- 1). Locate the cylinders. They're usually found near the top of the engine body, and the spark plugs connect to them.
- 2). Measure the diameter in centimeters of the interior of the cylinder inside its metal walls, using calipers. Don't round the number up or down; measure to a millimeter's range of accuracy. Record this number as "D" on a piece of paper.
- 3). Measure the depth of the interior of each cylinder, using the metric tape measure. Again, measure to a millimeter's accuracy. Record this number as "H" on your paper.
- 4). Count the number of cylinders on the motorcycle. If you have a twin engine, you'll have two sets of cylinders to locate and count. They should all be the same size, so you don't need to measure each one individually.
- 5). Calculate a cylinder's volume. To figure the area of a cylinder, you square its radius, multiply its height by pi, which is roughly 3.14. In this case, divide "D" by two to calculate the radius ("R"), and multiply the radius by itself. Take that number, multiply it by your cylinder depth ("H"), and multiply that by 3.14. This number is the volume of a single cylinder. Record that number as "V."
Cylinder Volume [V] = (D/2)x(D/2)xHx3.14
For example, a cylinder with a diamer of 36mm, and a depth of 50mm would have a volume of about 200cc [200 = (3.6)(3.6)x(5)x3.14] - 6). Multiply the cylinder volume by the number of cylinders you have in your engine to calculate your engine size. Engine size measures total displacement capacity across all cylinders in the engine.
Engine size = V x number of cylinders
So, a four-cylinder engine with 200cc cylinders has 800cc of displacement.
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