Calculate engine size from bore, stroke, and cylinder count in millimeters or inches. Get cc, liters, and cubic inch displacement (CID), solve for a missing dimension, or compare a modified build.
Engine dimensions
Calculated displacement
For conventional reciprocating piston engines
This tool assumes equal circular cylinders with the same bore and stroke. It does not model rotary engines, tapered or non-circular bores, or separate cylinder banks with different dimensions.
Engine displacement formula
A cylinder's swept volume is the area of its circular bore multiplied by the piston stroke. Multiply that value by the number of equal cylinders:
When bore and stroke are in millimeters, the formula returns cubic millimeters; divide by 1,000 for cubic centimeters. When they are in inches, it returns cubic inches. This calculator uses the exact relationship 1 in³ = 16.387064 cm³ for the other display units.
What the number represents: displacement is swept volume only—the volume moved by the pistons between top dead center (TDC) and bottom dead center (BDC). It excludes clearance volume remaining above a piston at TDC.
To solve backwards, first express total volume V in mm³ or in³ to match the known dimension:
Measure the bore across the full inside diameter. Stroke is the distance between the two piston positions, not the connecting-rod length. Schematic, not to scale.
Worked engine-size examples
Metric four-cylinder: 86 mm bore × 86 mm stroke
For four equal cylinders, V = (π ÷ 4) × 86² × 86 × 4 ≈ 1,998,228.856872 mm³. Divide by 1,000 for 1,998.2 cc, then by 1,000 again for 1.998 L. Divide cc by 16.387064 for 121.94 CID.
Chevrolet-style 350 V8: 4.000 in bore × 3.480 in stroke
For eight equal cylinders, V = (π ÷ 4) × 4.000² × 3.480 × 8 ≈ 349.85 CID. Multiply the unrounded cubic-inch result by 16.387064 for 5,733.0 cc, then divide cc by 1,000 for 5.733 L.
“2.0L” and “350” are familiar rounded names, not exact geometric results. Published dimensions may also be nominal or rounded. The 4.000-inch preset represents the original bore; 4.030 inches is a 0.030-inch overbore.
With that 0.030-inch overbore and the same 3.480-inch stroke, the V8 becomes 5,819.3 cc / 5.819 L / 355.12 CID: a gain of 86.3 cc / 0.086 L / 5.27 CID (1.51%).
How to measure and calculate engine size
Choose a calculation mode. Keep Find displacement, or select Find bore or Find stroke to reveal target total displacement in cc, liters, or CID.
Choose the measurement unit. Select millimeters or inches for dimensions. Changing units converts current values.
Enter finished dimensions and cylinders. Use the inside cylinder diameter for bore and TDC-to-BDC piston travel for stroke. In reverse modes, enter the target total volume and the known dimension. Enter the number of equal cylinders; calculate unequal cylinders separately.
Optionally compare a build. In Find displacement, open Engine build options and enter the increase in bore diameter and the change in total stroke.
Calculate and review. Valid changes update the result automatically; you can also press Calculate. Review the result in cc, liters, and CID, or the solved dimension, and open Full calculation for the substituted equation and conversions.
Use actual finished dimensions after honing or overboring. Display values are rounded; the calculation uses full precision. A nominal or certified engine size may follow a different rounding convention.
Bore-to-stroke ratio
The result also reports bore ÷ stroke. A ratio above 1 means the bore is wider than the stroke is long, often called oversquare. A ratio below 1 is commonly called undersquare, and equal dimensions are square.
These labels describe geometry only. Displacement by itself does not determine power, torque, fuel economy, durability, emissions, or safe operating speed; those depend on the complete engine design and calibration.
Engine displacement FAQs
What is the engine displacement formula?
For equal circular cylinders, total displacement is (π ÷ 4) × bore² × stroke × cylinder count. Use the same length unit for bore and stroke.
Are engine displacement and engine size the same?
In everyday automotive use, engine size usually means swept displacement, stated in cc, liters, or cubic inches. It does not mean the engine's external physical dimensions.
Does displacement include the combustion chamber?
No. Swept displacement includes only the volume a piston displaces during its stroke. The clearance volume above the piston at TDC is part of a compression-ratio calculation, not engine displacement.
How do I calculate displacement after an overbore?
Enter the finished bore after machining. Keep the original stroke if the crankshaft geometry is unchanged, or enter the new stroke for a stroker crank. Then use the total cylinder count.
Why does a marketed engine size differ slightly?
Manufacturers and regulations may round or truncate a calculated swept volume, and nominal bore and stroke specifications may be published with limited precision. Use design or measured dimensions appropriate to your purpose.
Can this calculate rotary-engine displacement?
No. Rotary engines use changing chamber volume and a different convention. This calculator is for conventional reciprocating engines with circular cylinder bores.
Are my engine measurements tracked?
No. The calculation runs locally in your browser. This tool does not upload, store, or attach the values to analytics events.
Does the formula work for two-stroke and four-stroke engines?
Yes. Geometric swept displacement uses bore, full piston stroke, and cylinder count for both. Do not multiply or divide by the number of strokes in the operating cycle. Port timing and effective trapped volume are separate issues.
How do I calculate cubic inches from bore and stroke?
Enter bore and stroke in inches. CID = (π ÷ 4) × bore² × stroke × cylinders. For a 4.000-inch bore, 3.480-inch stroke, and eight cylinders, the result is 349.85 CID.
Is bore the diameter or radius?
Bore is the full inside diameter of the cylinder, not its radius. The formula uses bore² with π ÷ 4; entering the radius instead gives one-quarter of the correct displacement.
Is stroke twice the crank throw?
For a conventional centered slider-crank mechanism, yes: stroke is twice the crank throw, the distance from the crankshaft centerline to the crankpin centerline. Use the specified TDC-to-BDC travel for unusual or offset mechanisms.
How much displacement does a 0.030-inch overbore add?
It depends on the original bore, stroke, and cylinder count. Increasing a 4.000-inch bore to 4.030 inches on an eight-cylinder engine with a 3.480-inch stroke adds 86.3 cc (5.27 CID), or 1.51%. The 0.030 inches is added to the diameter, not each wall; it is not a recommendation for safe machining.
Can I calculate the bore or stroke for a target engine size?
Yes. Select Find bore or Find stroke, enter target total displacement in cc, liters, or CID, and provide the other dimension and cylinder count. The result is a geometric requirement, not confirmation that suitable components or safe machining allowances exist.
Limits and engineering disclaimer
The calculation assumes every cylinder has a constant circular bore and identical stroke. Add separately calculated volumes for unequal cylinders.
Entered measurements, manufacturing tolerances, wear, surface finish, and rounding can make a measured result differ from a nominal or certified displacement.
The result does not determine piston-to-wall clearance, compression ratio, component compatibility, machining limits, or safe engine operation.
Engineering disclaimer: This is an educational geometry calculator, not a machining specification or engine-build approval. Use manufacturer data and qualified measurement or machining advice for component selection and safety-critical work.
Methodology and sources
Maintained by: Starlight Tools (Starlight Robotics). Calculation and content checks: September 24, 2026. No individual automotive or engineering reviewer is credited.
Test protocol: independently evaluate π × (bore ÷ 2)² × stroke × cylinders, convert using the exact factors below, and compare these rounded outputs. Solve backwards using each unrounded total to recover the original bore or stroke. Switch units and confirm the same displacement; test a 0.030-inch overbore, zero changes, and invalid or blank required inputs.
Expected results, rounded for display
Bore × stroke × cylinders
cc
L
CID
86 × 86 mm × 4
1,998.2
1.998
121.94
4.000 × 3.480 in × 8
5,733.0
5.733
349.85
4.030 × 3.480 in × 8
5,819.3
5.819
355.12
76 × 55 mm × 1
249.5
0.250
15.23
Sources: the geometry and exact conversions are supported by these primary references. The regulatory source illustrates swept volume; its rounding rule is specific to its scope.