How to Find the Volume of a Cylinder, Cone, and Sphere

Volume is “how much fits inside” — water in a tank, popcorn in a cone, air in a balloon. Three formulas cover most of what you’ll meet in middle school, high school, and on the SAT. Here’s the no-stress way to remember them.

We’ll also cover prisms, pyramids, and composite solids, because the SAT and ACT love combining shapes (a cylinder with a cone on top, for example). Once you understand the building blocks, composite solids are just addition.

Cylinder

A cylinder is a tube — two circles connected by straight sides.

$$V = \pi r^2 h$$

Where $r$ is the radius of the base and $h$ is the height.

Example: a can with radius 3 cm and height 10 cm has volume $\pi(3)^2(10) = 90\pi \approx 282.7\,\text{cm}^3$.

Think of it as “area of the base × height.” That single idea works for any prism — rectangular, triangular, hexagonal, you name it.

Cone

A cone is exactly one-third of a cylinder with the same base and height.

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

That $\tfrac{1}{3}$ is the only thing different from the cylinder formula — remember it as “ice-cream cones are a third as much as the cup they fit on.”

Example: cone with radius 3 and height 6 → $\tfrac{1}{3}\pi(9)(6) = 18\pi$.

Sphere

A sphere is just a ball.

$$V = \tfrac{4}{3}\pi r^3$$

Notice the $r^3$ — volume always involves three dimensions, so the radius is cubed.

Example: a basketball with radius 12 cm: $\tfrac{4}{3}\pi (12)^3 = \tfrac{4}{3}\pi(1728) = 2304\pi \approx 7238\,\text{cm}^3$.

Rectangular prism (box)

$V = l \cdot w \cdot h$. The simplest of them all — length times width times height.

Example: a moving box 24 in × 18 in × 18 in has volume $7776\,\text{in}^3$.

Pyramid

A pyramid is exactly one-third of a prism with the same base and height — just like a cone is a third of a cylinder.

$V = \tfrac{1}{3} \cdot B \cdot h$, where $B$ is the area of the base.

Memory tricks

• Cylinder = pizza × height.
• Cone = third of a cylinder.
• Pyramid = third of a prism.
• Sphere = $\tfrac{4}{3}\pi r^3$ → “four thirds pie cube” — say it three times and you’ll remember it forever.
• Prism = base area × height.

Common mistakes

• Using diameter instead of radius (radius is half the diameter).
• Forgetting to cube units (cm³, not cm).
• Skipping the $\tfrac{1}{3}$ on cones/pyramids or the $\tfrac{4}{3}$ on spheres.
• Plugging the slant height into the formula instead of the perpendicular height.
• Forgetting to convert units (don’t mix inches with feet without converting).

Composite solid example

A grain silo is a cylinder with a half-sphere on top. The cylinder has radius 4 m and height 10 m. Find the total volume.

• Cylinder: $\pi (4)^2 (10) = 160\pi$.
• Half-sphere: $\tfrac{1}{2} \cdot \tfrac{4}{3}\pi (4)^3 = \tfrac{128}{3}\pi$.
• Total: $160\pi + \tfrac{128}{3}\pi = \tfrac{480 + 128}{3}\pi = \tfrac{608}{3}\pi \approx 636.7\,\text{m}^3$.

Quick practice

1. A spherical scoop of ice cream has radius 2 cm. What’s its volume? Answer: $\tfrac{32}{3}\pi \approx 33.5\,\text{cm}^3$.
2. A cylinder has radius 5 and height 12. Find the volume. Answer: $300\pi$.
3. A cone has radius 4 and height 9. Find the volume. Answer: $48\pi$.
4. A rectangular fish tank is 24 in × 12 in × 16 in. Volume in cubic inches? Answer: 4608.
5. How many cones of radius 3 and height 6 fit in a cylinder of the same dimensions? Answer: 3.
6. A swimming pool 25 m long, 10 m wide, and 2 m deep. Volume? Answer: 500 m³.
7. A pyramid has a square base of side 10 and height 12. Volume? Answer: $\tfrac{1}{3}(100)(12) = 400$.
8. The diameter of a basketball is 24 cm. What is its volume in terms of $\pi$? Answer: radius = 12; $V = \tfrac{4}{3}\pi(1728) = 2304\pi$.

Surface area vs volume — don’t confuse them

A cylinder’s surface area is $2\pi r^2 + 2\pi r h$ (two circles plus a rectangle wrapped around). A cylinder’s volume is $\pi r^2 h$. Different formulas, different units.

If a question asks how much paint you need, that’s surface area. If it asks how much water fits, that’s volume.

How volume scales with size

If you double every dimension of a 3D shape, the volume multiplies by $2^3 = 8$. Triple every dimension, volume goes up by 27. This is one of the most-tested SAT/ACT geometry traps — sliding a question from “increase the radius” to “increase the volume.”

Example. If the radius of a sphere triples, by what factor does the volume grow? Answer: $3^3 = 27$.

Volume in everyday units

Volume comes in different units depending on what you’re measuring.

• Cubic centimeters (cm³) = milliliters (mL). 1 cm³ = 1 mL.
• Cubic meters (m³) for swimming pools and rooms.
• Cubic feet (ft³) for fridges and shipping crates.
• Liters (L) = 1000 cm³. Common for drinks and gasoline.
• Gallons for fuel in the US (1 gal ≈ 3.785 L).

Knowing these conversions saves time on word problems that switch units mid-question.

Word problem strategy

A reliable 4-step approach for any volume word problem:

1. Sketch the shape. Even a rough drawing prevents formula mix-ups.
2. Label the given information. Radius? Diameter? Height? Slant height?
3. Pick the formula. Match it to the shape.
4. Convert units if needed. Then compute. Always include the cubic unit in your final answer.

Common SAT/ACT volume traps

• Giving you the diameter when the formula wants the radius.
• Mixing inches and feet within the same problem.
• Asking for the volume of a half-shape (hemisphere, half-cylinder) — remember to divide by 2.
• Asking how many small objects fit inside a larger one — divide the volumes, but check that the small object can actually pack efficiently (this is a packing problem, not pure volume).

FAQ

What’s the formula for the volume of a cylinder?

$V = \pi r^2 h$.

Why is a cone’s volume one-third of a cylinder’s?

Because if you pour three cones of liquid into a matching cylinder, it fills exactly.

What’s the formula for the volume of a sphere?

$V = \tfrac{4}{3}\pi r^3$.

Do I need the diameter or the radius?

The formulas use the radius — half of the diameter.

Will volume formulas be given on the SAT?

Yes — the SAT prints a reference sheet at the start of the math section with all the volume formulas you need.

How is volume different from surface area?

Volume measures the inside (cubic units). Surface area measures the outside (square units).

What’s the difference between height and slant height?

Height is the perpendicular distance from base to apex. Slant height runs along the surface of the cone or pyramid. Volume formulas always use the perpendicular height.

Can volume ever be negative?

No. Volume measures a physical quantity (size), so it’s always positive.

What’s the volume of a hemisphere?

Half a sphere’s volume: $V = \tfrac{2}{3}\pi r^3$.

What’s the volume of a triangular prism?

Area of the triangular base times the length: $V = \tfrac{1}{2}(b \cdot h) \cdot \ell$.

Does the formula for a cylinder’s volume work for any cylinder, or only “right” cylinders?

A right cylinder (axis perpendicular to base) uses $V = \pi r^2 h$ where $h$ is the perpendicular height. For an oblique cylinder (tilted axis), the formula still works — just use the perpendicular height, not the slant length.

What about the volume of irregular shapes?

For anything not a clean prism, cylinder, cone, sphere, or pyramid, you use water displacement: drop the object into a graduated cylinder and measure how much the water level rises. The rise (in mL) equals the object’s volume (in cm³).

What is $\pi$, anyway?

$\pi$ is the ratio of a circle’s circumference to its diameter — about $3.14159$. It appears in every formula involving circles, spheres, cylinders, and cones because all of these are built on the geometry of a circle.

Is there a single formula that covers prisms, pyramids, cylinders, and cones?

Yes, in two families. Prisms and cylinders: $V = (\text{base area}) \times \text{height}$. Pyramids and cones: $V = \tfrac{1}{3} (\text{base area}) \times \text{height}$. That $\tfrac{1}{3}$ is the reason a cone is exactly one-third the volume of the cylinder it sits inside.

One last reminder

Progress in math compounds. A 1% improvement every day for 100 days yields nearly a 3x improvement overall, because each new concept builds on the last. The students who pull ahead aren’t the ones who study the longest — they’re the ones who study consistently, review their mistakes, and refuse to skip the foundations. Show up tomorrow. Then show up the day after. The results take care of themselves.

If you found something useful here, save this article and revisit it after your next practice session. You’ll catch nuances on the second read that you missed on the first, because by then you’ll have the experience to recognize them. Happy practicing.

For loads of practice, dive into our 7th- and 8th-grade math worksheets.