Calculate Cubic Inches of a Cylinder

Using the calculator

1. Measure across the circular end — the diameter or radius.
2. If you measured the diameter, halve it to get the radius r.
3. Square the radius and multiply by π to get the base area.
4. Multiply the base area by the height h: V = π r² h.
5. Convert the result into your preferred unit above.

Getting an accurate measurement

If you can only reach the top, measure the diameter across the opening and halve it. Keep every measurement in the same system, and let the tool convert between units for you.

The formula behind it

The volume of a cylinder is:

A worked example

Worked example. Take a cylinder with a diameter of 3 in (so a radius of 1.5 in) and a height of 8 in. The base area is π × 1.5² = 7.07 in², and multiplying by the height gives a volume of about 0.2 US gallons (57 in³ · 0.9 litres).

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

Follow-on questions, answered

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:

Is this the same as engine displacement?

For a single cylinder, yes: the bore radius and the stroke give the swept volume in cubic inches. Multiply by the number of cylinders for total displacement.

What is it in cc (cubic centimetres)?

One cubic inch is about 16.39 cc, so the cm3 figure in the breakdown is the metric version that engine builders usually quote.

How do I turn cubic inches into gallons?

Divide by 231 for US gallons — that is the exact definition of a US gallon — or by about 277.42 for Imperial. Both gallon values are shown with the result.

When this comes in handy

It comes in handy across quite different tasks:

• Blueprinting an engine's displacement
• Sizing a small precision reservoir
• Converting a machined bore to gallons

Where people go wrong

Two things trip people up: squaring the wrong number, and forgetting that the answer is cubic. If a result looks four times too big or too small, you have probably swapped radius and diameter somewhere, so it is always worth re-reading the measurement you are least sure of. It also helps to glance at the equivalent units; if the litre and gallon figures are both off by the same factor, the input is the culprit, not the maths.

Reading and converting your result

Showing every unit at once is about speed and safety: you see the answer in litres, gallons and cubic feet side by side, so there is no chance of applying the wrong conversion factor. Change the output unit at the top to make any of them the headline figure, switch the precision to exact if you want the value in terms of pi, and use copy-result to paste a tidy summary wherever you need it.

Keep going

Once you have your answer you may also want to work in gallons cubic feet volume formula. These related calculators pick up where this one leaves off:

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.

Questions people ask