capsule volume calculator
Calculate a capsule (cylinder with rounded ends) volume in cubic feet, cubic yards, gallons, and liters — for horizontal tanks and vessels.
A capsule shape — a cylinder with a rounded dome on each end — is how most horizontal pressure tanks and propane cylinders are built. Enter the diameter and the straight (cylindrical) length to get volume in cubic feet, cubic yards, gallons, and liters.
How this calculator works
Capsule volume is a cylinder’s volume for the straight section, plus a full sphere’s volume for the two rounded ends combined.
Formula: Cubic feet = [π × (diameter ÷ 2)² × straight length] + [(4/3) × π × (diameter ÷ 2)³]. Cubic yards = ft³ ÷ 27. Gallons = ft³ × 7.48052. Liters = ft³ × 28.3168.
Worked example
A capsule with a 2 ft diameter and 6 ft straight length:
- Radius: 2 ÷ 2 = 1 ft
- Cylinder portion: π × 1² × 6 ≈ 18.85 ft³
- Sphere portion (both ends): (4/3) × π × 1³ ≈ 4.19 ft³
- Total: 18.85 + 4.19 ≈ 23.04 ft³
- Cubic yards: 23.04 ÷ 27 ≈ 0.853 yd³
- Gallons: 23.04 × 7.48052 ≈ 172.3 gal
- Liters: 23.04 × 28.3168 ≈ 652.4 L
Reference
| Diameter × Straight length (ft) | Cubic feet |
|---|---|
| 1 × 4 | 3.67 ft³ |
| 2 × 6 | 23.04 ft³ |
| 3 × 8 | 70.69 ft³ |
How to measure
Measure diameter across the widest point of the tank, and the straight length of just the cylindrical middle section, not counting the two domed ends. This applies to horizontal propane tanks, pressure vessels, and dome-ended septic or water tanks. For a plain flat-ended cylinder instead, use the Cylinder Volume Calculator.
Frequently asked questions
What shape is a capsule in this calculator?
A straight cylindrical section with a dome (half-sphere) capping each end — like a pill, a propane cylinder, or many horizontal pressure vessels and septic tanks.
What's the formula for capsule volume?
It's a cylinder's volume plus a full sphere's volume: V = π × r² × straight length, plus (4/3) × π × r³. The two rounded ends together make exactly one full sphere.
What is 'straight length' in the input?
It's the length of the cylindrical middle section only — not including the two rounded end caps. If you measured the tank's total end-to-end length, subtract the diameter (roughly the length the two domed ends add together) to get the straight section.
Where does this shape actually show up?
Horizontal propane and fuel tanks, many pressure vessels, and some horizontal septic or water tanks use this rounded-end shape rather than flat ends, since domed ends handle internal pressure better.
How does a capsule's volume compare to a plain cylinder of the same length?
A capsule holds more, since the two rounded ends add extra volume beyond a flat-ended cylinder of the same straight length. For a quick estimate ignoring the ends, use the Cylinder Volume Calculator.
Why does the diameter affect volume so much through the sphere portion?
The end-cap volume depends on radius cubed, so a wider tank adds disproportionately more volume through its rounded ends than a narrow one, even at the same straight length.
Estimates only. Verify quantities with your supplier before purchasing.