Concrete Cylinder, Column & Post Calculator: Round Piers
This concrete cylinder, column and post calculator uses diameter and height to find the volume of round pours like piers, sonotube columns and deck footings. It's built for circular shapes, so you get accurate yards and bag counts without guessing at the geometry of a cylinder.
Estimated concrete
Estimates only. Add ~5–10% for waste. Bag yields: 40 lb ≈ 0.30, 60 lb ≈ 0.45, 80 lb ≈ 0.60 cu ft. Concrete ≈ 150 lb per cu ft.
How the Concrete Cylinder, Column & Post Calculator works
- 1
Enter your dimensions
Type the length, width and thickness of your slab, footing or pad and choose your units, feet, inches or meters.
- 2
Get instant volume
See the result in cubic yards, cubic feet and cubic meters, plus weight, the moment you type, no page reloads.
- 3
Buy the right amount
We convert volume into the exact number of 40, 60 and 80 lb bags, truck loads and cost so you order without waste or shortfalls.
The formula
Cubic feet = pi x (Diameter_in / 2 / 12)^2 x Height_ft x Qty
- ·Diameter_in = tube or column diameter (inches)
- ·Height_ft = column or pier height (feet)
- ·Qty = number of identical columns
- ·pi = 3.14159
- ·/12 converts the radius from inches to feet
The radius in feet is the diameter divided by 2 then by 12. Squaring that radius, multiplying by pi and the height gives the volume of one column, which you then multiply by the quantity.
Worked examples
Example 1: One 10-inch sonotube, 4 ft tall
- Radius = 10 / 2 / 12 = 0.417 ft
- Radius squared = 0.1736
- Volume = 3.14159 x 0.1736 x 4 = 2.18 ft3
- Bags = 2.18 / 0.60 = 3.6, round up to 4
Result: About 2.18 ft3, or four 80 lb bags
Example 2: Three 12-inch piers, 3 ft tall each
- Radius = 12 / 2 / 12 = 0.5 ft
- Volume each = 3.14159 x 0.25 x 3 = 2.36 ft3
- Total = 2.36 x 3 = 7.07 ft3
- Yards = 7.07 / 27 = 0.26 yd3
Result: About 7.07 ft3 total, or 0.26 cubic yards
Concrete calculators by project type
Concrete bag yield & coverage
How much mixed concrete a standard bag yields, and how far a cubic yard goes at common slab depths.
| Bag size | Yield (cu ft) | Bags per cubic yard |
|---|---|---|
| 40 lb | 0.30 | 90 |
| 60 lb | 0.45 | 60 |
| 80 lb | 0.60 | 45 |
- 40 lb
- 60 lb
- 80 lb
Related guides
Concrete cylinder, column & post calculator FAQs
How do you calculate concrete for a round column?
Volume equals pi × radius² × height, where radius is half the diameter. For example, a 12-inch (1 ft) diameter column 8 ft tall is 3.1416 × 0.5² × 8 = 6.28 ft³, about 0.23 cubic yards.
How much concrete fills a 10-inch sonotube?
A 10-inch-diameter tube holds about 0.55 ft³ per foot of height, so a 4 ft tall pier needs roughly 2.2 ft³, or about 0.08 cubic yards. That's around four 80 lb bags per pier.
How many bags of concrete for a fence post hole?
A typical post hole 8 inches wide and 2 ft deep holds about 0.7 ft³, which is roughly one to two 80 lb bags after subtracting the post's volume. Wider or deeper holes for larger posts need proportionally more.
What diameter should a deck footing pier be?
Deck pier diameter depends on load and soil bearing, but 10 to 12 inches is common for residential footings. Larger tributary loads or weak soils call for a bigger diameter or a flared footing base.
Should I add extra concrete for a flared or belled base?
Yes, a bell or footing pad at the bottom of a pier holds significantly more than the straight tube above it. Estimate the base as a separate cylinder or slab and add it to the column volume.
Is bagged concrete enough for columns and posts?
Bagged mix is usually fine for individual posts and small piers, since each hole often needs only a few 80 lb bags. For many columns at once, ready-mix at about $125–$165 per yard can save time and money.
What is the formula for concrete in a round column?
Take the radius in feet (diameter in inches divided by 2, then by 12), square it, and multiply by pi and the height in feet. A 12-inch tube 5 ft tall is 3.14159 x 0.25 x 5 = 3.93 cubic feet. Multiply by the number of identical columns for the total.
How many 80 lb bags fill a 10-inch sonotube 4 feet tall?
That tube holds about 2.18 cubic feet, and each 80 lb bag yields roughly 0.60 cubic feet, so you need four bags. Buy an extra bag as insurance, since tubes often take slightly more than the theoretical volume. A 12-inch tube of the same height needs about six bags.
How do I calculate concrete for several piers at once?
Find the volume of one pier, then multiply by the number of piers. Six 10-inch piers at 3 ft tall are 1.64 ft3 each, or 9.82 ft3 total, which is about 0.36 cubic yards. Ordering all piers together often justifies ready-mix over bags.
How much larger should a post hole be than the post?
A common guideline is a hole diameter about three times the post width, so a 4-inch post gets a 12-inch hole. The extra annular space, minus the post volume, is what fills with concrete. The fence-post mode subtracts the post to give the true concrete needed.
Does a belled or flared footing base need extra concrete?
Yes, a bell or flare at the bottom adds volume beyond the straight cylinder, so add roughly 15 to 25% depending on how wide the bell is. The plain cylinder formula underestimates a belled pier. Order extra rather than come up short on a footing.
How deep should a deck footing pier go?
Deck piers should reach below the frost line and bear on undisturbed or compacted soil, often 36 to 48 inches deep in cold climates. Enter the full pier height, including the portion above grade, into the calculator. Local code sets the minimum depth and required diameter.
Can I mix bags by hand for columns and posts?
Hand-mixing is practical for a handful of posts or piers, but it gets tiring past roughly ten 80 lb bags. For fence posts, many people use fast-setting mix poured dry into the hole and then wetted. For multiple structural piers, a mechanical mixer or ready-mix saves time and gives more consistent strength.