Horizontal tank

Volume of a Horizontal Cylinder Calculator

A tank lying on its side needs segment maths, not a simple π r² h. Enter the liquid depth and get the true volume and fill percentage.

Horizontal tanks are the classic gotcha — half the depth is not half the volume. This volume of a horizontal cylinder calculator handles the geometry properly, giving you the liquid volume at any depth along with a fill gauge.

Horizontal tanks are common for fuel and water precisely because they are stable and easy to dip, but that convenience hides awkward geometry: the same rise in depth adds very different volumes near the bottom, middle and top.

Using the calculator

Measure the inside diameter and the length of the tank.
Measure the liquid depth straight down from the surface to the bottom.
The tool finds the filled circular-segment area from that depth.
It multiplies the segment area by the length for the liquid volume.
Read the fill percentage and remaining space.

Getting an accurate measurement

Take the depth straight down from the liquid surface to the bottom of the tank. Keep every measurement in the same system, and let the tool convert between units for you.

The maths in one line

The volume of a cylinder is:

V = π r² h

A worked example

Worked example. Take a cylinder with a diameter of 20 cm (so a radius of 10 cm) and a height of 40 cm. The base area is π × 10² = 314.16 cm², and multiplying by the height gives a volume of about 12.57 litres (12,566 cm³ · 3.32 US gallons).

This assumes flat ends and a level tank. Dished (curved) heads add a small amount of extra volume, so the flat-end result is slightly conservative.

Conversions use standard factors: 1 US gallon = 231 in³, 1 Imperial gallon = 4.54609 L, 1 litre = 1000 cm³.

After you have your answer

The figure above is usually the start, not the finish. These are the questions that tend to come next, answered here so you do not have to run another search:

Does it handle dished ends?

This assumes flat ends. Tanks with curved heads hold a little more, so treat the flat-end figure as a close, slightly conservative estimate.

How do I convert a dip reading to volume?

Measure the depth from the liquid surface to the bottom of the tank and enter it as the liquid depth; the tool converts that dip into a volume using the circular-segment area.

Why isn't half the depth half the volume?

Because a round tank is widest in the middle. At the halfway depth you are at exactly 50%, but above and below that the relationship curves, which is why a chart or this tool is needed.

What is the full capacity?

The result shows both the liquid volume at your depth and the full pi r squared times length capacity, so you can see exactly how much room is left.

Where people use this

It comes in handy across quite different tasks:

Dipping a horizontal fuel tank and converting depth to volume
Gauging a side-lying water tank between deliveries
Estimating remaining product in a cylindrical vessel

Getting it right

Two cautions with side-lying tanks: do not assume the depth-to-volume relationship is linear, and take the depth straight down to the lowest point. Curved tank ends hold marginally more than the flat-end estimate.

Getting the number in the unit you need

Because volume units are where most errors creep in, the tool does the converting for you. Enter your measurements once and every common unit appears together, from millilitres up to cubic metres and across to US and Imperial gallons. Pick whichever the task calls for and lift the rest from the list; nothing needs a second calculation. The result also updates live as you change a measurement, so you can compare two sizes quickly without starting over.

Related things you might need

Once you have your answer you may also want to work in tank capacity gallons hollow tube & pipe. These related calculators pick up where this one leaves off:

Volume of Horizontal Cylinder Calculator Cylinder on Its Side

To sum up, the whole job is two measurements and one formula. Enter them above, pick your unit, and you have an accurate figure plus every equivalent unit beside it. Keep a copy with the copy-result button, save the shareable link if someone else needs the same numbers, and use the history panel to compare a few options without starting from scratch.

Good to know

How do I measure the liquid depth?

Measure straight down from the top of the liquid to the bottom of the tank (a dip stick works well). Enter that depth and the inside diameter.

Does this include dished ends?

This mode assumes flat ends. Tanks with dished (curved) heads hold a little more; treat the flat-end figure as a close, slightly conservative estimate.

What is the formula for the volume of a cylinder?

The volume is V = π r² h — the area of the circular base (π r²) multiplied by the height (h). If you have the diameter instead of the radius, halve it first: r = d ÷ 2.

Do I use radius or diameter?

Either — just tell the calculator which you are entering. The radius is from the centre to the edge; the diameter is the full width across. The tool converts diameter to radius automatically.

What units can I use?

Any of millimetres, centimetres, metres, inches, feet or yards for the measurements, and you can read the result in litres, gallons, cubic feet, cubic inches and more.

Is the volume of a cylinder squared or cubed?

The result is in cubic units, because volume fills three dimensions. The radius is squared inside the formula only because it forms the flat circular base; multiplying by the height adds the third dimension.