Area to Gallons Calculator: How to Convert

This calculator converts an area (in square feet, square meters, etc.) into gallons, assuming a uniform depth or height of liquid. You enter the area, the depth, and choose the unit system; it returns the volume in US gallons (and liters). The formula is simple: Volume = Area × Depth, then convert cubic units to gallons.

Formula

The calculator uses the basic volume formula:

V = A × h

• V = volume (cubic feet, then converted to gallons)
• A = area of the base (square feet)
• h = depth or height (feet, converted from inches)

Since 1 cubic foot = 7.48052 US gallons, the final step multiplies the cubic feet by that factor. If you work in metric, 1 cubic meter = 1000 liters, and 1 liter = 0.264172 US gallons.

Worked Example

Using the default values: area = 100 sq ft, depth = 6 inches.

1. Convert depth to feet: 6 in ÷ 12 = 0.5 ft
2. Volume in cubic feet: 100 sq ft × 0.5 ft = 50 cu ft
3. Convert to gallons: 50 × 7.48052 = 374.026 gallons

The calculator rounds to one decimal, so it shows 374.0 US gallons (and 1415.8 liters).

When to Use an Area-to-Gallons Conversion

This type of calculation is common for:

• Filling a rectangular pool, pond, or aquarium to a certain depth
• Estimating water needed for a garden bed or flood irrigation
• Calculating the capacity of a flat-bottomed tank or container
• Mixing a solution (e.g., fertilizer) over a given area at a set depth

It works for any shape as long as the depth is uniform and the area is known. For irregular shapes, you may need to approximate the area or break it into smaller rectangles.

Common Mistakes and How to Avoid Them

• Unit mix-ups: Mixing inches with feet, or square feet with square meters, is the most common error. Always convert all measurements to the same unit system first.
• US vs. Imperial gallons: The calculator gives US gallons. Imperial gallons are about 20% larger (1 Imperial gallon = 1.20095 US gallons). Check which your context requires.
• Depth vs. height: For a container that is not a simple box, the depth may vary. This formula only works for uniform depth.
• Rounding too early: Round only at the end, not during intermediate steps, to avoid significant error.

Limitations of the Formula

This calculation assumes a flat, horizontal bottom and vertical sides. Real-world containers often have sloped sides, rounded corners, or irregular shapes. In those cases, the formula overestimates or underestimates the true volume. For example, a typical above-ground pool with sloped walls holds less than a straight-sided box of the same top area and depth. Also, the formula gives the total volume, not the usable volume if you need to leave headroom or if the container has internal obstructions.

Alternatives and Related Calculations

If you have a cylindrical tank, use the cylinder volume formula (π × r² × h). For a spherical tank, use (4/3) × π × r³. If you know the weight of water, remember that 1 US gallon of water weighs about 8.34 pounds (3.78 kg) at room temperature. For soil or mulch, you might need cubic yards instead of gallons; 1 cubic yard = 202.0 US gallons.

Frequently Asked Questions

How many gallons are in a square foot?

A square foot by itself has no volume. If you fill a square foot area to a depth of 1 inch, that’s 0.6234 US gallons (7.48052 ÷ 12). To get gallons, you must specify a depth.

How do I convert square meters to gallons?

First convert square meters to square feet (1 m² = 10.7639 ft²), or work in metric: multiply area (m²) by depth (m) to get cubic meters, then multiply by 264.172 to get US gallons. For example, 10 m² at 0.1 m depth = 1 m³ = 264.2 gallons.

What is the difference between US and Imperial gallons?

A US gallon is 231 cubic inches (3.785 liters). An Imperial gallon is 277.42 cubic inches (4.546 liters), used mainly in the UK and some Commonwealth countries. The difference is about 20%.

Can I use this for a pool with a deep end?

No, not directly. For a pool with varying depth, calculate the average depth (shallow + deep ÷ 2) and multiply by the surface area. That gives a good approximation for rectangular pools.

How many gallons of water does it take to cover 1 acre 1 inch deep?

One acre is 43,560 square feet. At 1 inch deep, that’s 43,560 × (1/12) = 3,630 cubic feet, which equals 27,154 US gallons (3,630 × 7.48052). This is a standard unit called an “acre-inch.�

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in a | Area | sq ft | 100 | 0
in d | Depth | in | 6 | 0
out gal | Volume | US gal | a * (d / 12) * 7.48052 | 1
out l | Volume | liters | a * (d / 12) * 28.3168 | 1