Acre Feet to Gallons Converter

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Convert acre-feet, US liquid gallons, or acres with water depth using a visible gallons-per-acre-foot factor.

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How to use our Acre Feet to Gallons Converter

  1. Choose an option in What do you want to convert? so the calculator shows only the fields that matter.
  2. Enter Water amount (acre-feet), Water amount (gallons), or Area covered (acres) with Water depth and Depth unit.
  3. Open Advanced options if you need to match a report that uses a rounded factor or if you want more decimal places.
  4. Click Calculate and read Converted amount first, then check Amount in gallons, Amount in acre-feet, and Factor used.
  5. Sanity-check the result: 1 acre-foot should be about 325,851 US liquid gallons, and 1 inch over 1 acre should be about one-twelfth of that.
Example inputs for Acre Feet to Gallons Converter
Example inputs for Acre Feet to Gallons Converter

Definitions

Acre-foot: The volume of water made by covering 1 acre of area with water 1 foot deep.

US liquid gallon: The gallon used by this converter; it is not the imperial gallon or the US dry gallon.

Conversion factor: The number of US liquid gallons in 1 acre-foot. The exact setting uses 325,851.428571 gallons per acre-foot.

Common rounded report factor: A shorter factor, 325,851 gallons per acre-foot, often used when whole-gallon reporting is enough.

Water depth: The average depth of water over the whole area, entered in feet or inches.

Acre-inch: The volume made by covering 1 acre with 1 inch of water; it equals one-twelfth of an acre-foot.

Gallons by water depth on 1 acreExact US liquid gallons for common depths from acre-inch up to 1 acre-foot. Use this as a quick check for the area-and-depth mode: gallons scale linearly with acres and depth.Gallons by water depth on 1 acreExact US liquid gallons for common depths from acre-inch up to 1 acre-foot1 in27154 gal6 in162926 gal9 in244389 gal12 in325851 galWater depth on 1 acre
Gallons by water depth on 1 acre
Use this as a quick check for the area-and-depth mode: gallons scale linearly with acres and depth.

Common mistakes and quick fixes

Mistake: Using imperial gallons in Water amount (gallons).
Fix: Enter US liquid gallons only, or convert imperial gallons before using this converter.

Mistake: Leaving What do you want to convert? on Acre-feet to gallons when your known number is gallons.
Fix: Change What do you want to convert? to Gallons to acre-feet so Water amount (gallons) is used.

Mistake: Typing inches in Water depth but leaving Depth unit set to feet.
Fix: Set Depth unit to inches, or divide the inch depth by 12 before entering it as feet.

Mistake: Comparing your answer to a report without checking Conversion factor to use.
Fix: Match Conversion factor to use to the report: exact US liquid gallon math or the common rounded report factor.

Mistake: Thinking Round answers to changes the real math.
Fix: Use Round answers to only for display; the calculation keeps full precision internally.

Mistake: Entering a negative Area covered (acres), Water depth, or Water amount (acre-feet).
Fix: Use zero or a positive number because this converter measures physical water volume.

Limitations & Key Assumptions / Boundary Conditions

  • The converter uses US liquid gallons only. It does not convert imperial gallons or US dry gallons.
  • The area-and-depth mode assumes the Water depth is the average depth across the full Area covered (acres).
  • The exact factor is based on 43,560 square feet per acre, 1 foot of depth, 1,728 cubic inches per cubic foot, and 231 cubic inches per US liquid gallon.
  • The common rounded report factor can differ from exact math by about 0.428571 gallon per acre-foot.
  • Rounding changes the displayed answer only. It does not change the internal calculation.
  • Zero is allowed and returns zero volume. Negative amounts, areas, and depths are blocked because they do not describe a physical water volume here.
  • Very large entries are formatted with commas, but real storage or irrigation measurements may have measurement error that is larger than the shown decimals.

Methodology

Factor used by the converter

The default setting uses exact US liquid gallon math. One acre is 43,560 square feet [1]. Covering that acre 1 foot deep gives 43,560 cubic feet in 1 acre-foot. A cubic foot has 1,728 cubic inches, and a US liquid gallon has 231 cubic inches [2].

gallons_per_acre_foot = 43560 * 1728 / 231

gallons_per_acre_foot = 325851.4285714286

If Conversion factor to use is set to Common water report rounded factor, the converter uses 325,851 gallons per acre-foot instead.

Conversions

For Acre-feet to gallons, the entered Water amount (acre-feet) is multiplied by the selected factor.

gallons = acre_feet * gallons_per_acre_foot

For Gallons to acre-feet, the entered Water amount (gallons) is divided by the selected factor.

acre_feet = gallons / gallons_per_acre_foot

For Acres and depth to gallons, the converter first changes Water depth to feet. If Depth unit is inches, it divides the depth by 12. Then it multiplies Area covered (acres) by depth in feet to get acre-feet.

depth_feet = depth_value for feet, or depth_value / 12 for inches

acre_feet = area_acres * depth_feet

gallons = area_acres * depth_feet * gallons_per_acre_foot

Worked example

For 2.5 acres with 9 inches of water, the depth in feet is 9 / 12 = 0.75 feet. The volume is 2.5 * 0.75 = 1.875 acre-feet. Using the exact factor, gallons = 1.875 * 325,851.4285714286 = 610,971.428571 US liquid gallons.

Rounding and validation

The calculator removes commas and spaces before reading numbers. It blocks blank, nonnumeric, infinite, and negative values. Round answers to changes only the displayed Converted amount, Amount in gallons, and Amount in acre-feet. Factor used is shown so you can see whether exact math or the rounded report factor was applied.

Sources

  1. U.S. Survey Foot: Revised Unit Conversion Factors - NIST
  2. NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity or field of science - NIST