Find out how much a tank can hold and how much liquid is in it right now. Choose a horizontal cylinder, vertical cylinder, rectangular or spherical tank, enter its inside dimensions and the liquid depth or the percentage full, and read the volume in litres and US gallons together with the weight of the liquid.
Use inside dimensions. The picture and results update as you type.
A tank’s total capacity depends only on its shape and inside size, but the liquid it holds depends on the depth. For a vertical cylinder or a rectangular tank the liquid volume grows in a straight line with depth, so half the depth is half the volume. For a horizontal cylinder or a sphere the cross-section is a circle, so the volume grows slowly near the bottom, fastest around the middle and slowly again near the top. That is why a dipstick on a round tank needs a calibrated scale instead of evenly spaced marks.
Enter the inside diameter and length (or height) of the tank, then either the depth of the liquid measured from the lowest inside point, or the percentage you want to reach. The calculator returns the liquid volume, the tank capacity, the empty space and, if you pick a liquid, its weight. It treats the ends of the tank as flat. For the full volume and surface area of a shape, the 3D Shape Calculator shows each formula with your numbers.
| Tank | Total capacity | Liquid at depth h |
|---|---|---|
| Horizontal cylinder | πr²L | L × [r² arccos((r − h)/r) − (r − h)√(2rh − h²)] |
| Vertical cylinder | πr²H | πr²h |
| Rectangular tank | l × w × H | l × w × h |
| Spherical tank | (4/3)πr³ | πh²(3r − h)/3 |
Here r is the inside radius, L the length of a horizontal tank, H the inside height, and h the depth of the liquid. Angles in the arccos are in radians.
Horizontal heating-oil tank. A tank with an inside diameter of 1.2 m (r = 0.6 m) and a length of 3 m holds π × 0.6² × 3 ≈ 3.393 m³, which is 3,393 litres or 896 US gallons. With 0.5 m of liquid the formula gives 1.338 m³, or 1,338 litres (39.4% full). The liquid reaches about 42% of the tank’s height but fills only about 39% of its capacity, because the bottom of a round tank is narrow.
Vertical water tank. A cylinder 1.5 m across and 2 m high filled to 1.2 m holds π × 0.75² × 1.2 ≈ 2.121 m³, about 2,121 litres. Because the sides are straight, 60% of the height is exactly 60% of the volume.
Rectangular tank. A tank 2 m long and 1 m wide filled to 0.6 m contains 2 × 1 × 0.6 = 1.2 m³, or 1,200 litres.
Spherical tank. A sphere 2 m across (r = 1 m) filled to a depth of 0.8 m holds π × 0.8² × (3 × 1 − 0.8) / 3 ≈ 1.474 m³, or 1,474 litres.
How do I calculate how much liquid is in a horizontal cylinder tank? Measure the diameter, the length and the depth of the liquid from the bottom of the tank. The partial volume is L × [r² × arccos((r − h)/r) − (r − h) × √(2rh − h²)], where r is the radius and h is the liquid depth. The calculator does this for you and also gives litres, gallons and the percentage full.
Why is a half-full depth exactly half the volume in a round tank? In a horizontal cylinder or a sphere, a liquid depth of exactly half the diameter fills exactly half of the volume because of symmetry. At other depths the relationship is not linear: a horizontal tank filled to a quarter of its diameter holds only about 19.6% of its capacity.
How do I find the depth for a given percentage full? Change the fill input to Percent full and type the percentage. The calculator then works backwards and shows the liquid depth, which is handy when you want to mark a dipstick or a sight gauge.
Does the calculator allow for domed or sloped tank ends? No. It treats every tank as a plain shape with flat ends, so a tank with domed or dished heads holds slightly more than the result. For a close estimate, measure the tank body and add the volume of each head separately, for example with the Spherical Cap Volume Calculator.
Should I measure inside or outside dimensions? Use the inside dimensions. The wall thickness of steel, plastic or concrete reduces the space available for liquid, and ignoring it overstates the capacity.
How are litres and US gallons related to cubic metres? One cubic metre equals 1,000 litres, and one US liquid gallon is about 3.785 litres. The calculator shows all of these for both the tank capacity and the liquid inside.