Displacement is the volume a piston sweeps between bottom dead centre and top dead centre, multiplied by the number of cylinders. The bore gives the cross-sectional area of the cylinder and the stroke gives the distance the piston travels, so the swept volume of one cylinder is simply area times length. Nothing about valve timing, boost or compression enters into it.
The area of a circle from its diameter is pi over four times the diameter squared, so the formula is pi/4 x bore squared x stroke x cylinders. With bore and stroke in millimetres the result is in cubic millimetres, and dividing by 1000 converts to cubic centimetres. For an 84 mm bore and 90 mm stroke that is 498.76 cc per cylinder.
Across 4 cylinders that gives 1995.0 cc, which the marketing department will call 2.0 litres. In American units it is 121.7 cubic inches, since one cubic inch is exactly 16.387064 cc. The bore-to-stroke ratio of 0.933 makes this a slightly undersquare engine, which tends towards low-end torque rather than high-rpm power.
The formula
bore- Cylinder diameter in millimetres
stroke- Piston travel from bottom to top dead centre, in millimetres
cylinders- Number of cylinders
÷ 1000- Converts cubic millimetres to cubic centimetres
How to use this calculator
- Enter the bore and stroke, and set the unit selector to millimetres or inches.
- Enter the number of cylinders.
- Enter the compression ratio if you want the implied clearance volume.
- The gauge shows total displacement in cc; litres, cubic inches and the bore-stroke ratio sit below.
Worked examples
84 mm bore, 90 mm stroke, 4 cylinders
One cylinder sweeps pi/4 x 84² x 90 = 498,759 cubic millimetres, which is 498.76 cc. Across 4 cylinders that is 1995.0 cc, or 2.00 litres and 121.7 cubic inches.
A long-stroke straight six
An 86 mm bore with a 96 mm stroke across six cylinders gives 557.65 cc per cylinder and 3346 cc in total — 3.35 litres. The bore-stroke ratio of 0.896 is clearly undersquare, favouring torque over peak revolutions.
How to read your score
Frequently asked questions
Why is bore squared but stroke is not?
Because the bore sets an area and the stroke sets a length. Doubling the stroke doubles the volume, but doubling the bore quadruples it. That is why manufacturers chasing capacity within a fixed block usually reach for a longer stroke — the bore is limited by cylinder spacing.
What does oversquare or undersquare mean?
Oversquare means the bore exceeds the stroke, giving lower piston speed at a given rpm and room for bigger valves, which suits high-revving power. Undersquare means a longer stroke, which produces more torque lower down but limits safe maximum revs.
Is this the same as the advertised engine size?
It is the honest figure; the advertised one is rounded. An engine calculating at 1995 cc will be sold as a 2.0 litre, and a 1798 cc engine is marketed as an 1.8. The rounding is sometimes generous by 50 cc or more.
Does turbocharging change displacement?
No. Displacement is pure geometry — the volume the pistons sweep. Forced induction changes how much air is packed into that volume, which is why a 2.0 litre turbo can outproduce a 3.5 litre naturally aspirated engine while displacing the same as before.
How is the clearance volume worked out?
The compression ratio is (swept + clearance) divided by clearance, so clearance equals swept volume divided by the ratio minus one. It is the space left above the piston at top dead centre, made up of the combustion chamber, head gasket and piston crown geometry.
Displacement reference
| Bore × stroke | Cylinders | Per cylinder | Total | Litres | Cubic inches |
|---|---|---|---|---|---|
| 71 × 84 mm | 3 | 332.6 cc | 998 cc | 1.00 L | 60.9 |
| 77 × 85.8 mm | 4 | 399.5 cc | 1598 cc | 1.60 L | 97.5 |
| 79.5 × 80.5 mm | 4 | 399.6 cc | 1598 cc | 1.60 L | 97.5 |
| 84 × 90 mm | 4 | 498.8 cc | 1995 cc | 2.00 L | 121.7 |
| 86 × 86 mm | 4 | 499.6 cc | 1998 cc | 2.00 L | 121.9 |
| 86 × 96 mm | 6 | 557.6 cc | 3346 cc | 3.35 L | 204.2 |
| 88 × 82 mm | 6 | 498.7 cc | 2992 cc | 2.99 L | 182.6 |
| 94 × 92 mm | 8 | 638.5 cc | 5108 cc | 5.11 L | 311.7 |
| 101.6 × 88.4 mm | 8 | 716.7 cc | 5733 cc | 5.73 L | 349.9 |
Computed as pi/4 x bore² x stroke x cylinders ÷ 1000, with 1 cubic inch = 16.387064 cc.