Cubic Feet to Gallons Calculator

Converting cubic feet to gallons is straightforward once you know the right multiplier. One cubic foot holds approximately 7.48052 US gallons. So if you know the volume of a space or container in cubic feet, you multiply by that number and you're done.

The tricky part for most people is getting the cubic footage right in the first place. For a rectangular container, that's just length × width × height (all measured in feet). For irregular shapes, you might need to break the volume into simpler sections and add them up.

A few things worth keeping in mind:

• Make sure all your measurements are in feet before you multiply. Mixing inches and feet is the most common source of errors.
• This conversion applies to liquid volume, so it's most useful for tanks, pools, reservoirs, and similar containers.
• The result is in US gallons by default. If you need imperial gallons, the multiplier is different (more on that below).

Once you've got your cubic feet figure, the math is just one step. It really is that simple.

The formula is:

Gallons = Cubic Feet × 7.48052

That number, 7.48052, comes from the definition of a US liquid gallon. One gallon equals exactly 231 cubic inches. Since one cubic foot contains 1,728 cubic inches, dividing 1,728 by 231 gives you 7.48052. It's not a round number, but it's precise.

For most everyday purposes, rounding to 7.48 is perfectly fine. If you're calculating the capacity of a large tank or a commercial reservoir, using the full 7.48052 keeps your numbers tighter.

A couple of quick examples:

• 1 cubic foot × 7.48052 = 7.48 gallons
• 5 cubic feet × 7.48052 = 37.40 gallons
• 10 cubic feet × 7.48052 = 74.81 gallons

Going the other direction is just as easy. To convert gallons back to cubic feet, divide by 7.48052. So 100 gallons ÷ 7.48052 = about 13.37 cubic feet.

Not all gallons are the same, and that distinction matters more than people realize. The US gallon and the imperial gallon are genuinely different units, and using the wrong one can throw off your calculations by nearly 20 percent.

The imperial gallon is used in the United Kingdom, Canada (for some applications), and several other countries. It's about 20% larger than a US gallon. So if you're converting cubic feet for a UK-based project or working with a product spec that lists imperial gallons, you'd multiply cubic feet by 6.22884 instead.

In the United States, when someone says "gallon" they almost always mean the US liquid gallon. That's the standard for fuel, water volume, aquariums, and virtually every consumer application. When in doubt, confirm which gallon the spec is referencing before you run the numbers.

Here are some conversions you're likely to run into. These use the standard US gallon multiplier of 7.48052.

• 0.5 ft³ = 3.74 gallons
• 1 ft³ = 7.48 gallons
• 2 ft³ = 14.96 gallons
• 3 ft³ = 22.44 gallons
• 5 ft³ = 37.40 gallons
• 10 ft³ = 74.81 gallons
• 15 ft³ = 112.21 gallons
• 20 ft³ = 149.61 gallons
• 25 ft³ = 187.01 gallons
• 50 ft³ = 374.03 gallons
• 100 ft³ = 748.05 gallons

These numbers come up constantly in real situations. A small chest freezer, for example, might be around 5 cubic feet. A standard bathtub holds roughly 2.5 to 3 cubic feet of water. A 10-foot by 10-foot room with 8-foot ceilings has 800 cubic feet of air volume, which sounds wild when you convert it (about 5,984 gallons), but that's how the math works.

This chart covers a wide range of values so you can look up common conversions at a glance without pulling out a calculator every time.

If your value falls between rows, just multiply your cubic feet number by 7.48052 for US gallons or 6.22884 for imperial gallons. The chart is a quick reference, not a replacement for the formula when you need precision.

Two of the most common reasons people look up cubic feet to gallon conversions are water tanks and aquariums. Both involve rectangular or near-rectangular containers, so the math is pretty clean.

For a rectangular water tank, measure the interior dimensions in feet (length, width, depth), multiply them together to get cubic feet, then multiply by 7.48052. So a tank that's 4 feet long, 2 feet wide, and 2 feet deep holds 4 × 2 × 2 = 16 cubic feet, which is about 119.7 gallons.

For aquariums, the process is the same, though most tanks are measured in inches. Convert inches to feet first by dividing by 12. A standard 55-gallon aquarium, for instance, is typically 48" × 13" × 21". Converting: 4 ft × 1.083 ft × 1.75 ft = 7.58 cubic feet × 7.48052 = roughly 56.7 gallons. (Slightly over the rated capacity, which accounts for the glass thickness and the fact that you never fill a tank to the absolute brim.)

A few practical notes for these use cases:

• Water tanks: Always calculate based on interior dimensions, not exterior. Tank walls take up space.
• Aquariums: Subtract about 10 to 15 percent from the calculated volume to account for gravel, decorations, and the water line being below the top edge.
• Cylindrical tanks: Use the formula π × r² × h to get cubic feet, then multiply by 7.48052. For a tank with a 1.5-foot radius and a 4-foot height, that's 3.14159 × 2.25 × 4 = 28.27 cubic feet, or about 211.6 gallons.

Getting these numbers right upfront saves a lot of headache later, especially when you're buying a pump, planning a water treatment system, or figuring out how much conditioner to add to an aquarium.

If you want to work through a conversion manually, here's a reliable process you can follow for any container shape.

1. Measure the container. Get length, width, and height (or depth) in the same unit. Inches, feet, meters, whatever you have. Consistency is what matters.
2. Convert all measurements to feet. Divide inches by 12. Divide centimeters by 30.48. This step is where most errors happen, so double-check it.
3. Calculate cubic feet. For a rectangular container: length × width × height. For a cylinder: π × radius² × height. For irregular shapes, break it into sections and add the results.
4. Multiply by 7.48052. This converts cubic feet to US gallons. Use 6.22884 if you need imperial gallons.
5. Adjust for real-world conditions. If you're calculating usable capacity (not theoretical maximum), subtract a percentage for displacement from objects inside or for a fill level below the top.

That's really all there is to it. The formula never changes. The only variable is making sure your starting measurements are accurate and in the right units before you do anything else.

It might seem like a few gallons off here or there wouldn't be a big deal. In some cases, that's true. In others, the difference is significant.

For water storage and emergency preparedness, knowing your actual tank capacity determines how long your supply will last. Overestimating by even 20 percent could leave you short at the wrong time.

For aquariums, dosing medications and water conditioners is based on volume. Too little and the treatment doesn't work. Too much and you can harm the fish. Getting the gallon count right isn't optional.

In construction and plumbing, accurate volume calculations affect pipe sizing, pump selection, and system pressure. An undersized pump on an oversized tank means poor performance and premature wear.

For agriculture and irrigation, tank capacity directly affects scheduling. Farmers and growers who miscalculate their storage volume end up either over-irrigating or running dry during critical growth periods.

The math itself is easy. The multiplier is fixed. The real discipline is taking accurate measurements before you start and making sure you're using the right type of gallon for your application. Get those two things right and the rest follows naturally.