Understanding your result
Liquid volume and unfilled space are reported in litres, with a US-gallon conversion. Filled percentage describes volume, which is not generally the same percentage as depth in a horizontal cylinder.
Convert a pump or filling rate to compatible volume units with the Flow Rate Converter .
The formula
A horizontal cylinder contains a circular segment of liquid at each cross-section. At half diameter the tank is half full, but away from that point the depth-to-volume relationship is curved. The full cylinder capacity is πr² times its axial length.
Worked example
A horizontal cylinder with internal diameter 1 m and length 2 m holds about 1,570.796 L when full. At a liquid depth of 0.5 m it holds half that amount, approximately 785.398 L.
How to use this calculator
- Choose the tank shape and use one dimension unit throughout.
- Measure internal dimensions, excluding wall thickness.
- Enter liquid depth measured vertically from the inside bottom.
- Compare liquid volume with full capacity and unfilled space.
Why shallow depth is not a linear gauge
In a horizontal cylinder, the wetted width grows as liquid rises toward the centre. The same extra centimetre of depth therefore represents different volumes at different levels. A rectangular tank and a vertical cylinder have constant horizontal cross-sections, so their fill volume changes linearly with depth.
Match the vessel geometry
The cylindrical modes assume flat ends. Rounded, dished, conical, or ellipsoidal ends need different volume calculations. Internal baffles, pipes, sediment, and required operating headspace also reduce usable storage. For ordering or metering, compare the geometric estimate with the manufacturer’s calibration chart rather than assuming the external nominal dimensions equal internal capacity.
Assumptions & limitations
What this calculation assumes
- The tank is level, rigid, and described by the selected ideal geometry.
What to keep in mind
- No domed ends, tilt correction, liquid expansion, wall thickness deduction, or manufacturer calibration.
Common questions
Are these US or Imperial gallons?
The gallon result is explicitly US liquid gallons. An Imperial gallon has a different size.
Can I use external tank measurements?
Only as an approximation. Internal dimensions are needed for actual geometric capacity; wall thickness and internal fittings occupy space.