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Secondary 4 · Mathematics
3D shapes · 3D shapes

Volume of a Geometric Solid

Before you start, make sure you know: Measuring volume (Secondary Year 2 (first cycle))
Before you start, make sure you know: The Pythagorean theorem (Secondary Year 2 (first cycle))

A cistern in an apartment building in Santiago, a water tank at a house in La Vega, the reservoir behind a dam like Tavera-Bao: how do we know how much water they can hold? These are all questions about volume: the space a solid takes up. On this page you will learn to calculate it for prisms, pyramids, round solids, and truncated solids.

Units of volume and capacity

Volume is measured in cubic units: $1\text{ cm}^3$ is a little cube with edges 1 cm long. Each unit is 1,000 times the next smaller one, because $10 \times 10 \times 10 = 1{,}000$. When you go from a larger unit to a smaller one (for example, from m³ to dm³) you multiply by 1,000; when you go from a smaller unit to a larger one you divide by 1,000.

Diagram of conversion factors between cubic units of volume and their equivalence with liters and milliliters: from each unit to the next smaller one you multiply by 1,000. m³1 m³ = 1,000 L dm³1 dm³ = 1 liter cm³1 cm³ = 1 ml mm³ ×1,000 ×1,000 ×1,000
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An aquarium is in the shape of a rectangular prism with the following dimensions: $60\text{ cm}$ in length, $30\text{ cm}$ in width and $40\text{ cm}$ in height.…

An aquarium is in the shape of a rectangular prism with the following dimensions: $60\text{ cm}$ in length, $30\text{ cm}$ in width and $40\text{ cm}$ in height. Calculate how many liters of water fit in the aquarium if it is completely filled. (Remember that $1\text{ dm}^3 = 1\text{ liter}$).

60 cm 30 cm 40 cm
Solve

Prisms and cylinders

A prism or a cylinder is a "stack" of identical bases. Its volume is the area of the base times the height:

$$V = A_{base} \times h \qquad \text{Rectangular prism: } V = a \times b \times c \qquad \text{Cylinder: } V = \pi r^2 h$$ Stack of identical disks showing that the volume of a cylinder is the area of the base times the height. stack of identical "coins": V = (area of the base) · height
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A package containing a gaming keyboard is in the shape of a rectangular prism. Its dimensions are $45\text{ cm}$ in length, $15\text{ cm}$ in width and $5\text{ cm}$ in…

A package containing a gaming keyboard is in the shape of a rectangular prism. Its dimensions are $45\text{ cm}$ in length, $15\text{ cm}$ in width and $5\text{ cm}$ in height. Calculate the volume of air inside the box in cubic centimeters.

45 cm 15 cm 5 cm
Solve
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A cylindrical drink can has a diameter of $6\text{ cm}$ and a height of $12\text{ cm}$. Calculate its volume using the value of $\pi \approx 3.14$.

A cylindrical drink can has a diameter of $6\text{ cm}$ and a height of $12\text{ cm}$. Calculate its volume using the value of $\pi \approx 3.14$.

d = 6 cm h = 12 cm
Solve
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Calculate the volume of a prism whose base is a right-angled triangle with legs $6\text{ cm}$ and $8\text{ cm}$, knowing that the height of the prism is $15\text{ cm}$.

Calculate the volume of a prism whose base is a right-angled triangle with legs $6\text{ cm}$ and $8\text{ cm}$, knowing that the height of the prism is $15\text{ cm}$.

8 cm 6 cm h = 15 cm
Solve
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A coffee thermos is cylindrical in shape. The radius of the base measures $4 \text{ cm}$ and the total height is $25 \text{ cm}$. If the thermos is filled to $80 \%$ of…

A coffee thermos is cylindrical in shape. The radius of the base measures $4 \text{ cm}$ and the total height is $25 \text{ cm}$. If the thermos is filled to $80 \%$ of its capacity, how many $150 \text{ ml}$ cups can be completely filled?

(Take $\pi \approx 3.14$ and remember that $1 \text{ dm}^3 = 1 \text{ liter}$).

r = 4 cm 25 cm 80% ? 150 ml
Solve

Pyramids and cones: one third

If you fill a pyramid with water and pour it into a prism with the same base and the same height, you need exactly three pyramids to fill it. The same is true for a cone and a cylinder.

$$V_{pyramid} = \frac{A_{base} \times h}{3} \qquad\qquad V_{cone} = \frac{\pi r^2 h}{3}$$ A prism and a pyramid with the same base and height: three pyramids fill one prism. prism: 1/3 full pyramid × 3= prism
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A decorative glass pyramid has a square base of side $8\text{ cm}$ and a height of $10\text{ cm}$. Calculate the volume of glass needed to manufacture it.

A decorative glass pyramid has a square base of side $8\text{ cm}$ and a height of $10\text{ cm}$. Calculate the volume of glass needed to manufacture it.

8 cm 8 cm h = 10 cm
Solve
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An ice cream cone has the shape of a cone. The radius of the base is $3\text{ cm}$ and its height is $12\text{ cm}$. Calculate how many cubic centimeters of ice cream…

An ice cream cone has the shape of a cone. The radius of the base is $3\text{ cm}$ and its height is $12\text{ cm}$. Calculate how many cubic centimeters of ice cream fit inside it (without overflowing at the top).

r = 3 cm h = 12 cm
Solve
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A decorative glass pyramid has a square base of side $12 \text{ cm}$. If the lateral edge (the segment joining the apex to a vertex of the base) measures…

A decorative glass pyramid has a square base of side $12 \text{ cm}$. If the lateral edge (the segment joining the apex to a vertex of the base) measures $10 \text{ cm}$, calculate the volume of glass contained in the piece.

(Note: you will need to apply Pythagoras' Theorem twice: first to find the diagonal of the base and then to find the height of the pyramid).

h d/2 10 cm 12 cm
Solve

The sphere and the hemisphere

The formula for the volume of a sphere is:

$$V_{sphere} = \frac{4}{3}\pi r^3$$

A hemisphere is half of a sphere (a dome, a bowl), so its volume is half:

$$V_{hemisphere} = \frac{1}{2}\cdot\frac{4}{3}\pi r^3 = \frac{2}{3}\pi r^3$$

Since the radius is cubed, if you double the radius the volume is multiplied by $2^3 = 8$.

Three small balls of radius 3 are melted into one ball of radius approximately 4.33. → 3 balls of r = 31 ball of R ≈ 4.33
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The PE teacher stores handball balls in a box. If each ball has a radius of $9\text{ cm}$, calculate the volume of one of them rounding to two decimal places. (Use…

The PE teacher stores handball balls in a box. If each ball has a radius of $9\text{ cm}$, calculate the volume of one of them rounding to two decimal places. (Use $\pi \approx 3.14$).

r = 9 cm
Solve
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An ice cream cone is to be made whose slant height measures $15 \text{ cm}$ and whose base radius is $6 \text{ cm}$. Calculate the volume of ice cream that fits inside…

An ice cream cone is to be made whose slant height measures $15 \text{ cm}$ and whose base radius is $6 \text{ cm}$. Calculate the volume of ice cream that fits inside the cone. If a perfect hemisphere of ice cream of the same radius is added on top of the base when served, what will be the total volume of the ice cream?

r=6 h r=6 g=15
Solve
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Three metal balls of radius $3 \text{ cm}$ are melted down to create a single larger sphere. Assuming no material is lost in the process, what will be the radius of the…

Three metal balls of radius $3 \text{ cm}$ are melted down to create a single larger sphere. Assuming no material is lost in the process, what will be the radius of the resulting new sphere? Round the answer to two decimal places.

r = 3 cm Melting R = ? 3 · V₁ = V₂
Solve
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A lead sphere with a radius of $10\text{ cm}$ is melted down to manufacture small cylinders with a diameter of $2\text{ cm}$ and a height of $3\text{ cm}$. Assuming that…

A lead sphere with a radius of $10\text{ cm}$ is melted down to manufacture small cylinders with a diameter of $2\text{ cm}$ and a height of $3\text{ cm}$. Assuming that $5\%$ of the material is lost in the smelting process, how many complete cylinders can be made? If each cylinder has a mass of $107\text{ g}$, what is the density of the lead used in $g/cm^3$?

R=10 cm density = ? −5% loss d=2 cm h=3 cm n = ? m = 107 g
Solve

Composite solids

Many real objects combine several solids: a rice silo (cylinder + cone), a capsule (cylinder + two hemispheres), a piece with a hole. You break them down, calculate each part, and add the volumes (or subtract the empty spaces).

The regular octahedron

A regular octahedron with edge $a$ breaks down into two identical square pyramids joined at their bases. The base is a square with side $a$ and area $a^2$. The height of each pyramid comes from the Pythagorean theorem: half the diagonal of the base is $\frac{a\sqrt{2}}{2}$ and the lateral edge is $a$, so $h = \sqrt{a^2 - \frac{a^2}{2}} = \frac{a\sqrt{2}}{2}$.

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A cylindrical glass with an internal diameter of $6 \text{ cm}$ contains water up to a height of $10 \text{ cm}$. An irregularly shaped stone is placed inside it and the…

A cylindrical glass with an internal diameter of $6 \text{ cm}$ contains water up to a height of $10 \text{ cm}$. An irregularly shaped stone is placed inside it and the water level rises to $12.5 \text{ cm}$ without overflowing. What is the volume of the stone expressed in cubic centimeters?

Solve
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Calculate the volume of a geometric solid formed by a cylinder of height $10 \text{ cm}$ and radius $4 \text{ cm}$, topped by a square pyramid whose base is inscribed in…

Calculate the volume of a geometric solid formed by a cylinder of height $10 \text{ cm}$ and radius $4 \text{ cm}$, topped by a square pyramid whose base is inscribed in the circle of the cylinder and whose height is $6 \text{ cm}$.

(Hint: the side of the square base of the pyramid is equal to the side of a square inscribed in a circle of radius $4 \text{ cm}$).

h₂ = 6 h₁ = 10 r = 4
Solve
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A municipality has installed concrete planters in the shape of a regular hexagonal prism. If each side of the base hexagon measures $30 \text{ cm}$ and the height of the…

A municipality has installed concrete planters in the shape of a regular hexagonal prism. If each side of the base hexagon measures $30 \text{ cm}$ and the height of the planter is $60 \text{ cm}$, calculate the volume of soil (in liters) needed to fill it completely.

(Given: remember that you must first find the apothem of the base using the Pythagorean Theorem).

a 30 15 SOIL H = 60 cm L = 30 cm
Solve
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A grain silo has a composite shape: a central cylindrical section with a height of $12\text{ m}$ and a diameter of $4\text{ m}$, topped at the upper part by a hemisphere…

A grain silo has a composite shape: a central cylindrical section with a height of $12\text{ m}$ and a diameter of $4\text{ m}$, topped at the upper part by a hemisphere and at the lower part by a discharge cone with a height of $3\text{ m}$. Calculate the total capacity of the silo in cubic meters. If the silo is filled to $85\%$ of its capacity, how many metric tons of wheat will it contain if the density of wheat is $750\text{ kg/m}^3$?

r
Solve

Frustums of pyramids and cones

A truncated solid is obtained by cutting a pyramid or a cone with a plane parallel to the base and removing the tip. What is left is a frustum, with two parallel bases: the larger one ($A_1$) and the smaller one ($A_2$). Many water tanks, cups, and buckets have this shape, and reservoirs are also modeled this way, layer by layer.

A complete cone with its tip cut off by a plane parallel to the base: what remains is a frustum of a cone of height h. h tip removed frustum larger base A₁

First method: difference of similar cones (or pyramids). The small cone we remove is similar to the large one, with ratio $k$ between their measurements. You calculate the volume of the complete solid and subtract the volume of the tip.

Second method: formula.

$$V_{frustum} = \frac{h}{3}\left(A_1 + A_2 + \sqrt{A_1 A_2}\right)$$

For a frustum of a cone, $A_1 = \pi R^2$ and $A_2 = \pi r^2$, and this becomes $V = \dfrac{\pi h}{3}(R^2 + r^2 + Rr)$.

Why it works: the formula comes from subtracting two similar solids. Since the volumes of similar solids are in the ratio $k^3$, the subtraction gives a factor $(1 - k^3)$ that factors and produces the sum $A_1 + A_2 + \sqrt{A_1A_2}$.

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A water tank is in the shape of a frustum of a cone. The radius of the larger base is $3 \text{ m}$, the radius of the smaller base is $1.5 \text{ m}$ and the height of…

A water tank is in the shape of a frustum of a cone. The radius of the larger base is $3 \text{ m}$, the radius of the smaller base is $1.5 \text{ m}$ and the height of the tank is $4 \text{ m}$. Calculate the capacity of the tank in cubic meters.

(Hint: you can use the formula for the volume of a frustum of a cone or view it as the difference between two cones).

h = 4 m R = 3 m r = 1.5 m
Solve
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A street furniture design company has designed a concrete litter bin in the shape of a frustum of a regular square pyramid. The external dimensions of the upper base are…

A street furniture design company has designed a concrete litter bin in the shape of a frustum of a regular square pyramid. The external dimensions of the upper base are $40\text{ cm}$ on each side, those of the lower base are $30\text{ cm}$ on each side, and the total height is $80\text{ cm}$. To make it functional, the interior is hollow with the same shape, but leaving walls of a constant thickness of $5\text{ cm}$ on the sides and on the bottom base (the top is open). Calculate the volume of concrete needed to manufacture each litter bin in cubic decimeters ($dm^3$).

40 cm 30 cm thickness = 5 cm H=80
Solve

More complex problems

In hard problems, several ideas are combined. A strategy (Pólya's method): understand the solid and its data, plan how to break it down, carry out the calculations with consistent units, and check whether the result makes sense.

  • When there is material with thickness (walls), calculate the outer volume and subtract the inner one; remember to reduce the inner dimensions.

  • When a solid is melted down to make others, the volume is conserved (minus any losses, if there are any).

  • With similarity: if the linear measurements are multiplied by $k$, the volume is multiplied by $k^3$. So a cone filled to half its height has a volume of $\left(\tfrac{1}{2}\right)^3 = \tfrac{1}{8}$ of the whole cone.

  • Density: mass = density × volume.

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A sculptor wishes to create a stainless steel piece consisting of a cube with an edge length of $20\text{ cm}$ from which eight tetrahedra have been removed at its…

A sculptor wishes to create a stainless steel piece consisting of a cube with an edge length of $20\text{ cm}$ from which eight tetrahedra have been removed at its corners. Each tetrahedron is formed by connecting a vertex of the cube to the midpoints of the three edges that meet at that vertex (a midpoint truncation). Determine the final volume of the sculpture. What percentage of the original cube's volume has been removed?

L = 20 cm Cubo con 8 vértices eliminados
Solve
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An hourglass consists of two identical cones joined at their vertices inside a protective glass cylinder. The cones have a base radius of $6\text{ cm}$ and a height of…

An hourglass consists of two identical cones joined at their vertices inside a protective glass cylinder. The cones have a base radius of $6\text{ cm}$ and a height of $10\text{ cm}$. If the upper chamber is filled with sand up to half its height, calculate the volume of sand in $cm^3$. If the sand flows into the lower chamber at a constant rate of $5\text{ cm}^3$ per minute, how long will it take for the upper part to empty? (Remember to use similar cones to find the radius of the sand's surface).

6 cm r = ? 10 cm h/2 5 cm³/min
Solve
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Cavalieri's Principle states that if two solids have the same height and the area of their cross-sections at any height is equal, then they have the same volume. Use…

Cavalieri's Principle states that if two solids have the same height and the area of their cross-sections at any height is equal, then they have the same volume. Use this idea to compare the volume of a sphere of radius $R$ with the volume contained between a cylinder of radius $R$ and height $2R$, and a double cone inscribed in it. Show mathematically that the volume of the sphere is indeed $V = \frac{4}{3}\pi R^3$ by first calculating the volume of the cylinder and subtracting that of the two cones.

A₁ = A₂ 2R R R h r Cylinder - Double Cone Sphere A₁ = πR² - πh² A₂ = πr² = π(R² - h²)
Solve
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A perfume bottle has the shape of a regular octahedron with an edge length of $6\text{ cm}$. However, the glass has a thickness of $2\text{ mm}$ on all its faces. The…

A perfume bottle has the shape of a regular octahedron with an edge length of $6\text{ cm}$. However, the glass has a thickness of $2\text{ mm}$ on all its faces. The manufacturer claims that the container can hold $80\text{ ml}$ of fragrance ($1\text{ ml} = 1\text{ cm}^3$). Perform the necessary calculations to check whether the claim is true. (Given: The volume of an octahedron with edge length $a$ is $V = \frac{\sqrt{2}}{3} a^3$. You must consider how the thickness affects the edge length of the interior cavity).

a = 6 cm Thickness: 2 mm Problem data: • Ext. edge = 6 cm • Thickness = 2 mm • Claim: V = 80 ml Volume of Octahedron: V = (√2 / 3) a³
Solve
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A metal piece in the shape of a regular hexagonal pyramid is to be submerged in a cylindrical container of radius $15\text{ cm}$ containing water. The pyramid has a base…

A metal piece in the shape of a regular hexagonal pyramid is to be submerged in a cylindrical container of radius $15\text{ cm}$ containing water. The pyramid has a base edge of $10\text{ cm}$ and a lateral edge of $20\text{ cm}$. When the piece is fully submerged, by how many millimeters will the water level rise in the container? (Remember that you must first calculate the height of the pyramid using Pythagoras' Theorem twice).

20 cm 10 cm h ap s r = 15 cm Δh = ?
Solve

Back to the beginning: a rectangular cistern measuring $2 \times 1.5 \times 1.2$ m holds $3.6\text{ m}^3 = 3{,}600$ L, about 951 gallons; and if the tank is a frustum of a cone, we use the frustum formula.

Summary

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