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Here you will learn about the volume of a cone, including how to calculate the volume of a cone given its radius and perpendicular height and how to calculate a missing length within a cone, given its volume.

Students will first learn about the volume of a cone within geometry in 8 th grade and will extend their learning throughout high school geometry.

The **volume of a cone** is the amount of space inside a cone. A cone is a three-dimensional shape that has a flat surface and a curved surface that joins at a vertex.

The volume of a cone is **one third** of the volume of a cylinder.

The volume of a cone can be calculated using a formula.

To do this, substitute two of the dimensions of the cone into the volume formula, and evaluate the result.

The **volume formula** for any cone is:

\text{Volume}=\cfrac{1}{3} \pi r^2 h

where r is the **radius** of the **base of the cone** and h is the **perpendicular height of the cone.**

For example,

Find the volume of this cone where the radius of the base of the cone is 5 \mathrm{~cm} and the perpendicular height of the cone is 8 \mathrm{~cm}.

You will find the area of the circular base of a cone using A=\pi r^2 (the area of a circle).

Then multiply it by the vertical height, h, and find one third of the answer.

\begin{aligned} \text{Volume}&=\cfrac{1}{3} \pi r^2 h \\\\ &= \cfrac{1}{3} \times \pi \times 5^2 \times 8 \\\\ &=\cfrac{200}{3}\pi \\\\ &=209.4 \, cm^3 \ \text{(1 dp)} \end{aligned}Use this quiz to check your grade 6 to 8 students’ understanding of volume. 10+ questions with answers covering a range of 6th, 7th and 8th grade volume topics to identify areas of strength and support!

DOWNLOAD FREEUse this quiz to check your grade 6 to 8 students’ understanding of volume. 10+ questions with answers covering a range of 6th, 7th and 8th grade volume topics to identify areas of strength and support!

DOWNLOAD FREEA **cone** is a three dimensional object with a circular base that tapers to a point (a vertex). This vertex is also known as the **apex.**

If the apex is directly above the center of the base, the cone is referred to as a **right circular cone.** If the apex is not above the center of the base, this is referred to as an **oblique cone.**

Note: The **slant height** of the cone l is not needed to calculate the volume of a cone, but it is used to calculate the **surface area** of a cone.

**See also:** Surface area of a cone

The volume of cone stays the same if the apex moves parallel to the base but the surface area of the cone changes. This is because the slant heights are not equal for an oblique cone.

How does this relate to 8 th grade and high school math?

**Grade 8: Geometry (8.G.C.9)**Know the formulas for the volumes of cones, cylinders, and spheres and use them to solve real-world and mathematical problems.

**High school: Geometry (HS.G.GMD.A.3)**

Use volume formulas for cylinders, pyramids, cones, and spheres to solve problems.

In order to calculate the volume of a cone:

**Write down the formula: \bf{\textbf{Volume }=\cfrac{1}{3} \, \pi \textbf{r}^2 \textbf{h.}}****Substitute the given values.****Work out the calculation.****Write the final answer, including the units.**

Find the volume of the cone with radius 4 \mathrm{~cm} and perpendicular height 7 \mathrm{~cm}.

Give your answer to 3 significant figures.

**Write down the formula: \bf{\textbf{Volume }=\cfrac{1}{3} \, \pi \textbf{r}^2 \textbf{h.}}**

The formula for the volume of a cone is:

V=\cfrac{1}{3} \pi r^2 h2**Substitute the given values.**

Substitute the values of the radius, r , and the perpendicular height, h , into the formula.

V= \cfrac{1}{3}\times\pi\times{4^2}\times{7}3**Work out the calculation.**

Use a calculator to work out the volume.

V=\cfrac{112}{3}\pi = 117.286…4**Write the final answer, including the units.**

Here you are asked to give the answer to 3 significant figures.

V=117.286 \ldots=117 \mathrm{~cm}^3 \, (3sf)The volume of the cone is 117 \mathrm{~cm}^3 \, (3sf).

Find the volume of the cone with radius 2.1 \mathrm{~cm} and perpendicular height 4.3 \mathrm{~cm}.

Give your answer to 3 significant figures.

**Write down the formula: \bf{\textbf{Volume }=\cfrac{1}{3} \, \pi \textbf{r}^2 \textbf{h.}} **

The volume formula of a cone is:

V=\cfrac{1}{3} \pi r^2 h

**Substitute the given values.**

Substitute the values of the radius, r , and the perpendicular height, h , into the formula.

V= \cfrac{1}{3} \times \pi \times 2.1^2 \times 4.3

**Work out the calculation.**

Use a calculator to work out the volume.

V= 19.8580…

**Write the final answer, including the units.**

Here you are asked to give the answer to 3 significant figures.

V=19.8580 \ldots=19.9 \mathrm{~cm}^3 \, (3sf)

The volume of the cone is 19.9 \mathrm{~cm}^3 \, (3sf).

Calculate the volume of a cone with radius 3 \mathrm{~cm} and perpendicular height 5 \mathrm{~cm}.

Write your answer in terms of \pi.

**Write down the formula: \bf{\textbf{Volume }=\cfrac{1}{3} \, \pi \textbf{r}^2 \textbf{h.}} **

The formula for the volume of a cone is:

V=\cfrac{1}{3} \pi r^2 h

**Substitute the given values.**

Substitute the values of the radius, r , and the perpendicular height, h , into the formula.

V= \cfrac{1}{3} \times \pi \times 3^2 \times 5

**Work out the calculation.**

Because you can change the order of a multiplication and the solution stays the same, we have:

V=\cfrac{1}{3}\times\pi\times{3^{2}}\times{5}=\cfrac{1}{3}\times{3^{2}}\times{5}\times{\pi}

Simplifying this, you get:

V=15\pi

**Write the final answer, including the units.**

Here you need to leave the answer in terms of \pi.

V=15\pi \mathrm{~cm}^3

The volume of the cone is 15 \pi \mathrm{~cm}^3.

Find the volume of the cone with the diameter of 4 \mathrm{~cm} and perpendicular height 6 \mathrm{~cm}.

Write your answer in terms of \pi.

**Write down the formula: \bf{\textbf{Volume }=\cfrac{1}{3} \, \pi \textbf{r}^2 \textbf{h.}} **

The formula for the volume of a cone is:

V=\cfrac{1}{3} \pi r^2 h

**Substitute the given values.**

As the diameter is twice the length of the radius, the radius is equal to 4 \div 2=2 \mathrm{~cm}.

Substitute the values of r and h into the formula to get:

V= \cfrac{1}{3} \times \pi \times 2^2 \times 6

**Work out the calculation.**

Because you can change the order of a multiplication and the solution stays the same, we have:

V=\cfrac{1}{3}\times\pi\times{2^{2}}\times{6}=\cfrac{1}{3}\times{2^{2}}\times{6}\times{\pi}

Simplifying this, you get:

V= 8\pi

**Write the final answer, including the units.**

Here you are asked to leave the answer in terms of \pi.

V=8\pi \mathrm{~cm}^3

The volume of the cone is 8 \pi \mathrm{~cm}^3.

A cone has a volume of 500 \mathrm{~cm}^3 and a radius of 8 \mathrm{~cm}. Calculate the perpendicular height of the cone, correct to 1 decimal place.

**Write down the formula: \bf{\textbf{Volume }=\cfrac{1}{3} \, \pi \textbf{r}^2 \textbf{h.}} **

The volume formula of a cone is:

V=\frac{1}{3} \pi r^2 h

**Substitute the given values.**

You are given the volume and the radius, so substitute these into the formula.

500=\cfrac{1}{3} \times \pi \times 5^2 \times h

As 5^2=25, we have:

500=\cfrac{1}{3} \times \pi \times{25}\times h

**Work out the calculation.**

Solve the equation for h\text{:}

**Write the final answer, including the units.**

Here you are asked to give the answer to 1 decimal place.

h=\cfrac{60}{\pi}=19.1 \mathrm{~cm} \, (1 \, dp)

The perpendicular height of the cone is: 19.1 \mathrm{~cm} \, (\text{to} \, 1 \, \text{dp}) .

A cone has a volume of 800 \mathrm{~cm}^3 and a perpendicular height of 15 \mathrm{~cm}. Calculate the radius of the cone. Give your answer to 2 decimal places.

**Write down the formula: \bf{\textbf{Volume }=\cfrac{1}{3} \, \pi \textbf{r}^2 \textbf{h.}} **

The question involves the volume of a cone, so use the formula for the volume of a cone.

V=\cfrac{1}{3} \pi r^2 h

**Substitute the given values.**

You are given the volume and the perpendicular height, so substitute these into the formula.

800=\cfrac{1}{3} \times \pi \times r^2 \times 15

**Work out the calculation.**

As \cfrac{1}{3} \times 15=5, simplify the right hand side of the equation, before finding the value of r\text{:}

r^2=\cfrac{160}{\pi}

To find the value of r, square root both sides of the equation. By doing this, you get:

r=\sqrt{\cfrac{160}{\pi}}=7.136…

**Write the final answer, including the units.**

Here you are asked to give the answer to 2 decimal places.

r=7.136 \ldots=7.14 \mathrm{~cm} \; (2 \, dp)

The radius of the cone is 7.14 \mathrm{~cm} \; (2 \, dp).

- Using visual representations is a great way for students to grasp what a cone really is. The use of diagrams and real world examples, like an ice cream cone is a way to make the concept relatable.

- Allow students to work through examples on worksheets with a partner or in small groups and have them collaborate on how to answer each question. These conversations can be powerful in deepening student understanding.

- Students can use a volume of a cone calculator or similar technology tool to check their work real time.

**Using the wrong formula**

There are different formulas when finding the volume of different 3D shapes. Using the wrong formula will result in an inaccurate answer. It’s important to be familiar with the different formulas to keep this from happening.

**Not waiting to round the final answer**

It is important to not round the answer until the end of the calculation. This will mean your final answer is accurate.

**Unfamiliar with the difference between the radius and the diameter**

It is important to be familiar with the difference between the radius and diameter, in order to get accurate answers. The diameter is the measure across a circle, and the radius is half of that.

**Using the correct units**

When finding the volume, you will need to use cubic units. For example, cubic inches, cubic feet and cubic inches.

1. Find the volume of a cone of radius 7.3 \mathrm{~cm} and perpendicular height 9.7 \mathrm{~cm}. Give your answer to 3 significant figures.

541 \, cm^3

542 \, cm^3

719 \, cm^3

718 \, cm^3

Substitute the values of r and h into the formula.

\begin{aligned}V&=\cfrac{1}{3} \pi r^2 h \\\\ V&=\cfrac{1}{3}\times \pi \times 7.3^2 \times 9.7 \\\\ V&=541.310… \\\\ V&=541 \ cm^3 \ \text{(3sf)} \end{aligned}

2. Find the volume of a cone of radius 8.6 \mathrm{~cm} and perpendicular height 7.9 \mathrm{~cm}. Write your answer to 3 significant figures.

562 \, cm^3

563 \, cm^3

611 \, cm^3

612 \, cm^3

Substitute the values of r and h into the formula.

\begin{aligned}V&=\cfrac{1}{3}\pi r^2 h \\\\ V&=\cfrac{1}{3}\times \pi \times 8.6^2 \times 7.9 \\\\ V&=611.860… \\\\ V&=612 \ cm^3 \ \text{(3sf)} \end{aligned}

3. Calculate the volume of a cone with the radius 6 \mathrm{~cm} and the perpendicular height 7 \mathrm{~cm}. Write your answer in terms of \pi.

42\pi \, cm^3

84\pi \, cm^3

126\pi \, cm^3

252\pi \, cm^3

To find the volume of a cone, substitute the values of r and h into the formula.

\begin{aligned}V&=\cfrac{1}{3}\pi r^2 h \\\\ V&=\cfrac{1}{3}\times \pi \times 6^2 \times 7 \\\\ V&=84\pi \\\\ V&=84\pi \, cm^3 \end{aligned}

4. A cone has a diameter of 8 \mathrm{~cm} and a perpendicular height of 6 \mathrm{~cm}. Calculate the volume of the cone in terms of \pi.

12\pi \, cm^3

32\pi \, cm^3

48\pi \, cm^3

96\pi \, cm^3

Calculate the value of the radius by dividing the diameter by 2, then substitute the values of r and h into the formula and solve.

r=8 \div 2=4 \mathrm{~cm}

\begin{aligned}V&=\cfrac{1}{3} \pi r^2 h \\\\ V&=\cfrac{1}{3}\times \pi \times 4^2 \times 6 \\\\ V&=32\pi \\\\ V&=32\pi \ cm^3 \end{aligned}

5. A cone has a volume of 400 \mathrm{~cm}^3. The radius of the base is equal to 6 \mathrm{~cm}. Calculate the perpendicular height of the cone to 1 decimal place.

3.5 \mathrm{~cm}

8.2 \mathrm{~cm}

10.6 \mathrm{~cm}

11.1 \mathrm{~cm}

Substitute the volume and the radius into the volume formula and then rearrange to find the perpendicular height, h.

\begin{aligned}&V=\cfrac{1}{3} \pi r^2 h \\\\ &400=\cfrac{1}{3}\times \pi \times 6^2 \times h \\\\ &1200=\pi \times 36 \times h \\\\ &\cfrac{1200}{\pi \times 36}=h \\\\ &h=10.610… \\\\ &h=10.6 \ cm \ \text{(1dp)} \end{aligned}

6. The volume of a cone is 700 \mathrm{~cm}^3. The perpendicular height of a cone is 8 \mathrm{~cm}. Calculate the radius of the cone to 2 decimal places.

5.40 \mathrm{~cm}

5.72 \mathrm{~cm}

9.14 \mathrm{~cm}

9.28 \mathrm{~cm}

Substitute the values of the volume and the perpendicular height into the formula, and rearrange to find the radius r.

\begin{aligned}&V=\cfrac{1}{3} \pi r^2 h \\\\ &700=\cfrac{1}{3}\times \pi \times r^2 \times 8 \\\\ &2100=\pi \times r^2 \times 8 \\\\ &\cfrac{1200}{\pi \times 8}=r^2 \\\\ &r=\sqrt{\cfrac{2100}{\pi \times 8}} \\\\ &r=9.1409… \\\\ &r=9.14 \ cm \ \text{(to 2 dp)} \end{aligned}

Finding the volume of a cone means finding the amount of space within the 3D shape, or how much material or substance can be inside of the shape. It can be thought of as how much water or sand could be inside the cone.

To find the surface area of a cone, you would use the formula, A=\pi r^2+\pi r l, where A is the surface area of the cone, r is the radius of the base of the cone and l is the slant height of the cone.

A frustum of a cone is a geometric solid that is the result of cutting a cone with a plane parallel to its base. It is similar to what you would think of when you cut off the top of a cone. You would be able to calculate the volume and surface area of both solids.

- Surface area
- Pythagorean theorem
- Trigonometry

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