Enter diameter and length — units can differ for each field
Tip: You only need two of three length inputs. Enter "Total Length" and "Diameter" and we'll compute the cylinder length automatically (Total − Diameter). Or enter "Cylinder Length" directly.
How to Use the Capsule Tank Volume Calculator
This calculator handles horizontal and vertical capsule tanks — any cylinder with two hemispherical domed ends. Follow these steps:
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Measure the Diameter The inside diameter of the cylindrical section — the outside diameter includes the walls and overstates the volume, so use it only for a rough figure. Use the unit dropdown to switch between feet, inches, centimetres, metres, or millimetres.
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Enter the Cylinder Length or Total Length The cylinder (body) length is the straight section only — the length of the tank minus both hemispherical caps. If you only know the full end-to-end length, enter it in the "Total Length" field instead. The calculator will subtract the diameter to derive cylinder length automatically.
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Set the Fill Level (optional) Use the slider to get the volume at a partial fill — useful for tank monitoring or delivery planning. The percentage is of the total volume, not of the depth; for a tank lying on its side, the note under the results shows how much it holds at a quarter, half and three-quarters of its depth. The default is 100% (full tank).
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Hit Calculate Results appear instantly in litres, US gallons, UK/Imperial gallons, cubic metres, cubic feet, cubic inches, and water weight in both kg and lbs. Use the Copy or Print buttons to save your results.
Capsule Tank Volume Formula Explained
A capsule is a cylinder with two hemispherical ends. The two hemispheres combined form exactly one complete sphere, so the total volume is:
where:
r = radius = Diameter ÷ 2
Lcyl = cylinder (body) length (not total length)
Total Length = Lcyl + Diameter (i.e. + 2r each end)
The first term, π × r² × Lcyl, is the volume of the straight cylindrical body. The second term, (4/3) × π × r³, is the volume of a complete sphere formed by the two hemispherical caps. The result in cubic centimetres is divided by 1,000 to get litres.
| Variable | Description | Example |
|---|---|---|
| D | Diameter of the tank | 1.2 m |
| r | Radius = D ÷ 2 | 0.6 m |
| Lcyl | Cylinder (body) length only | 2.0 m |
| Ltotal | Full end-to-end length | 3.2 m (= 2.0 + 1.2) |
| V | Total volume in m³ | π×0.36×2 + (4/3)×π×0.216 ≈ 3.166 m³ |
To convert to litres: multiply m³ by 1,000. To convert to US gallons: divide litres by 3.78541 — or, working in feet, multiply cubic feet by 7.48. To convert to UK/Imperial gallons: divide litres by 4.54609.
Not all domed ends are hemispheres. Many tanks and pressure vessels use shallower 2:1 ellipsoidal or torispherical (dished) heads. A 2:1 ellipsoidal head holds half as much as a hemisphere — (1/3) × π × r³ each — so for those tanks the end volume is (2/3) × π × r³ instead of (4/3) × π × r³, and this calculator would overstate the total. Check the head type on the data sheet.
Why hemispherical ends?
Domed ends distribute internal pressure evenly — no stress concentration at sharp corners. Critical for pressure vessels and buried tanks.
Same as a pill shape
A capsule tank has the same geometry as a pharmaceutical capsule — a cylinder sealed by two matching half-spheres of radius r.
Water weight
Fresh water weighs about 1 kg per litre (0.998 kg at 20 °C). For practical purposes, 1 litre ≈ 1 kg (2.2 lb) and 1 US gallon ≈ 8.34 lb.
When to Use a Capsule Tank Volume Calculator
Capsule-shaped tanks appear in a surprising variety of applications. Here's when this calculator is the right tool:
Road & Rail Tankers
Many liquid transport tanks (water, fuel, milk) are cylinders or ovals with domed or dished ends. For hemispherical ends this calculator gives the total capacity; for shallower heads, use the manufacturer's capacity chart.
Pressure Vessels
Compressed-air tanks, LPG cylinders, and hydraulic accumulators often have domed ends. Their rated (water) capacity is stamped on the vessel — use this calculator to understand it, not to replace the certified figure.
Underground Storage
Horizontal underground tanks for drinking water, diesel, or wastewater are often pill-shaped. Use this calculator for site planning and permitting.
Agricultural Tanks
Farm sprayer tanks and irrigation reservoirs frequently have oblong capsule shapes. Know your capacity for accurate chemical dilution ratios.
Fuel & Chemical Storage
Bulk fuel storage on remote properties and industrial chemical storage often use horizontal capsule tanks. Size correctly to avoid supply interruptions.
Residential Water Supply
Some domestic rooftop and under-slab tanks are manufactured with this shape for structural reasons. Calculate to match your household daily demand.
Worked example: a capsule tank in feet
A horizontal capsule tank is 4 ft (1.22 m) across inside and 10 ft (3.05 m) long from end to end.
- Cylinder length: total − diameter = 10 − 4 = 6 ft.
- Cylinder: π × 2² × 6 = 75.40 ft³.
- Two hemispherical ends (one sphere): (4/3) × π × 2³ = 33.51 ft³.
- Total: 108.91 ft³ × 7.48 = 815 US gallons (3,084 L, 678 UK gallons).
If the ends were 2:1 ellipsoidal instead, they would add only 16.76 ft³ and the straight shell would be longer for the same overall length, so always check which kind of head the tank has.
More Volume & Capacity Calculators
If your tank is a different shape, or you need downstream calculations, these tools will cover you:
Capsule Tank Volume — Frequently Asked Questions
A capsule tank — also called a pill tank — is a cylindrical vessel sealed at both ends with hemispherical (domed) caps. The result is a pill-like shape. Rounded ends spread internal stress far more evenly than flat ends, which is why domed ends are so common on pressure vessels, transport tanks and buried tanks. Many of those use shallower ellipsoidal or torispherical (dished) heads rather than full hemispheres, and hold a little less.
Total length is the full end-to-end measurement of the tank. Cylinder length (sometimes called body length or shell length) is only the straight cylindrical section, excluding both hemispherical caps. Because each cap has a height equal to the radius (r = Diameter ÷ 2), the relationship is: Cylinder Length = Total Length − Diameter. If you only have a tape measurement of the full tank, enter that in the "Total Length" field and this calculator will do the subtraction for you.
Use the formula: V = π × r² × Lcyl + (4/3) × π × r³. First calculate the radius (r = Diameter ÷ 2). Then multiply π × r² by the cylinder length to get the cylindrical body volume. Then add (4/3) × π × r³, which is the full-sphere volume contributed by the two hemispherical ends. The result in cubic centimetres, divided by 1,000, gives litres. The result in cubic metres, multiplied by 1,000, also gives litres.
Yes. The total volume is the same whether the tank is horizontal or vertical. The fill slider works as a percentage of total volume, not of depth; for a horizontal tank, the note under the results gives the exact contents at a quarter, half and three-quarters of the depth, using the circular-segment formula for the body plus a spherical cap for the ends. For other depths in a flat-ended tank, use our Horizontal Tank Volume Calculator.
Each measurement field independently supports feet (ft), inches (in), centimetres (cm), metres (m), and millimetres (mm). You can mix units — enter diameter in inches and length in feet, for example — and the calculator converts everything to centimetres internally before computing. Output is provided in litres, US gallons, UK/Imperial gallons, cubic metres, cubic feet, cubic inches, kilograms, and pounds.
Water weighs about 1 kg per litre (1,000 kg per cubic metre), or 8.34 lb per US gallon. This calculator outputs water weight in both kg and lbs directly. To find total weight, add the empty tank weight (from the manufacturer's spec sheet) to the water weight figure shown. For rooftop installations, also check our Rooftop Load-Bearing Calculator to confirm your structure can handle the combined load.
The geometric calculation is accurate regardless of the liquid. However, LPG (propane) tanks are filled to no more than about 80–85% of their water capacity to leave room for the liquid to expand — the fill limit is set by local gas regulations. For fuel tanks, the usable volume may also be slightly less than geometric volume due to baffles, pickup tube height, and sump geometry. Always verify with the manufacturer's rated capacity figure for critical applications.
Sources and review
The formula is standard geometry; the conversion factors and figures on this page come from these references:
- NIST Special Publication 811, Guide for the Use of the SI — US gallon (exactly 231 in³ = 3.785411784 L), cubic foot and cubic inch conversion factors.
- UK Weights and Measures Act 1985, Schedule 1 — the imperial gallon is exactly 4.54609 litres.
- USGS Water Science School — Water Density: about 1 kg per litre (62.4 lb/ft³, 8.34 lb per US gallon).
