What the inputs mean
- Bore: the diameter of each cylinder.
- Stroke: how far the piston travels from top dead center to bottom dead center. It is twice the crankshaft throw.
- Cylinders: the number of cylinders that share that bore and stroke.
Switch between US and metric units at the top of the page. Bore and stroke are in inches in US units and in millimetres in metric; the results always show cc, liters and cubic inches.
The displacement formula
Each cylinder sweeps a cylinder of air as the piston travels from top to bottom. Its volume is the area of the bore times the stroke:
displacement = π ÷ 4 × bore² × stroke × cylinders
1 cubic inch = 16.387064 cc 1 liter = 1,000 ccWith bore and stroke in inches you get cubic inches. With bore and stroke in millimetres, divide by 1,000 to get cc.
Worked example
A V8 with a 4.000 in bore and a 3.480 in stroke:
- One cylinder: π ÷ 4 × 4.000² × 3.480 = 43.73 ci.
- Eight cylinders: 43.73 × 8 = 349.8 ci, which is 5,733 cc or 5.73 liters.
Bored 0.030 in over, to 4.030 in, the same engine comes to 355.1 ci (5,819 cc). The overbore adds 86 cc, or 1.5%. Displacement grows with the square of the bore, so small bore changes add up quickly across eight cylinders.
In metric: a four-cylinder with an 86 mm bore and an 86 mm stroke gives 1,998 cc, 2.00 liters or 121.9 ci.
Bore to stroke ratio
The calculator also shows bore divided by stroke. Above 1 the engine is oversquare (bore larger than stroke), below 1 it is undersquare. It describes the shape of the cylinder; it does not change the displacement.
Why engine sizes are rounded
Advertised sizes are usually rounded, and the rounding differs between cubic inches and liters. That is why the same engine can be quoted as a round cubic inch number and a liter figure that does not convert exactly. For the true size, use the measured bore and stroke.
Questions
How do I calculate engine displacement?
Multiply π ÷ 4 by the bore squared, then by the stroke and the number of cylinders. A 4.000 in bore, 3.480 in stroke V8 gives 349.8 cubic inches, which is 5,733 cc.
How much displacement does a 0.030 overbore add?
It depends on the bore, stroke and cylinder count. On a 4.000 in bore, 3.480 in stroke V8, going 0.030 in over adds 5.3 ci (86 cc), about 1.5%. Going 0.040 in over adds 7.0 ci (115 cc), about 2.0%.
How many cc are in a cubic inch?
One cubic inch is exactly 16.387064 cc, because an inch is defined as 25.4 mm. A liter is 1,000 cc, or about 61.02 cubic inches.
Does the stroke or the bore matter more for displacement?
The bore counts twice because it is squared, so a 1% larger bore adds about 2% displacement, while a 1% longer stroke adds 1%.