Tank Volume Calculator
Capacity and filled volume of horizontal or vertical cylinder, rectangular, capsule, cone-bottom and spherical tanks, with a dip chart in litres, gallons or bbl.
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About this toolWhat is the Tank Volume Calculator?
How much is in the tank? For a box or an upright cylinder that is easy, but a horizontal cylinder or a sphere fills unevenly: the first and last few centimetres hold very little, the middle holds a lot. This calculator handles seven shapes, works out the total capacity, and gives the liquid volume at any depth measured from the lowest point. With the defaults, a 2 m diameter horizontal tank 5 m long holds 15,708 L, and 500 mm of liquid in it is only 3,071 L, under 20% of capacity at 25% of the height.
Shapes are horizontal and vertical cylinders with flat ends, rectangular tanks, horizontal and vertical capsules with hemispherical ends, vertical cylinders with a cone bottom, and spheres. Dimensions go in mm, cm, m, inches or feet; volumes come out in litres, cubic metres, US gallons, UK gallons, cubic feet or oil barrels.
Two extras make it a working tool rather than a one-off sum. You can type a target volume and get the depth that holds it, which is handy for marking a level gauge. And the dip chart (strapping table) lists volume and percent full at any depth step you choose, with a chart of volume against depth.
- Seven shapes: horizontal and vertical cylinder, rectangular, horizontal and vertical capsule, cone bottom and sphere
- Filled volume, percent full and ullage at any depth
- Depth for a target volume, solved numerically
- Dip chart table and volume-depth chart at any step
- Litres, m³, US and UK gallons, ft³ and oil barrels with exact conversions
How to use the Tank Volume Calculator
- Choose the tank shape.
- Pick a length unit and a volume unit, then enter the inside dimensions. Each shape asks only for what it needs.
- Enter the liquid depth measured from the lowest point of the tank to read the filled volume, percent full and remaining space.
- Optionally type a target volume to get the depth that holds it.
- Set the dip chart step to your dipstick graduation (for example 50 mm or 1 inch) to build the strapping table, then copy or print it.
Worked examples
Horizontal diesel or water tank
Input
2,000 mm diameter, 5,000 mm long, 500 mm depth
Output
Capacity 15,708 L; 3,070.9 L at 500 mm (19.55% full)
Reading 25% on a dipstick and assuming 25% full would overstate the contents by about 860 L.
48 × 120 inch fuel tank in US gallons
Input
48 in diameter, 120 in long
Output
940 US gal full; 183.8 gal at 12 in, 470 gal at 24 in, 756.3 gal at 36 in
A 1 inch dip chart step gives a 49-row table ready to tape inside a fill cabinet.
Cone-bottom hopper tank
Input
3 m diameter, 4 m cylinder, 1.5 m cone
Output
Capacity 31.81 m³; cone alone holds 3.53 m³; 14.14 m³ at 3 m depth
The cone holds little volume for its height, so the bottom of a level gauge moves fast as it drains.
Background and insight
A horizontal cylinder's partial volume is the area of a circular segment times the length: A = r² cos⁻¹((r − h)/r) − (r − h)√(2rh − h²). The same segment geometry, rotated, gives the spherical cap V = πh²(3r − h)/3 used for spheres and for the hemispherical ends of capsule tanks. A cone bottom fills as a smaller cone until the liquid reaches the cylinder.
Because the segment area is not linear in depth, rules of thumb mislead. At a quarter of the diameter a horizontal cylinder is 19.6% full, at half it is exactly 50% and at three quarters it is 80.4%. A sphere at a quarter of its height is only 15.6% full.
Unit factors are exact: 1 US gallon is 3.785411784 L, 1 imperial gallon 4.54609 L, and an oil barrel 42 US gallons (158.987 L). For custody transfer and tax purposes, tanks are calibrated by recognised strapping methods such as API MPMS Chapter 2 rather than from nominal drawings, because real tanks have dished heads, slopes, dents and internal fittings.
Common use cases
Fuel and oil inventory
Turn a dipstick reading into litres or gallons for heating oil, diesel or lube tanks.
Water storage and rainwater tanks
Find capacity and remaining days of supply from the water level.
Level gauge marking
Get the depth for 25%, 50% or any volume to mark a sight glass or set level switches.
Process vessels and hoppers
Volume in capsule and cone-bottom vessels at any fill, for batching and dosing.
Tips and limitations
- Use inside dimensions. Wall thickness on a large steel tank can change the capacity by a percent or more.
- Measure depth from the lowest inside point. If the dipstick rests on a sump or a drain boss, subtract that height.
- Dished torispherical or ellipsoidal heads hold less than the hemispherical ends this tool models; treat capsule results as an upper bound for those.
- A tank on a slope reads differently at each end. Level it or dip at the centre.
- Leave headroom for thermal expansion and foam. Fuel tanks are typically filled to about 90 to 95% of capacity.
Frequently asked questions
How do you calculate the volume of a horizontal cylindrical tank?
Full volume is πr²L. For a partial fill at depth h, multiply the circular segment area, r² cos⁻¹((r − h)/r) − (r − h)√(2rh − h²), by the length L. A 2 m diameter, 5 m tank at 0.5 m depth holds 3.071 m³.
How many gallons are in a cylindrical tank?
Compute πr²L in cubic inches and divide by 231 for US gallons. A tank 48 in across and 120 in long holds π × 24² × 120 / 231 = 940 US gallons.
What is a tank dip chart?
A table that converts a measured liquid depth into volume for one specific tank. It is also called a strapping table or calibration chart. This calculator builds one at any step you choose.
Why is a half-full horizontal tank not half the volume at other depths?
The width of the liquid surface changes with depth: narrow at the bottom and top, widest in the middle. Volume therefore rises slowly, then quickly, then slowly again. Only at exactly half the diameter is it exactly 50%.
How do I find the volume of a cone-bottom tank?
Add the cone, πr²h_c/3, to the cylinder, πr²h. Below the top of the cone the liquid forms a smaller cone whose radius scales with depth: V = π(r h/h_c)² h/3.
How do I convert tank volume to litres or barrels?
1 m³ = 1,000 L; 1 US gallon = 3.785 L; 1 imperial gallon = 4.546 L; 1 oil barrel = 42 US gallons = 158.99 L. Choose the volume unit in the calculator and all results convert.
Is there an in-depth guide to the Tank Volume Calculator?
Yes. “Tank Volume Formulas and Dip Charts for Horizontal, Vertical and Odd Shapes” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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