Concrete Calculator Cylinder: Volume in Yards & Bags

This concrete calculator for a cylinder works out the volume of concrete needed to fill a cylindrical column, footing, or pier. You enter the diameter (or radius) and the height of the cylinder, and the calculator returns the volume in cubic feet, cubic yards, and the number of 60-lb or 80-lb bags of premixed concrete required. It uses the standard formula for the volume of a cylinder: π × radius² × height.

Formula

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

V = π × r² × h

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

If you measure the diameter (d) instead of the radius, the formula becomes V = π × (d/2)² × h. To convert cubic feet to cubic yards, divide by 27 (since 1 yard = 3 feet, and 3³ = 27). For metric, 1 cubic meter = 1,000,000 cubic centimeters, and 1 cubic yard ≈ 0.7646 cubic meters.

Worked Example

Using the default values from the calculator: diameter = 1 ft, height = 4 ft.

1. Radius = diameter / 2 = 1 / 2 = 0.5 ft
2. Base area = π × (0.5)² = π × 0.25 ≈ 0.7854 sq ft
3. Volume = 0.7854 × 4 = 3.1416 cu ft
4. Volume in cubic yards = 3.1416 / 27 ≈ 0.1164 cu yd
5. For 60-lb bags: each bag yields about 0.45 cu ft of concrete. Bags needed = 3.1416 / 0.45 ≈ 6.98, so round up to 7 bags.
6. For 80-lb bags: each bag yields about 0.6 cu ft. Bags needed = 3.1416 / 0.6 ≈ 5.24, so round up to 6 bags.

The calculator shows 3.14 cu ft, 0.12 cu yd, 7 bags (60-lb), and 6 bags (80-lb). Always round up to the nearest whole bag because you cannot order a fraction of a bag, and it is better to have a little extra than to run short.

When to Use This Calculator

You need a cylinder concrete calculator for any round concrete element that is uniform in cross-section. Common uses include:

• Deck footings – round piers that support posts
• Fence posts – cylindrical holes filled with concrete
• Light pole bases – round pads or piers
• Structural columns – vertical cylindrical supports
• Caissons or drilled shafts – deep foundation elements

For a tapered cylinder (like a traffic barrier or a flared footing), this simple formula will overestimate or underestimate the volume. In that case, use the average radius or a more complex formula for a frustum (truncated cone).

How to Choose the Right Inputs

Accuracy starts with measurement. Here are the key points:

• Diameter vs. radius: If you measure the radius directly (center to edge), halve the diameter. If you measure the circumference, divide by Ï€ to get the diameter.
• Height: Measure the full depth of the hole or the full height of the column. For a footing that is below grade, measure from the bottom of the excavation to the top of the concrete, not the top of the soil.
• Units: Keep all measurements in the same unit. Mixing feet and inches is the most common error. Convert inches to feet by dividing by 12 (e.g., 6 inches = 0.5 ft).
• Over-excavation: If the hole is wider at the top than the bottom (which often happens when digging), measure the average diameter, not the widest point.

Common Mistakes and Misconceptions

• Using diameter instead of radius: Forgetting to divide the diameter by 2 quadruples the volume (since area scales with the square of the radius). A 1-ft diameter column is not the same as a 1-ft radius column.
• Unit mix-ups: Entering inches as feet or vice versa. Always convert to the same unit before calculating.
• Rounding too early: If you round the radius to 0.5 ft from 0.49 ft, the volume changes noticeably. Keep full precision until the final step.
• Assuming the hole is perfectly cylindrical: Hand-dug holes are rarely perfect. Add 5–10% extra concrete to account for irregularities and spillage.
• Bag yield confusion: A 60-lb bag yields about 0.45 cu ft, and an 80-lb bag yields about 0.6 cu ft. These are standard for Quikrete and similar mixes, but always check the bag label because some mixes have different yields.

Comparing Cylinder Volume to Other Shapes

If you are planning a project with both cylindrical and rectangular elements, you need to add the volumes. A rectangular footing uses V = length × width × height. For example, a 2 ft × 2 ft × 1 ft slab is 4 cu ft, while a 1-ft diameter, 4-ft tall cylinder is about 3.14 cu ft. The cylinder is more efficient for supporting a point load because it uses less concrete for the same depth. However, a square footing is easier to form and may be more stable on soft soil. For a project that mixes shapes, calculate each volume separately and sum them.

Cost and Ordering Considerations

Once you have the volume in cubic yards, you can estimate the cost of ready-mix concrete. As of 2024, the average price for a cubic yard of standard concrete is roughly $120–$150, but prices vary by region, season, and the type of mix. For small projects (less than 1 cubic yard), it is often cheaper to use bagged mix. A 60-lb bag costs about $4–$6, and an 80-lb bag about $5–$8. For a 1-ft diameter, 4-ft tall cylinder (0.12 cu yd), you would need about 7 bags of 60-lb mix, costing roughly $28–$42. For larger volumes, ready-mix is more economical, but you must order at least a minimum quantity (often 1–3 cubic yards) and pay for delivery. Always order 5–10% extra to account for waste, spillage, or uneven holes.

Safety and Practical Tips

• Wear gloves and eye protection when mixing concrete; the cement powder is caustic and can cause burns.
• Do not breathe the dust – use a dust mask when pouring dry mix.
• Use a wheelbarrow or mixer for large batches; mixing by hand is tiring and can lead to inconsistent results.
• For deep holes, use a concrete tube (sonotube) to keep the shape and prevent soil from collapsing into the concrete.
• Let the concrete cure properly – keep it moist for at least 3–7 days for maximum strength.

Frequently Asked Questions

How many 80-lb bags of concrete do I need for a 12-inch diameter tube that is 4 feet tall?
Using the formula: radius = 6 inches = 0.5 ft, height = 4 ft. Volume = π × (0.5)² × 4 ≈ 3.14 cu ft. Each 80-lb bag yields about 0.6 cu ft, so you need 3.14 / 0.6 ≈ 5.24, so round up to 6 bags.

What is the formula for the volume of a concrete cylinder in cubic yards?
First calculate the volume in cubic feet: V = π × r² × h (r and h in feet). Then divide by 27 to get cubic yards. For example, a 2-ft diameter, 3-ft tall cylinder: r = 1 ft, V = π × 1² × 3 ≈ 9.42 cu ft, and 9.42 / 27 ≈ 0.35 cu yd.

Can I use this calculator for a sonotube?
Yes. A sonotube is a cylindrical form, so the volume is exactly the same as any other cylinder. Measure the inside diameter of the tube (not the outside) and the height you plan to fill. If the tube is partially buried, measure the height of the concrete, not the height of the tube above ground.

Why does the calculator show a different number of bags than the ready-mix yardage?
Ready-mix concrete is sold by the cubic yard, while bagged concrete is sold by weight. The bag yield depends on the mix (e.g., 60-lb yields 0.45 cu ft, 80-lb yields 0.6 cu ft). The calculator uses those standard yields, but always check the bag label because some mixes (like high-strength or fiber-reinforced) have different yields.

What if my hole is not a perfect cylinder?
If the hole is wider at the top than the bottom (a tapered hole), the cylinder formula will overestimate the volume if you use the top diameter, or underestimate if you use the bottom diameter. Use the average diameter (top + bottom) / 2 for a better estimate. For a truly conical shape, use the formula for a frustum: V = (π × h / 3) × (R² + Rr + r²), where R is the top radius and r is the bottom radius.

How much concrete do I need for a 6-inch diameter post hole that is 3 feet deep?
Radius = 3 inches = 0.25 ft. Volume = π × (0.25)² × 3 ≈ 0.589 cu ft. That is about 0.022 cu yd. With 60-lb bags (0.45 cu ft each), you need 0.589 / 0.45 ≈ 1.31, so 2 bags. With 80-lb bags (0.6 cu ft each), you need 0.589 / 0.6 ≈ 0.98, so 1 bag.

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in d | Diameter | ft | 1 | 0
in h | Height | ft | 4 | 0
out volume_ft | Volume | cu ft | pi * (d/2)^2 * h | 2
out volume_yd | Volume | cu yd | (pi * (d/2)^2 * h) / 27 | 2
out bags60 | 60-lb bags | bags | ceil((pi * (d/2)^2 * h) * 0.45 / 0.6) | 0
out bags80 | 80-lb bags | bags | ceil((pi * (d/2)^2 * h) * 0.45 / 0.8) | 0