# 3 ways to calculate cubic feet

A "cubic measure" is a three-dimensional measure of volume. If you have a cubic measurement in a different unit, you can easily convert it to cubic feet. You can also find the volume of common shapes, such as rectangular prisms and cylinders, in just a few steps. Regardless of whether you have a math problem or want to find the volume of a space like a room or a posthole, the process is the same: just multiply the area of the base by the height. Also note that cubic feet can be written as feet.3.

## Steps

### Method 1 of 3: Convert to Cubic Feet

#### Step 1. Divide by 1728 to convert cubic inches to cubic feet

If you measured a shape or space in inches or were given units in inches, it is easy to convert them to feet. Keep in mind that inches are smaller units, so there will be fewer cubic feet than cubic inches. Just take the volume in cubic inches and divide it by 1728.

### For example, if the volume is 6912 cubic inches, divide that number by 1728, which results in 4. Therefore, the volume is 4 cubic feet

#### Step 2. Multiply by 27 to convert cubic yards to cubic feet

If you measured in yards instead of feet, all you need to do is multiply the volume by 27. Remember that yards are units larger than feet, so you will have more cubic feet than cubic yards.

### For example, if the volume of the measured shape or space is 1000 cubic yards, multiply 1000 by 27, which results in 27,000 cubic feet

#### Step 3. Divide by 28,316,85 to convert cubic centimeters to cubic feet

Even if centimeters are metric units and feet are imperial units, you can still convert between the two. Centimeters are smaller units than feet, so you will have more cubic centimeters than cubic feet. Start with the volume in cubic centimeters and divide it by 28,316,85.

### For example, if the volume of the shape or space is 500,000 cubic inches, divide this number by 28,316.85. This equates to 17.6573312356, which can be rounded to 17.66 cubic feet

#### Step 4. Multiply by 35.31 to convert cubic meters to cubic feet

Converting between metric and imperial units is not as complicated as you might think. To change the measurement from the largest cubic meters to the smallest units of cubic feet, multiply by 35, 31.

### Method 2 of 3: Finding the Volume of a Rectangular Prism

#### Step 1. Note that the formula for the volume of a rectangular prism is V = Bh

Square shapes (cubes) and rectangular shapes are considered rectangular prisms. In this formula, V is the volume, B is the area of the base, and H is the height. Just multiply the area of the base by the height to find the volume.

### Use the same units for each side of the prism. Ideally, measure in feet so that the result is in cubic feet. Otherwise, you can convert the units after finding the volume

#### Step 2. Find the area of the base by multiplying the length by the width

To find the area of a rectangle, you must know the length (L) and the width (W). Measure each side or check the diagram if the numbers were provided. To find the area of the base of a rectangular prism, multiply the length by the width.

• For example, suppose the length of a room you measure is 10 feet and the width of a room is 5 feet. Multiply 10 by 5, which gives 502.
• The feet are squared because you are not only multiplying the numbers, but also the units.

#### Step 3. Multiply the area of the base by the height to find the volume

Now that you know the area of the base, measure the height or refer to the diagram if one was provided. Multiply the area of the base by the height to finish the formula.

• For example, if the height of the room is 15 feet, multiply 15 by 50 feet2 (the area of the base of the room that you found in the previous step). The total volume of the room is 750 feet3.

### Method 3 of 3: Calculate the Volume of a Cylinder

#### Step 1. Use the formula V = Bh to find the volume of a cylinder

In this formula, V is the volume; B, the area of the base; and h, the height. All you have to do is multiply the area of the base times the height to find the volume of the cylinder.

### Measure the space or shape in feet, or convert all units to feet before you begin so your answer is in cubic feet. Otherwise, convert the units to cubic feet when you know the volume

Step 2. Find the area of the base using the formula πr2.

Consult the diagram to find the number given by the radius (r) or measure it if you have a shape or three-dimensional space. Since the base is a circle, find the area by squaring the radius and multiplying it by π, which equals 3.14.

• For example, if you are digging a hole to install a pole and the radius of the pole is 0.5 feet, multiply this number by 0.5 to give 0.25 feet.2. Then multiply 0.25 feet2 times 3.14, which results in 0.785 feet2.
• Remember that the units for the radius are squared because you multiply them together in the same way that you multiply the figures.
• If you know the diameter of the circle instead of the radius, simply divide the diameter by 2 to give the radius. Therefore, the radius of a circle with a diameter of 12 would be 6.

#### Step 3. Multiply the area of the base by the height to find the volume

Measure the height of the cylinder or refer to the diagram if the numbers were provided. Then just multiply the height by the area of the base.

• For example, take the area of the last step, which is 0.785 feet.2. If you want the post hole to be about 2 feet deep, the height would be 2, so multiply this number by 0.785 feet.2 so that it comes out 1.57 feet3, figure that would be the volume of the hole.