with 500 acre feet holds about 162.9 million gallons. This helps you understand the reservoir’s yield in terms of daily municipal demand (e.g., a city using 50 million gallons per day would draw it down in about 3.3 days if no inflow).

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in af | Acre feet | - | 1 | 0 | 1000000
out gal | Gallons | US gal | af * 325851.428571 | 1
out ft3 | Cubic feet | ft³ | af * 43560 | 0
out l | Liters | L | af * 1233481.84 | 1