Free Volume Calculator: Find Cubic Feet, Gallons & Liters

Volume Calculator

Geometry

Volume Calculator

Shape

Unit

Length

Width

Height

Please enter valid, positive numbers for the selected shape's dimensions.

Volume

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Cubic Feet

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Cubic Meters

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Gallons (US)

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Liters

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Disclaimer: This calculator provides mathematical volume estimates based on the shape and measurements you enter. It does not account for material thickness, irregular real-world shapes, or fill/void factors (e.g., for soil, gravel, or concrete). Confirm critical measurements before ordering materials.

Volume Calculator: Formulas and Conversions for Every Shape

Quick answer: A volume calculator finds the three-dimensional space occupied by an object — a cube, cylinder, sphere, cone, or irregular container — by applying the correct geometric formula to its measured dimensions, then converts the result between units like liters, gallons, cubic feet, or cubic meters. This guide covers the formula for every common shape, worked examples, and the unit-conversion mistakes that most often throw off DIY measurements for things like soil, concrete, and aquariums.

Whether you’re figuring out how much concrete to order, how much water a fish tank holds, or how many cubic yards of mulch a garden bed needs, the question always comes down to the same thing: volume. A volume calculator takes the guesswork out of that math by applying the right geometric formula for the shape you’re measuring, and handling the unit conversion between metric and imperial systems automatically. Below are the formulas for every shape people search for most, plus fully worked, real-world examples.

Core Volume Formulas by Shape

Shape	Formula	Variables
Cube	V = s³	s = side length
Rectangular prism (box)	V = l × w × h	l = length, w = width, h = height
Cylinder	V = π × r² × h	r = radius, h = height
Sphere	V = (4/3) × π × r³	r = radius
Cone	V = (1/3) × π × r² × h	r = radius, h = height
Triangular prism	V = (1/2 × b × h) × l	b = base, h = triangle height, l = prism length

These formulas are the standard geometric equations for volume used across engineering, construction, and general math references, and every dedicated volume calculator is fundamentally just applying one of these based on the shape you select.

Worked Example #1: Rectangular Prism (Ordering Concrete)

You’re pouring a concrete slab 12 feet long, 10 feet wide, and 0.5 feet thick (6 inches).

V = l × w × h = 12 × 10 × 0.5 = 60 cubic feet

Since concrete is typically ordered in cubic yards, and 1 cubic yard = 27 cubic feet:

60 ÷ 27 ≈ 2.22 cubic yards

Most contractors round up and add a 5–10% buffer for spillage and uneven subgrade, bringing the practical order to roughly 2.4–2.5 cubic yards.

Worked Example #2: Cylinder (Fish Tank or Water Tank)

You have a cylindrical water tank with a 2-foot radius and a height of 5 feet.

V = π × r² × h = 3.1416 × 2² × 5 = 3.1416 × 4 × 5 = 62.83 cubic feet

Converting to gallons (1 cubic foot ≈ 7.48 gallons):

62.83 × 7.48 ≈ 470 gallons

Worked Example #3: Sphere (Storage Ball or Spherical Tank)

A spherical propane tank has a radius of 3 feet.

V = (4/3) × π × r³ = 1.333 × 3.1416 × 27 = 113.1 cubic feet

Converting to gallons: 113.1 × 7.48 ≈ 846 gallons

Worked Example #4: Cone (Pile of Material)

A conical pile of gravel measures 4 feet in radius and 6 feet tall.

V = (1/3) × π × r² × h = 0.333 × 3.1416 × 16 × 6 = 100.5 cubic feet

Converting to cubic yards: 100.5 ÷ 27 ≈ 3.7 cubic yards of gravel.

Common Unit Conversions for Volume

From	To	Multiply By
Cubic feet	Cubic yards	0.037
Cubic feet	Gallons (US)	7.48
Cubic meters	Liters	1,000
Cubic inches	Cubic feet	0.000579
Liters	Gallons (US)	0.264
Cubic meters	Cubic feet	35.31

Step-by-Step: How to Use a Volume Calculator

Select the shape you’re measuring — box, cylinder, sphere, cone, or another supported shape.
Enter the required dimensions (length/width/height, or radius/height, depending on the shape).
Choose your input unit (feet, inches, meters, centimeters).
Choose your desired output unit (cubic feet, gallons, liters, cubic yards, etc.).
Review the result, and if you’re ordering material like soil, concrete, or mulch, add a small buffer (5–10%) for waste and uneven surfaces, which is standard practice among contractors.

Common Mistakes People Make

Mixing units within the same calculation — measuring length in feet and height in inches without converting first.
Using diameter instead of radius in the cylinder, sphere, or cone formulas, which produces a volume that’s 4x too large.
Forgetting to convert cubic feet to cubic yards when ordering bulk materials like concrete, soil, or mulch, which are almost always sold by the yard.
Not accounting for irregular shapes — a garden bed or pond that isn’t a perfect rectangle needs to be broken into simpler shapes and summed, or estimated with an average depth.
Ignoring settling and waste when ordering loose materials, leading to running short mid-project.

Frequently Asked Questions

How do I calculate the volume of an irregular shape?

Break the irregular shape into simpler geometric shapes (rectangles, triangles, cylinders), calculate each one’s volume separately, and add them together, or use a displacement method (submerging the object in water and measuring the volume increase) for small solid objects.

How many cubic feet are in a cubic yard?

There are 27 cubic feet in one cubic yard, since a yard is 3 feet on each side and 3 × 3 × 3 = 27.

What’s the difference between volume and capacity?

Volume typically refers to the physical space an object occupies, while capacity usually refers to how much a container can hold, though in most practical calculators the two terms are used interchangeably and calculated the same way.

How do I convert liters to gallons?

Multiply the number of liters by 0.264 to get US gallons, or divide by 3.785 to get the same result.

Why does my calculated volume differ from the manufacturer’s stated capacity?

Manufacturer-stated capacity often accounts for wall thickness, headspace, or rounded product dimensions, while a geometric volume calculation assumes exact, idealized measurements.

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Conclusion

Every volume question, whether it’s a fish tank, a concrete slab, or a pile of gravel, comes down to matching the object’s shape to the right geometric formula and keeping your units consistent from start to finish. A volume calculator automates that process and handles the metric-to-imperial conversion for you, but understanding the underlying formulas — as shown in the worked examples above — helps you sanity-check the result and avoid the radius-versus-diameter mix-up that trips up so many DIY calculations.