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 outer diameter (or inner diameter if you need net volume) of the cylindrical section. 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 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. To convert to UK/Imperial gallons: divide by 4.54609.
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
Pure water weighs exactly 1 kg per litre at 4°C. For practical purposes, 1 litre ≈ 1 kg and 1 US gallon ≈ 8.34 lbs.
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
Most liquid transport tankers (water, fuel, milk) use a capsule cross-section. Calculate the total capacity or remaining volume for logistics planning.
Pressure Vessels
Compressed-air tanks, LPG cylinders, and hydraulic accumulators commonly use this geometry. Accurate volume is needed for safety compliance.
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.
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, oblong tank, or torispherical tank — is a cylindrical vessel sealed at both ends with hemispherical (domed) caps. The result is a pill-like shape. This geometry is extremely common for pressure vessels, transport tankers, and underground water storage because the rounded ends distribute internal stress far more evenly than flat or flanged ends.
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 volume formula for a capsule tank is the same whether the tank is oriented horizontally or vertically — the geometry is identical. The fill level slider gives you an approximation of partial fill volume. For precise partially-filled horizontal cylinder calculations (where the cross-section exposed to liquid changes with depth), 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 1 kg per litre (1,000 kg per cubic metre) at standard conditions. 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, for LPG and other compressible gases stored as liquids, be aware that the usable capacity is typically 80–85% of geometric volume (ullage allowance for expansion). 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.