EstimatorKitFree cylinder volume calculator
Cylinder volume, solid, hollow or part full
Enter what you measured across a round section — the diameter, the radius, or a tape run around the outside — and this returns πr²h in cubic feet, cubic inches, cubic yards, cubic meters, US gallons and liters. It also covers the two cases most volume tools drop: a hollow section, where the ring of wall and the empty bore are reported separately, and an upright cylinder standing part full. A piece count multiplies before anything is rounded, so a run of six identical piers is answered as one order rather than six.
- 100% free
- No signup
- 3 cases
- Diameter, radius or girth
- 6 output units
A column form, a post hole, a fence-post backfill, a round planter, a log.
Straight across the widest point, inside face to inside face if it is a container.
The inside diameters a building-supply yard stocks cardboard column forms in. A form is sized by its bore, so the tube is the finished pier.
A unit written in a box always wins over the one in its label, so 300 mm against a field marked inches is read as 300 mm.
Volume of 6 cylinders
18.8 cu ft
- Each piece
- 3.14 cu ft
- Cubic inches
- 32,572
- Cubic yards
- 0.7
- Cubic meters
- 0.53
- US gallons
- 141
- Liters
- 534
The working
- Diameter 12 in, radius 6 in
- Full circle 113 sq in = 0.79 sq ft
- Times 4 ft along the axis, times 6 pieces
Filled with concrete, that is
- 80 lb bags at 0.6 cu ft each
- 32
- 60 lb bags at 0.45 cu ft each
- 42
- 40 lb bags at 0.3 cu ft each
- 63
Yields are the ones printed on the bag: yield printed on an 80 lb bag of pre-mixed concrete. Counts go up to the whole bag, and no allowance for spillage is added here.
How to calculate the volume of a cylinder
Three decisions, and the first two are about what you are looking at rather than about arithmetic.
Say which of the three round things you have
Solid all through is a pier, a post-hole backfill, a log or a round planter. Hollow is a pipe, a sleeve or a liner, where the material you are buying is the ring of wall and the bore is empty. Part full is an upright drum or butt with something standing in the bottom of it. Picking wrong is not a rounding error: read a 6 in pipe with a half-inch wall as solid and you have overstated the material in it by a factor of three.
Measure across the section — or around it, which is usually easier
Diameter is straight across the widest point, radius is half of that, and circumference is a flexible tape wrapped round the outside. The last one is there because a form tube already dropped into a hole will not let a rigid rule across its mouth, and a tape round it takes two seconds. Whatever you pick applies to both the outside and the bore, so a pipe measured by girth stays measured by girth.
Set how many identical pieces, then read the volume
Deck footings, fence posts and bollards come in sets, so the count multiplies before anything is rounded — which matters, because six piers pooled into one order take 32 bags of concrete where rounding each pier separately takes 36. Cubic feet leads, with cubic inches, yards, meters, gallons and liters beside it, and the Copy button hands over the dimensions and every unit as plain text.
Technical specifications
| Cases | Solid all through, hollow wall, and part-filled standing upright |
|---|---|
| Section taken as | Diameter, radius, or a circumference divided by 3.141592653589793 |
| Batch size | 1 to 999 identical pieces, pooled before any rounding happens |
| Form tube presets | 6, 8, 10, 12, 14, 16 and 18 in inside diameter, set with a single button |
| Hollow output | Ring of wall and bore capacity separately, plus gallons per foot of run |
| Part-fill output | Contents, percent of the way up, and the gallons still to go |
| Concrete equivalents | 80 lb at 0.6 ft³, 60 lb at 0.45 ft³, 40 lb at 0.3 ft³ — bag-printed yields |
| Stored or sent | Nothing; the measurements live in the tab and go when it closes |
Frequently asked questions
How much concrete does a 12 inch form tube take per foot of depth?
0.785 cubic feet for every foot of depth. A 12 in tube is a circle 6 in in radius, so its section is π × 0.5² = 0.7854 ft², and depth just multiplies it. A 4 ft pier is therefore 3.14 ft³, which is six 80 lb bags at the 0.6 ft³ each of them yields — the sixth bag existing only because the fifth runs 0.24 ft³ short.
How do I get the volume of the metal in a pipe rather than what the pipe carries?
Subtract the bore from the outside: π × (outer radius² − inner radius²) × length. The hollow setting does exactly that and reports both halves, because they answer different questions — the ring is what a supplier weighs and prices, the bore is what the run holds. If your spec gives a wall thickness rather than an inside diameter, double the thickness and take it off the outside diameter first: a 6 in pipe with a 1/2 in wall has a 5 in bore.
What happens if I type a diameter into a field that wants a radius?
The answer comes out four times too big, and nothing on screen looks wrong. Area goes with the square of the radius, so doubling the input quadruples the result — which is why this page lets you say which one you measured instead of assuming. The same trap runs the other way: a radius entered as a diameter reports a quarter of the true volume, and a quarter of a concrete order is a very visible shortfall on pour day.
Is a 55 gallon drum actually 55 gallons?
Filled to the brim it is closer to 57.7. A standard steel drum measures about 22.5 in across the inside and stands about 33.5 in tall, which works out at 7.71 ft³ or 57.7 US gallons. The 55 on the label is a fill rating with headspace left for expansion and for the closing ring, not a measurement of the shell.
Does the volume change if the cylinder is lying on its side?
No — πr²h does not care about orientation, and a tube holds the same amount whichever way it is set down. What changes is the relationship between a depth reading and the contents: upright, half the height is half the contents; on its side, half the diameter is still half but a quarter of the diameter is only 19.6% of the contents. That is a circular segment rather than a cylinder, and the tank page solves it.
Why does the tool ask how many pieces instead of letting me multiply?
Because whole bags are bought once, not once per hole. Six 12 in piers 4 ft deep need 18.85 ft³ between them, which is 32 eighty-pound bags; working out one pier at 5.24 bags, rounding it to six and multiplying gives 36. Four bags is not a rounding artifact, it is 320 lb of concrete carried home for nothing — or, if the count had gone the other way, a second trip.
About round sections and the two cases that get dropped
The formula is one line and has been for two thousand years: the area of the end times the distance between the ends. Every difficulty sits upstream of it, in the section. A radius has to be squared, so any error in it is squared too — measure a 12 in tube as 13 and you are 17% out before the depth is even applied, which costs most of a bag on one 4 ft pier and eight bags across nine of them. And the measurement itself is often the awkward part rather than the sum: a cardboard form already braced in a hole, a standpipe, a tree trunk and a silo all refuse a rule across the face while accepting a tape around the outside, which is why girth is an input here and not a conversion you are left to do first. A circumference divided by 3.1416 is exact, not an approximation.
The hollow case is the one that separates a real tool from a formula with a form around it. A pipe, a sleeve, a chimney liner and a cored column are all annuli, and the two numbers they produce are bought by different people: the ring of material is what a supply house weighs and prices, and the bore is what the run will carry. Gallons per foot of bore is the figure a flushing or purging schedule works from — a 1 in inside diameter holds 0.0408 gallons for every foot of its length, so a 300 ft run is a little over twelve gallons of standing content that has to go somewhere before anyone opens it. Generic volume pages answer neither question, because they take one diameter and stop.
Where this page stops is worth being clear about. It is geometry: it will happily size nine piers, and it will convert them into 40, 60 and 80 lb bags because that is what the cubic foot buys, but the full pour — footings, a slab, steps and the point where bags lose to a truck — belongs on the concrete calculator. A cylinder resting on its side with liquid in it is not this problem at all, because depth and contents stop being proportional; that is a circular segment and it is solved on the tank volume calculator. For boxes, cones, spheres and wedges, and for the conversion table between every cubic unit, the cubic feet calculator carries the other four solids.
What happens to the measurements you type
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — measurements, quantities, the prices your supplier quoted you — is uploaded, logged or kept, which is also why the calculators carry on working on a site with no signal.
The form-size buttons only rewrite the diameter box in front of you. Which one you tapped, how many piers you were pricing and how many times you retyped the girth are facts this page never learns.