How Many Gallons in One Acre Foot? The Complete US Water Measurement Guide

One acre-foot equals exactly 325,851 gallons of water. This essential US water measurement unit is crucial for agriculture, irrigation, reservoir management, and water rights across the United States. Understanding this conversion helps farmers, engineers, and landowners manage water resources effectively.

325,851
US gallons per acre-foot
Updated: December 21, 2025 Reading time: 5 minutes

Exact Acre-Foot to Gallons Conversion

1
Acre-Foot
=
325,851
US Gallons
≈
1,233.5
Cubic Meters

Based on US Geological Survey and Bureau of Reclamation standards

What is an Acre-Foot of Water?

An acre-foot is a volume measurement used primarily in the United States to quantify large-scale water resources. It represents the volume of water required to cover one acre of land (43,560 square feet) to a depth of one foot.

Visual Explanation

Imagine a football field (excluding end zones). One acre-foot would cover this area with approximately 1 foot of water. Now multiply that volume by 325,851 to get the number of gallons.

Where is Acre-Foot Measurement Used?

  • Agriculture & Irrigation: Water rights allocation and farm irrigation planning
  • Municipal Water Supply: Reservoir capacity and city water planning
  • Pond & Lake Management: Calculating water volumes for recreational ponds
  • Hydrology & Water Rights: Legal water allocation in western US states

Quick Calculation Formula

Gallons = Acre-feet × 325,851
Acre-feet = Gallons ÷ 325,851

Example Calculation:

A 5-acre pond with average 4-foot depth:

5 acres × 4 ft = 20 acre-feet
20 × 325,851 = 6,517,020 gallons

Acre-Foot to Gallons Conversion Table

Acre-Feet US Gallons Equivalent To Common Use Case
0.1 acre-foot 32,585 gallons Small residential pond Garden irrigation seasonal use
1 acre-foot 325,851 gallons Football field 1 ft deep Single-family annual water use
5 acre-feet 1,629,255 gallons Olympic swimming pool (2×) Small farm irrigation
10 acre-feet 3,258,510 gallons 1 acre pond × 10 ft deep Orchard irrigation season
100 acre-feet 32,585,100 gallons 40 Olympic swimming pools Small reservoir capacity
1,000 acre-feet 325,851,000 gallons 400 Olympic swimming pools Municipal water supply

Source: US Bureau of Reclamation Conversion Standards

Calculating Pond Capacity

Example: How many gallons are in a 12-foot deep one-acre pond?

1 acre × 12 feet deep = 12 acre-feet

12 × 325,851 = 3,910,212 gallons

This calculation helps determine fish stocking rates, aeration requirements, and water treatment needs.

Irrigation Water Requirements

Example: A 50-acre farm needs 2 acre-feet/acre for growing season:

50 acres × 2 acre-feet = 100 acre-feet

100 × 325,851 = 32,585,100 gallons

This volume helps farmers plan water rights, storage, and pumping schedules.

Exclusive Insight: Water Measurement Timeline

The acre-foot measurement evolved alongside US westward expansion:

  • 1860s: Mining operations in California first used acre-feet for water management
  • 1902: Bureau of Reclamation standardized acre-foot for irrigation projects
  • 1922: Colorado River Compact allocated water in acre-feet between states
  • Present: Used in 17 western US states for legal water rights

Related US Land Measurement Guides

How Big is an Acre? Visual Examples Square Feet in an Acre (Exact Conversion) Acre to Square Feet Calculator
Acres in a Square Mile Hectares to Acres Conversion Football Field to Acres Comparison

Frequently Asked Questions

One acre-foot contains exactly 325,851 US gallons of water. This is based on the standard definition: 1 acre (43,560 sq ft) covered 1 foot deep.

The exact conversion is 325,851 gallons per acre-foot. This measurement is used extensively in US agriculture, water management, and irrigation planning.

A pond measuring 1 acre in surface area and 12 feet deep contains: 3,910,212 gallons (12 acre-feet × 325,851 gallons/acre-foot).

Acre-foot relates directly to land area and water depth, making it intuitive for irrigation where water application is measured in inches per acre. It's more practical than using millions of gallons for agricultural planning.

1 inch of rainfall over 1 acre = 3,630 cubic feet = approximately 27,154 gallons = 0.0833 acre-foot. So 12 inches (1 foot) of rain = exactly 1 acre-foot.

Western US states use acre-foot extensively: California, Arizona, Colorado, Texas, and Nevada for water rights. Eastern states more commonly use gallons or cubic feet for water measurement.

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