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Cylinder volume — questions & answers

The questions that come up most often about calculating cylinder volume and capacity.

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.
How many gallons are in a cylinder?
Work out the volume with V = π r² h, then convert. One US gallon is 231 cubic inches; one Imperial gallon is about 277.42 cubic inches. The calculator does both for you.
What is the difference between US and Imperial gallons?
An Imperial gallon (about 4.546 litres) is larger than a US gallon (about 3.785 litres). Always confirm which one you need — the tool shows both so you can't mix them up.
How do I find the volume of a cylinder in litres?
Calculate V = π r² h in consistent units, then convert to litres — one litre is 1000 cm³, or one cubic decimetre. Enter your measurements above and the litre figure appears automatically.
How many litres is one cubic metre?
Exactly 1000 litres. The calculator shows the cubic-metre value beside the litre value so you can switch between them at a glance.
What is the cylinder volume formula?
V = π r² h. Using diameter, it becomes V = π (d/2)² h, which is the same as V = π d² h ÷ 4.
What does each symbol mean?
V is volume, r is the radius of the circular base, h is the height (or length), and π is about 3.14159. The radius and height must be in the same unit before you multiply.
How do I calculate the volume of a cylindrical tank?
For an upright tank, use V = π r² h with the inside radius and the liquid height. The calculator also shows full capacity and the space left empty.
How do I find how full my tank is?
Enter the tank's inside diameter and the current liquid height. The tool returns the liquid volume, the full capacity and the fill percentage.
Why can't I use π r² h for a horizontal tank?
Because a tank on its side fills as a circular segment, not a simple stack. Half the depth is not half the volume. The calculator uses the correct segment formula.
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.
How do I find the volume of a hollow cylinder?
Subtract the inner cylinder from the outer one: V = π h (R² − r²), where R is the outer radius and r is the inner radius. The tool asks for diameters and does the halving for you.
What is the difference between material volume and capacity?
Material volume is the solid in the wall; capacity is the empty space in the bore. A pipe's coating budget uses material volume; what it carries uses the bore capacity.

Still stuck? The formula page walks through the maths, and the full list of calculators has a tool for almost every specific case.