Concrete Calculator Cylinder Yards: How to Find Volume

This calculator works out the volume of a concrete cylinder in cubic yards. You enter the cylinder’s diameter (or radius) and its height or length, and it returns the volume in cubic yards, along with the volume in cubic feet and cubic meters for convenience. The calculation uses the standard formula for the volume of a cylinder: Ï€ × radius² × height.

Formula

The volume of a cylinder is the area of its circular base multiplied by its height. The formula is:

V = π × r² × h

Where:

• V = volume (cubic feet, cubic yards, or cubic meters)
• Ï€ (pi) ≈ 3.14159
• r = radius of the cylinder (half the diameter), in the same unit as h
• h = height or length of the cylinder, in the same unit as r

Since concrete is usually ordered by the cubic yard in the US, you divide the volume in cubic feet by 27 (because 1 cubic yard = 27 cubic feet). If you measure in meters, the volume is directly in cubic meters (1 m³ = 1.308 yd³).

Worked Example

Using the default values from the calculator above: a cylinder with a diameter of 2 feet and a height of 4 feet.

1. Find the radius: r = d / 2 = 2 / 2 = 1 ft
2. Calculate the base area: π × r² = 3.14159 × 1² = 3.14159 ft²
3. Multiply by height: 3.14159 × 4 = 12.566 ft³
4. Convert to cubic yards: 12.566 / 27 = 0.4654 yd³

The calculator rounds to two decimals, so it shows 0.47 cubic yards. The same volume in cubic feet is 12.57 ft³, and in cubic meters it is 12.566 × 0.0283168 = 0.356 m³.

When to Use a Cylinder Volume for Concrete

Cylindrical concrete elements are common in construction and DIY projects. You need this calculation when pouring:

• Footings for decks, posts, or light poles – typically round holes dug into the ground.
• Pier foundations – cylindrical supports that transfer loads to the soil.
• Concrete columns – vertical structural members.
• Caissons or drilled shafts – deep foundation elements.
• Sonotube forms – cardboard tubes used to shape concrete columns above or below grade.

For any of these, you need the volume to order the right amount of ready-mix concrete. Ordering too little means a delay while you order more; ordering too much wastes money.

How to Read the Result

The first output is the volume in cubic yards, which is the standard unit for ordering concrete in the US and Canada. A typical ready-mix truck carries about 10 cubic yards, so a result of 0.47 yd³ means you would need a fraction of a truck – often you will pay a short-load fee if you order less than a full truck. For small volumes, consider mixing bags yourself: a 60-lb bag yields about 0.45 ft³, and an 80-lb bag yields about 0.6 ft³. So 12.57 ft³ would require about 28 60-lb bags or 21 80-lb bags.

The cubic feet and cubic meter outputs help when you are comparing with bag labels or working in metric. Always double-check your measurements before ordering – a small error in diameter makes a big difference because the radius is squared.

Common Mistakes and How to Avoid Them

Several errors are frequent when calculating concrete for cylinders:

• Using diameter instead of radius – the formula requires the radius. If you enter the diameter directly, you get four times the actual volume. Always halve the diameter first.
• Mixing units – if you measure diameter in inches and height in feet, the result is meaningless. Convert everything to the same unit first. For example, 12 inches = 1 foot, so a 12-inch diameter is 1 foot.
• Forgetting the 27 conversion – cubic feet to cubic yards is not dividing by 3; it is dividing by 27 (3³). A common mistake is to divide by 3, which gives a volume three times too small.
• Not accounting for the actual hole size – when digging a footing, the hole is often larger than the post or tube. Measure the hole, not the post. Also, if you use a tube form, the tube’s inside diameter is what matters, not the outside.
• Ignoring waste and over-excavation – it is standard practice to add 5–10% extra for spillage, uneven ground, or slight over-digging. For a 0.47 yd³ pour, adding 10% means ordering 0.52 yd³.

Limitations of the Formula

The formula assumes a perfect cylinder with a constant cross-section. Real-world pours often deviate:

• Irregular holes – hand-dug holes are rarely perfectly round or straight-sided. If the hole is wider at the top than the bottom, the volume is larger than a perfect cylinder. In such cases, measure the average diameter or use a cone frustum formula instead.
• Sloped bottoms – if the bottom of the hole is not flat, the volume changes. A common practice is to level the bottom with gravel or sand before pouring.
• Reinforcement – rebar or a post inside the cylinder displaces a small amount of concrete. For most footings, this displacement is negligible (less than 1–2%), but for large columns with heavy rebar, you could subtract the volume of the steel.
• Moisture and shrinkage – wet concrete shrinks slightly as it cures, but the ordered volume is based on the wet volume. You do not need to adjust for shrinkage in the order.

Comparing Cylinders to Other Shapes

Cylinders are not the only shape you might pour. Here is how they compare to common alternatives:

• Rectangular slab – volume = length × width × thickness. For a 10 ft × 10 ft slab 4 inches thick (0.333 ft), volume = 10 × 10 × 0.333 = 33.3 ft³ = 1.23 yd³.
• Square footing – volume = side × side × depth. A 2 ft × 2 ft × 1 ft footing is 4 ft³ = 0.148 yd³.
• Cone frustum (trapezoidal footing) – volume = (Ï€ × h / 3) × (R² + Rr + r²), where R is the bottom radius and r is the top radius. This is more accurate for flared footings.

For a given height and footprint, a cylinder contains more concrete than a square footing with the same width because the circle fits inside the square. That means a round footing is often more efficient for supporting a post.

Safety and Practical Tips

Concrete work involves heavy materials and chemical burns. Keep these points in mind:

• Wear protective gear – gloves, long sleeves, and eye protection. Wet concrete is highly alkaline and can cause skin burns.
• Check the hole depth – for frost protection, footings must extend below the frost line in your area. The calculator gives volume, not depth; you must verify local building codes for minimum footing depth.
• Use a tube form for above-grade columns – Sonotube or similar forms hold the wet concrete in place and give a smooth finish. They come in standard diameters (6, 8, 10, 12, 16, 18, 24, 30, 36 inches).
• Order a little extra – as mentioned, add 5–10% to the calculated volume to cover waste. It is cheaper to have a few bags left over than to run short.
• Know your truck capacity – if you order ready-mix, the driver will not pour more than the truck holds. For volumes under 1 yd³, bagged concrete is usually more practical.

Frequently Asked Questions

How many 80 lb bags of concrete do I need for a 12-inch diameter cylinder that is 3 feet tall?

First, calculate the volume: radius = 6 inches = 0.5 ft, height = 3 ft. Volume = π × 0.5² × 3 = 2.356 ft³. An 80-lb bag yields about 0.6 ft³, so you need 2.356 / 0.6 = 3.93 bags. Round up to 4 bags. If you want to include 10% waste, buy 5 bags.

What is the formula for cubic yards of a cylinder?

The formula is V = π × r² × h, where r is the radius and h is the height, both in feet. Then divide the result by 27 to get cubic yards. If you measure in inches, convert to feet first by dividing by 12. If you measure in meters, the result is in cubic meters, and you can multiply by 1.308 to get cubic yards.

How much concrete do I need for a 4×4 post hole?

It depends on the hole diameter and depth. For a typical 8-inch diameter hole that is 3 feet deep, the volume is π × (4/12)² × 3 = 1.047 ft³ = 0.039 yd³. That is about 1.75 80-lb bags. For a 12-inch hole, the volume is π × (6/12)² × 3 = 2.356 ft³ = 0.087 yd³, or about 4 bags.

Does the calculator account for the post inside the hole?

No, it assumes a solid cylinder of concrete. If you are setting a post in the hole, the post displaces some concrete. For a 4×4 post (actual 3.5 in × 3.5 in) in an 8-inch hole, the post occupies about 0.26 ft³ per foot of depth, which is roughly 10% of the hole volume. You can subtract that if you want a precise order, but most contractors ignore it and order the full volume.

Should I order ready-mix or use bags for a small cylinder?

For volumes under 1 cubic yard, bags are usually more practical. Ready-mix companies often have a minimum order (typically 1–3 yards) and charge short-load fees. For a 0.47 yd³ pour, you would need about 21 80-lb bags, which is manageable for a DIY project. For larger volumes, ready-mix is faster and often cheaper per yard.

What happens if I order too little concrete?

If you run short, you have to stop the pour, wait for a new delivery, and hope the first batch does not set. That creates a cold joint – a weak seam where the new concrete meets the old. To avoid this, always order 5–10% more than the calculated volume. It is much easier to dispose of a little extra than to fix a structural problem.

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in d | Diameter | ft | 2 | 0
in h | Height / Length | ft | 4 | 0
out cy | Volume (cubic yards) | yd³ | (pi * (d / 2)^2 * h) / 27 | 2
out cf | Volume (cubic feet) | ft³ | pi * (d / 2)^2 * h | 2
out cm | Volume (cubic meters) | m³ | (pi * (d / 2)^2 * h) * 0.0283168 | 2