Gallons to Acre Feet Converter

Related Calculators

Table of contents

• How to use
• Common mistakes
• Definitions
• Methodology
• Limitations & assumptions
• Sources

US liquid gallon: The gallon type used by this converter for gallon inputs and outputs.

Acre-foot: A water volume equal to one acre of area covered one foot deep.

Conversion factor: The number of US liquid gallons counted as one acre-foot; this converter can use the exact standard factor or the common rounded water-reporting factor.

Cubic feet: A volume unit shown as ft^3; one acre-foot equals 43,560 cubic feet.

Acre-inch: Enough water to cover one acre to a depth of one inch; one acre-foot equals 12 acre-inches.

Million gallons: Gallons divided by 1,000,000, used to make large water volumes easier to read.

Mistake: Entering imperial gallons or dry gallons in Amount .
Fix: Use US liquid gallons when Convert is set to gallons to acre-feet.

Mistake: Leaving words like gallons, AF, or ft^3 inside Amount .
Fix: Enter only the number in Amount , such as 1,000,000 or 2.5.

Mistake: Choosing the wrong direction in Convert and getting a huge or tiny Converted volume .
Fix: If your starting value is gallons, choose gallons to acre-feet; if it is acre-feet, choose acre-feet to gallons.

Mistake: Comparing your answer to a water form that uses 325,851 gallons per acre-foot while Conversion factor is set to the exact factor.
Fix: Change Conversion factor to rounded water-reporting factor when the form asks for 325,851.

Mistake: Setting Round answers to too low and thinking the small difference disappeared.
Fix: Use more decimal places when checking homework, reports, or large water volumes.

• Gallons mean US liquid gallons, not imperial gallons and not dry gallons.
• The exact method uses 325,851.4285714285 US liquid gallons per acre-foot; the rounded method uses 325,851.
• The rounded water-reporting factor can give a slightly different Converted volume, especially for very large volumes.
• The converter handles volume only. It does not account for leakage, evaporation, flow rate, pump runtime, or measurement error.
• Negative water volumes are blocked because they do not make sense for this conversion.
• Very small answers may round to 0 if Round answers to is set too low.

How the conversion is calculated

The calculator first picks the gallons-per-acre-foot factor from Conversion factor. The exact standard factor is derived from standard unit conversions, while the rounded water-reporting factor matches the common 325,851 gallons per acre-foot value used in some water reports [1][2].

acre_feet = gallons / gallons_per_acre_foot

gallons = acre_feet * gallons_per_acre_foot

After the main conversion, the calculator converts the same volume into three check values.

cubic_feet = acre_feet * 43560

acre_inches = acre_feet * 12

million_gallons = gallons / 1000000

Worked example

For 1,000,000 US liquid gallons using the exact factor, the acre-feet result is 1,000,000 / 325,851.4285714285 = 3.068883 acre-feet after rounding to 6 decimal places. The same water is 3.068883 * 43,560 = about 133,680.555556 cubic feet, 3.068883 * 12 = about 36.826599 acre-inches, and 1,000,000 / 1,000,000 = 1 million gallons.

Calculation choices

Rounding is applied only to displayed answers. The internal calculation uses the selected factor before formatting the output. Zero is allowed and returns zero volume outputs while still showing the Factor used.