Tankmeasure / Calculation guide
Calculation guide
A dip reading becomes a volume only when you know the tank’s shape. This guide explains the internal measurements, the curved-cylinder calculation and the differences between geometric capacity and liquid you can actually draw out.
1. Choose the matching shape
Rectangular: a box-shaped tank with straight sides and a level, flat bottom. Vertical cylinder: a round tank standing on a flat circular bottom. Horizontal cylinder: a circular cylinder lying lengthwise, with flat ends. Select another method for oval sections, domed ends, cones or a deliberately sloping base.
Measure every dimension inside the tank. Diameter is the full distance across a circular section, not the radius. Fill depth is the vertical distance from the lowest internal bottom to the liquid surface. If you measured the air gap from the top, subtract that gap from the internal height first.
2. Rectangular and vertical-cylinder formulas
Vertical cylinder filled volume = π × radius² × liquid depth
Capacity = the same formula using total internal height
The calculator converts inputs to metres before calculating cubic metres. It then multiplies by 1,000 for litres. One cubic metre equals 1,000 litres. Feet use 0.3048 metres per foot; inches use 0.0254 metres per inch.
Worked example: a rectangular tank
Internal length 2.4 m, width 1.2 m and height 1.1 m give 3.168 m³ or 3,168 L total geometric capacity. At a depth of 0.55 m, liquid volume is 2.4 × 1.2 × 0.55 = 1.584 m³ or 1,584 L. The same amount of space remains, so the tank is 50% full.
Worked example: a standing round tank
An internal diameter of 2 m gives a radius of 1 m. At 0.75 m liquid depth, volume is π × 1² × 0.75 = approximately 2.3562 m³ or 2,356.2 L. If the internal height is 1.5 m, capacity is about 4,712.4 L and the tank is half full.
3. A horizontal cylinder needs the curved segment
For a horizontal tank, multiply the filled area of the round end by the straight tank length. The filled area changes nonlinearly with depth.
Filled volume = A × length
r = internal radius; h = liquid depth; angles are in radians
The implementation uses an equivalent angle formula and a small-angle series near empty, then symmetry above half full. This avoids losing precision when the segment is very shallow. Depth must be between zero and the internal diameter.
Worked example: quarter depth is not quarter volume
Take a cylinder with a 2 m internal diameter and 3 m straight length. Total capacity is π × 1² × 3 = about 9,424.8 L. At a 0.5 m depth, the filled end area is about 0.6142 m², giving 1,842.6 L or 19.55% full. At 1 m depth it is exactly half full: about 4,712.4 L.
4. What this estimate leaves out
The result assumes a level tank and ideal geometry with a still, level liquid surface. Internal pipes, wall ribs, baffles, sediment, rounded corners and end caps can change the actual liquid volume. A delivery label may describe nominal, safe-fill or usable capacity rather than the full geometric volume. Manufacturer calibration tables are a better match for shaped tanks.
This tool calculates volume, not mass, pressure, safe loading, liquid quality or a tank’s suitability for any particular substance. For an irregular tank, start from the manufacturer’s dimensions and calibration data rather than forcing it into the closest shape.
Frequently asked questions
Can I enter centimetres or inches?
Yes. Choose a unit first, then use it for every dimension. Changing units converts the current entries; it does not reinterpret the same numbers as a different physical size.
Why is the remaining space different from usable storage?
Remaining space is full geometric capacity minus liquid volume. It does not subtract a required air gap, unusable bottom volume or a fill-line limit.
Are the results stored?
The calculator runs in your browser. It does not upload dimensions or create an account. Printing uses your browser’s print controls. Read the privacy information for hosting and contact details.