Ft3 to Gallons Calculator: Quick Volume Conversion

This calculator converts cubic feet (ft³) to US gallons instantly. You enter the volume in cubic feet, and it returns the equivalent in gallons, along with liters for metric reference. The conversion is based on the standard factor: 1 cubic foot = 7.48051948 US gallons.

Formula

The conversion is a simple multiplication:

Gallons = Cubic Feet × 7.48051948

Where:

• Cubic Feet (ft³) – the volume you want to convert (input)
• 7.48051948 – the number of US liquid gallons in one cubic foot (constant)
• Gallons (gal) – the resulting volume in US liquid gallons (output)

For metric users, the same volume in liters is: Liters = Cubic Feet × 28.316846592 (since 1 ft³ = 28.316846592 liters).

Worked Example

Using the default value of 10 ft³:

1. Start with 10 ft³.
2. Multiply by the conversion factor: 10 × 7.48051948 = 74.8051948.
3. Round to two decimal places: 74.81 gallons.

For liters: 10 × 28.316846592 = 283.16846592, rounded to 283.17 liters.

So 10 cubic feet equals approximately 74.81 US gallons and 283.17 liters.

Why Convert Cubic Feet to Gallons?

You might need this conversion in several real-world situations:

• Aquariums and fish tanks – tank volumes are often listed in gallons, but dimensions are in feet or inches.
• Water storage – rain barrels, cisterns, or swimming pools measured in cubic feet but filled by the gallon.
• Shipping and freight – cargo volume in cubic feet, but liquid capacity in gallons.
• Home improvement – concrete, soil, or mulch volumes are sold by the cubic foot, but you might want to compare with liquid capacity.
• Fuel or chemical storage – tanks sized in cubic feet but rated in gallons.

US Gallons vs. Imperial Gallons

A common mistake is mixing up US and Imperial (UK) gallons. They are different:

• US gallon = 231 cubic inches = 3.785411784 liters
• Imperial gallon = 277.42 cubic inches = 4.54609 liters

One cubic foot equals 7.4805 US gallons but only 6.2288 Imperial gallons. This calculator uses the US gallon, which is the standard in the United States and for most international liquid measurements in industry. If you need Imperial gallons, multiply your result by 0.832674.

How to Convert Manually (Step-by-Step)

If you don’t have a calculator handy, here’s how to do it by hand:

1. Measure or note the volume in cubic feet.
2. Multiply that number by 7.48051948.
3. The result is the volume in US gallons.

For example, a box that is 2 ft × 3 ft × 4 ft has a volume of 24 ft³. Multiply: 24 × 7.4805 = 179.53 gallons.

To convert gallons back to cubic feet, divide by 7.4805. For instance, 100 gallons ÷ 7.4805 = 13.37 ft³.

Common Mistakes and How to Avoid Them

Here are the pitfalls people often hit:

• Using the wrong gallon – always check whether you need US or Imperial gallons. The difference is about 20%.
• Mixing units – if your dimensions are in inches, convert to feet first (divide by 12) or use a different formula. 1 cubic foot = 1,728 cubic inches.
• Decimal rounding – for large volumes, rounding too early can cause significant errors. Keep at least 4 decimal places until the final step.
• Forgetting that 1 ft³ = 7.48 gallons, not 7.5 – using 7.5 is close but introduces about 0.26% error, which over hundreds of gallons adds up.

Limitations of the Formula

This conversion is exact for pure volume. However, in practice:

• Temperature effects – liquids expand and contract slightly with temperature. The conversion factor assumes standard conditions (60°F / 15.6°C for US gallons).
• Container shape – if you’re measuring a tank, the actual usable volume may be less due to walls, baffles, or sediment.
• Measurement accuracy – your cubic feet input is only as accurate as your length measurements. A 1% error in each dimension becomes a 3% error in volume.

For most everyday uses, the simple multiplication is sufficient. For scientific or engineering work, consider temperature corrections and use more precise constants.

Frequently Asked Questions

How many gallons are in 1 cubic foot?

Exactly 7.48051948 US gallons. For practical purposes, most people round to 7.48 gallons. If you’re using Imperial gallons, it’s 6.2288.

How do I convert cubic feet to gallons for an aquarium?

Measure the tank’s length, width, and height in feet, multiply them together to get cubic feet, then multiply by 7.4805. For example, a 4 ft × 2 ft × 2 ft tank is 16 ft³, which equals 119.68 gallons. Remember to account for glass thickness and substrate if you need the actual water volume.

Is 1 cubic foot of water exactly 7.48 gallons?

Yes, at standard temperature and pressure, 1 cubic foot of water occupies 7.4805 US gallons. The weight of that water is about 62.4 pounds (28.3 kg). This is a handy reference for water weight calculations.

What’s the difference between cubic feet and square feet?

Cubic feet measure volume (length × width × height), while square feet measure area (length × width). You cannot convert directly between them without a third dimension. For example, a floor that is 100 square feet with a 1-foot-deep flood contains 100 cubic feet of water, which is 748 gallons.

How many cubic feet are in a 55-gallon drum?

Divide 55 by 7.4805, which equals approximately 7.35 cubic feet. This is useful when planning storage space for drums.

Can I use this calculator for dry gallons?

No. This calculator uses liquid gallons. Dry gallons (used for grains, produce, etc.) are different: 1 cubic foot = 6.4285 dry gallons. If you’re measuring dry goods, use a different conversion factor.

Related

• Cubic Volume Calculator: Formula & Examples
• Cubic Yard Calculator Diameter: How to Convert
• Cubic Yard Calculator for Cylinder Volume

in ft3 | Volume (cubic feet) | ft³ | 10 | 0
out gal | US Gallons | gal | ft3 * 7.48051948 | 2
out l | Liters | L | ft3 * 28.316846592 | 2