How to Convert Cubic Feet to Gallons

This guide shows you how to convert a volume measured in cubic feet (ft³) into gallons (gal), a common need when sizing aquariums, water tanks, fuel storage, or shipping containers. You’ll learn the exact conversion factor, how to apply it step by step, and how to avoid the unit mix-ups that cause most errors. No special tools are needed—just a calculator or even pen and paper.

Formula

The conversion is straightforward: 1 cubic foot equals 7.48052 US gallons. To convert a volume from cubic feet to gallons, multiply the number of cubic feet by this factor.

In symbols: Gallons = Cubic Feet × 7.48052

Where:

• Cubic Feet (ft³) – the volume you want to convert
• 7.48052 – the conversion factor (gallons per cubic foot, US liquid)
• Gallons (gal) – the resulting volume in US liquid gallons

If you’re dealing with a rectangular container, first calculate its volume in cubic feet: Volume (ft³) = Length (ft) × Width (ft) × Height (ft). Then apply the conversion factor.

Worked Example

Using the default values from the calculator above: a box that is 4 feet long, 2 feet wide, and 1 foot high.

Step 1: Calculate cubic feet.
4 ft × 2 ft × 1 ft = 8 ft³

Step 2: Multiply by the conversion factor.
8 ft³ × 7.48052 = 59.84416 gallons

Step 3: Round to two decimal places.
59.84 gallons

The calculator gives the same result: 59.84 gallons.

When to Use This Conversion

Convert cubic feet to gallons whenever you have a volume measured in cubic feet but need to know how many gallons it holds—for example, filling a fish tank, estimating water in a pool, checking fuel tank capacity, or planning irrigation storage. It’s also useful when reading product specs: some labels give volume in cubic feet, while pumps or containers are rated in gallons.

How to Read the Result

The result is the volume in US liquid gallons. This is the standard gallon used in the United States for liquids like water and fuel. If you need imperial gallons (used in the UK and some Commonwealth countries), note that 1 cubic foot equals 6.22884 imperial gallons—a different factor. Always confirm which gallon your application uses.

Common Mistakes

• Using the wrong gallon type: Mixing up US and imperial gallons is the most common error. The factor 7.48052 is for US gallons; imperial gallons require 6.22884.
• Forgetting to convert all dimensions to feet: If you measure length in inches and width in feet, your cubic feet number will be wrong. Convert every dimension to feet first (divide inches by 12).
• Rounding too early: Rounding the cubic feet value before multiplying can throw off the final gallon figure, especially for large volumes. Keep full precision until the final step.
• Confusing volume with capacity: The conversion assumes the container is completely full. If there’s air space, the actual liquid volume will be less.

Tips

• Use the calculator above for quick checks—just enter length, width, and height in feet.
• For irregular shapes, break them into rectangular sections, calculate each, then add the gallon totals.
• If you’re working in metric, convert meters to feet first (1 m = 3.28084 ft) or use the direct factor: 1 m³ = 264.172 gallons.
• For water applications, remember that 1 US gallon of water weighs about 8.34 pounds, so you can estimate weight from volume if needed.

Troubleshooting

My result seems too large or too small. Double-check your measurements. A common issue is using inches instead of feet—for example, 12 inches is 1 foot, not 12 feet. Also verify the gallon type: US vs. imperial.

The calculator shows an error. Make sure all inputs are positive numbers. If you see “Cannot compute,� it means one of your values is negative or zero, which isn’t valid for a physical volume.

My container isn’t rectangular. For cylinders, use the formula π × r² × h (in feet) to get cubic feet, then multiply by 7.48052. For spheres, use (4/3) × π × r³.

I need imperial gallons. Simply multiply your cubic feet by 6.22884 instead of 7.48052. If you’re using the calculator, you’ll need to do that step manually after getting the cubic feet output.

Frequently Asked Questions

How many gallons are in 1 cubic foot?

Exactly 7.48052 US gallons. For imperial gallons, it’s 6.22884.

Can I convert gallons back to cubic feet?

Yes, divide the number of gallons by 7.48052 to get cubic feet. For example, 10 gallons ÷ 7.48052 = 1.3368 ft³.

Is the conversion the same for all liquids?

Yes, the conversion factor is based on volume, not the type of liquid. One cubic foot of water, oil, or milk all equal 7.48052 US gallons.

Why are there different gallons?

Historically, the US and UK defined gallons differently. The US gallon is based on a wine gallon, while the imperial gallon is based on a beer gallon. They differ by about 20%.

How do I convert cubic feet to gallons for a cylindrical tank?

First find the volume in cubic feet: π × (radius in ft)² × height in ft. Then multiply by 7.48052.

What if my measurements are in inches?

Convert inches to feet by dividing by 12 before calculating volume. For example, 24 inches = 2 feet. Then proceed as usual.

Related

• Cubic Feet to Gallons Calculator: Convert Volume
• 64 oz to Gallons Calculator and Conversion Guide
• 128 oz to Gallons Calculator and Conversion Guide

in l | Length | ft | 4 | 0 | 100000
in w | Width | ft | 2 | 0 | 100000
in h | Height | ft | 1 | 0 | 100000
out gal | Volume | gal | l * w * h * 7.48052 | 2
out ft3 | Volume | ft³ | l * w * h | 2