Concrete Cylinder Calculator
Enter the diameter and height of your concrete cylinder to get the volume, weight, lateral surface area, total surface area, and the number of 60 lb or 80 lb concrete bags required. Works for columns, round piers, fence posts, and standard ASTM test cylinders. Switch between metric (cm) and imperial (inches) units at any time.
What does this calculator compute?
A concrete cylinder has a circular cross-section with a constant diameter from top to bottom. This calculator uses the cylinder volume formula V = pi x r^2 x h (where r is the radius and h is the height) to find the net concrete volume, then applies a user-defined waste factor and converts to cubic feet, cubic yards, weight in kilograms and pounds, and the number of standard pre-mix bags required. You can also choose the hollow mode to subtract an inner void, which is useful for concrete poured around a pipe or sleeve.
Concrete cylinder formula
Volume = pi x (D / 2)^2 x H, where D is the outer diameter and H is the height, both in the same unit. The radius is half the diameter. For a hollow cylinder, subtract the inner void: Volume = pi x H x (R_outer^2 - R_inner^2). Surface areas are: base area = pi x r^2 (one circular face), lateral area = 2 x pi x r x h (the curved side), and total surface area = 2 x base area + lateral area. Weight follows from volume multiplied by the concrete density, typically 2300-2400 kg/m3 for normal-weight concrete.
How many bags of concrete do you need?
A standard 80 lb bag of pre-mix concrete yields approximately 0.60 cubic feet of mixed material. A 60 lb bag yields about 0.45 cubic feet. Divide your required volume (including your waste allowance) by the per-bag yield and round up to the next whole bag. For volumes above about 1 cubic yard (27 cubic feet), ordering ready-mix concrete delivered by truck is typically more cost-effective and saves considerable labor.
Waste factor and ordering advice
A 10% waste factor is a common allowance for residential projects. It covers spilled mix, slightly uneven formwork dimensions, and leftover concrete that cannot be re-used. For perfectly formed cylindrical tubes (Sonotube style), 5% is often sufficient. Always round your bag count up, never down, to avoid running short mid-pour. If you are mixing a large number of cylinders, consider renting a drum mixer, which produces more consistent concrete than hand-mixing bags individually.
ASTM standard test cylinders
In concrete quality control, cylinders are cast from fresh concrete on-site, cured under controlled conditions, and then crushed in a lab to measure compressive strength. The most common size used in the United States is 6 in (150 mm) diameter by 12 in (300 mm) height, governed by ASTM C31 (practice for making and curing cylinders) and ASTM C39 (test method for compressive strength). A smaller 4 in x 8 in (100 mm x 200 mm) cylinder is also accepted and is increasingly preferred because it requires less material and is easier to handle.
Standard concrete cylinder sizes and uses
| Application | Diameter | Typical height | Standard |
|---|---|---|---|
| ASTM compressive strength test | 4 in (10 cm) | 8 in (20 cm) | ASTM C39 |
| ASTM compressive strength test (standard) | 6 in (15 cm) | 12 in (30 cm) | ASTM C39 |
| Fence / deck post footing | 10-12 in | 24-48 in | Varies by code |
| Residential column / pier | 12-16 in | 48-120 in | ACI 318 |
| Heavy structural column | 18-36 in | 10-40 ft | ACI 318 |
| Ready-mix truck drum | ~96 in | ~120 in | Industry standard |
Common pre-cast and cast-in-place cylinder dimensions used in construction and testing.
Frequently asked questions
How do I calculate the volume of a concrete cylinder?
Use the formula V = pi x r^2 x h, where r is the radius (half the diameter) and h is the height. Convert all measurements to the same unit first. For example, a 12 in diameter cylinder that is 48 in tall has a radius of 6 in, so V = 3.14159 x 6^2 x 48 = approximately 5,428.7 cubic inches, which equals about 3.14 cubic feet or 0.089 m3.
How many bags of concrete do I need for a 12 inch x 48 inch cylinder?
A 12 in diameter cylinder 48 in tall has a volume of about 3.14 ft3. With a 10% waste factor, you need roughly 3.46 ft3. At 0.60 ft3 per 80 lb bag, that is about 6 bags. Using 60 lb bags (0.45 ft3 each), you would need 8 bags. This calculator works out the exact count automatically once you enter your dimensions and bag size.
What is the standard size for a concrete test cylinder?
The most common size in the United States is 6 in (150 mm) in diameter and 12 in (300 mm) in height, specified by ASTM C31 and C39. The diameter-to-height ratio is always 1:2. A smaller 4 in x 8 in (100 mm x 200 mm) cylinder is also accepted and is growing in use because it requires less concrete and is easier to handle in the lab.
What density should I use for concrete?
Normal-weight concrete typically has a density of 2300-2400 kg/m3 (about 143-150 lb/ft3). Lightweight concrete mixes range from 1400-1800 kg/m3. Heavyweight concrete (used for radiation shielding) can exceed 3200 kg/m3. The default in this calculator is 2400 kg/m3, which is a safe mid-range value for standard ready-mix concrete.
Does the hollow cylinder option account for both inner and outer surfaces?
Yes. When you enable the hollow mode and enter an inner diameter, the calculator subtracts the inner void from the volume, adds the inner lateral surface to the surface area calculation, and treats each base as a ring (annulus) with area equal to pi x (R_outer^2 - R_inner^2). This is accurate for concrete columns poured around a steel pipe or sleeve.
When should I order ready-mix concrete instead of using bags?
Ready-mix concrete is generally more economical once you exceed about 1 cubic yard (27 cubic feet). Most ready-mix trucks have a minimum order of 1 yd3 and charge a short-load fee below that. For smaller volumes such as a few fence post footings, bagged pre-mix is more practical. Use the volume and bag outputs in this calculator to compare options for your specific project.