Tank Volume Calculator
Calculate the internal capacity, current liquid volume and empty space in rectangular, vertical cylindrical and horizontal cylindrical tanks. Choose independent measurement units, account for flat or hemispherical ends, and convert the result to litres, gallons or cubic units.
- Four tank models
- Full or partial fill
- Mixed dimension units
- Optional liquid mass
Calculate Tank Capacity and Liquid Level
Use internal dimensions. Select the tank model that matches the real geometry, then enter a fill depth or calculate full capacity.
Rectangular tank, partial fill
Equivalent filled volume
| Unit | Value | Definition used |
|---|---|---|
| Litres | 288 L | 1 L = 0.001 m³ |
| Cubic metres | 0.288 m³ | SI volume unit |
| US liquid gallons | 76.08 US gal | 3.785411784 L |
| Imperial gallons | 63.35 imp gal | 4.54609 L |
| Cubic feet | 10.17 ft³ | 28.316846592 L |
Calculation steps
- Convert internal dimensions to metres: 1.2 m, 0.6 m and 0.5 m.
- Total capacity = 1.2 x 0.6 x 0.5 = 0.36 m3.
- Convert fill depth: 40 cm = 0.4 m.
- Filled volume = 1.2 x 0.6 x 0.4 = 0.288 m3.
- 0.288 m3 x 1000 = 288 L.
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Recent calculations
How to Use This Tank Volume Calculator
Allow about two minutes to identify the tank geometry, enter internal measurements and review the assumptions behind the result.
- Select the tank shape. Choose a rectangular tank, vertical cylinder, horizontal flat-ended cylinder or horizontal cylinder with two hemispherical ends.
- Choose full or partial fill. Select full capacity when the tank is completely filled, or partial fill when you know the vertical liquid depth.
- Enter internal dimensions. Add each measured value with its own unit. For round tanks, choose diameter, radius or circumference before entering the circular measurement.
- Describe rounded ends correctly. For a hemispherical-ended tank, state whether the entered axial length is the straight cylindrical section or the overall end-to-end length.
- Set result options. Choose a volume unit and decimal places. Add a verified liquid density only when you also need an estimated mass.
- Calculate and review. Check capacity, filled volume, remaining space, fill percentage, equivalent units, diagram and calculation steps before using the estimate.
The value boxes accept decimals, scientific notation, simple fractions and mixed numbers. Every physical tank dimension must be positive. A liquid depth of zero is valid, but a depth above the tank's internal height or diameter is rejected.
Tank Volume Formulas
All formulas use internal dimensions. Let L be length, W width, H height, r internal radius and h vertical liquid depth. The calculator converts every dimension to metres before applying the selected geometry.
| Tank model | Full capacity | Filled volume |
|---|---|---|
| Rectangular tank | C = LWH | V = LWh |
| Vertical cylinder | C = πr2H | V = πr2h |
| Horizontal flat-ended cylinder | C = πr2L | V = AsegmentL |
| Horizontal hemispherical-ended tank | C = πr2L + 4πr3/3 | V = AsegmentL + Vsphere segment |
In the hemispherical-ended formula, L is the straight constant-diameter section between the two tangent lines. Overall internal length equals L + 2r. The calculator can derive L when you enter overall length.
For a horizontal circular cross-section, the direct segment-area formula is:
For two hemispherical ends, the ends together form one sphere. The volume below liquid depth h is the spherical-cap expression πh2(r - h/3) when the level is at or below the centreline. Above the centreline, the calculator subtracts the small empty cap from the complete sphere. This complementary form avoids subtracting nearly equal numbers at the wrong stage.
Why Horizontal Tank Depth Is Not a Volume Percentage
A vertical-sided rectangular tank and a vertical cylinder have a constant horizontal cross-section. Their volume percentage therefore matches the liquid-depth percentage. If a vertical cylinder is 60% deep, it is also 60% full by geometric volume.
A horizontal cylinder behaves differently. Its cross-section is narrow near the bottom, widest at the centreline and narrow again near the top. A liquid depth equal to 25% of the diameter occupies only about 19.55% of a flat-ended horizontal cylinder. At half the diameter, symmetry gives exactly half the capacity. At 75% depth, the volume is about 80.45%.
The direct circular-segment equation loses numerical accuracy when the depth is extremely close to empty or full. This calculator evaluates a small-segment series near the boundary and uses the complementary empty segment above the centreline. It handles exact empty, half-full and full states separately. These steps keep tiny positive volumes positive and make filled volume plus remaining volume agree with total capacity within floating-point limits.
Tank Volume Examples
Example 1: Rectangular aquarium
An aquarium has internal dimensions of 120 cm by 60 cm by 50 cm. Its full internal capacity is 360,000 cm³, which equals 360 L. If the water depth is 40 cm, the water volume is 120 × 60 × 40 = 288,000 cm³, or 288 L. The aquarium is 80% full and has 72 L of geometric space above the water.
Example 2: Vertical cylindrical water tank
A vertical tank has an internal diameter of 2 m and height of 3 m. Its radius is 1 m. Full capacity is π × 12 × 3, approximately 9.42478 m³ or 9,424.78 L. At a depth of 1.5 m, it contains half that volume, approximately 4,712.39 L.
Example 3: Part-filled horizontal cylinder
A flat-ended horizontal tank has a 2 m internal diameter, 4 m internal length and liquid depth of 0.5 m. The circular-segment area is approximately 0.614184849 m². Multiplying by the 4 m length gives approximately 2.456739397 m³, or 2,456.74 L. Although the depth is 25% of the diameter, the tank is only about 19.55% full.
Example 4: Horizontal tank with hemispherical ends
Consider a 2 m diameter tank with a 4 m straight cylindrical section and two hemispherical ends. The cylindrical section holds approximately 12.56637 m³. The two ends together hold the volume of a 1 m radius sphere, approximately 4.18879 m³. Total geometric capacity is therefore approximately 16.75516 m³. At the centreline, the symmetric tank is exactly 50% full by volume.
Tank Capacity Units and Liquid Mass
The calculator keeps geometry in cubic metres, then converts the final volume with defined factors. One cubic metre equals exactly 1,000 L. One international cubic foot equals exactly 28.316846592 L. One U.S. liquid gallon equals exactly 3.785411784 L, while one Imperial gallon equals exactly 4.54609 L. The two gallon systems are not interchangeable.
| Volume unit | Exact relationship | Use note |
|---|---|---|
| Cubic metre | 1 m³ = 1000 L | SI volume unit |
| Cubic centimetre | 1 cm³ = 1 mL | Useful for small containers |
| Cubic foot | 1 ft³ = 28.316846592 L | Uses the international foot |
| U.S. liquid gallon | 1 US gal = 3.785411784 L | Not an Imperial gallon |
| Imperial gallon | 1 imp gal = 4.54609 L | U.K. statutory definition |
| Petroleum barrel | 1 bbl = 42 US gal | Other barrel definitions differ |
Liquid mass equals volume multiplied by density. Density is not a universal property of “liquid.” It depends on the substance and can change with temperature, concentration and pressure. Enter a verified value in kg/m³, g/cm³, kg/L, lb/ft³ or lb/US gal. The calculator does not silently assume water.
Internal Dimensions, Usable Capacity and Accuracy
External tank dimensions include wall thickness and do not directly describe internal capacity. Use internal length, width, height and diameter. For a tank with insulation, liners, thick walls or double containment, a simple external measurement can overstate capacity materially.
The result is a geometric estimate. Real usable volume can be lower because of freeboard, bottom slope, internal piping, coils, baffles, supports, fittings, rounded corners, sediment, deformation or an unusable heel below the outlet. A tank that is tilted changes the relationship between liquid depth and volume. Temperature also changes both tank dimensions and liquid volume.
Hemispherical-ended mode assumes two complete half-sphere ends joined tangentially to a constant-diameter cylinder. It does not represent 2:1 ellipsoidal, torispherical, flanged-and-dished, conical or irregular heads. Those shapes require their actual head dimensions and, for many industrial tanks, manufacturer drawings or a calibrated capacity table.
Do not use this page as a custody-transfer gauge, legal-metrology table, pressure-vessel design, overfill-protection setting or hazardous-material operating limit. For commercial inventory, regulated storage or safety-critical work, use approved measurements, current standards, calibrated strapping tables and qualified review.
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Frequently Asked Questions
What is the basic formula for tank volume?
Tank volume equals cross-sectional area multiplied by length or height for a uniform prism. A rectangular tank uses L x W x H. A right circular cylinder uses pi x r squared x H. Partial horizontal cylinders require a circular-segment area.
How do I calculate the litres in a rectangular tank?
Multiply internal length, width and filled depth using one consistent length unit. If all three are in centimetres, the result is cubic centimetres. Divide by 1,000 because 1,000 cubic centimetres equal exactly 1 litre.
How is a vertical cylindrical tank calculated?
Divide internal diameter by two to get radius. Full capacity is pi x radius squared x internal height. For a partial fill, replace total height with the measured liquid depth because the horizontal cross-section stays constant.
How is a partially filled horizontal tank calculated?
The liquid cross-section is a circular segment. Its area depends on internal radius and vertical liquid depth, then the area is multiplied by the straight tank length. A depth percentage alone does not give the correct volume percentage.
What does hemispherical-ended tank mode include?
It models a constant-diameter horizontal cylinder with one hemisphere at each end. The ends together form one sphere. It does not model ellipsoidal, torispherical, conical or irregular heads.
Should I enter internal or external tank dimensions?
Use internal dimensions for liquid capacity. External dimensions include walls, liners, insulation or double containment and can overstate the usable interior. Use manufacturer data when internal dimensions cannot be measured safely.
Is one cubic centimetre equal to one millilitre?
Yes. One cubic centimetre equals exactly one millilitre. One litre equals exactly one cubic decimetre, and one cubic metre equals exactly 1,000 litres.
Are U.S. and Imperial gallons the same?
No. One U.S. liquid gallon equals exactly 3.785411784 litres. One Imperial gallon equals exactly 4.54609 litres. Choose the named system required by your tank record or specification.
Does 25% liquid depth mean a horizontal tank is 25% full?
No. In a flat-ended horizontal cylinder, 25% of diameter as depth is about 19.55% of volume. The cross-section widens toward the centreline. Half the diameter does equal 50% volume because the shape is symmetric.
Can this result replace a calibrated tank chart?
No. This is a geometric estimate. Tilt, head geometry, wall shape, fittings, internal structures, deformation and temperature can change real capacity. Commercial, regulated or safety-critical use requires approved measurements and calibrated tables.
Method and Official Sources
Rectangular-prism and cylinder relationships follow NASA Glenn volume guidance and OpenStax geometry formulas. SI volume relationships and unit symbols follow NIST SI Units: Volume. U.S., Imperial and cubic conversion factors follow NIST SP 811, Appendix B and NIST Handbook 44, 2026, Appendix C.
For calibrated horizontal tank work, ISO 12917-1:2017 covers manual methods for nominally horizontal cylindrical tanks and identifies geometry, head shape and tilt as relevant calibration details. This page implements only the explicitly listed ideal shapes.
Measurement note: This calculator provides an informational geometric estimate. It does not certify tank capacity, safe fill level, structural adequacy, pressure rating, overfill protection, legal measurement, hazardous-material compliance or usable operating volume.