Wallace Engine Displacement Calculator

The Wallace engine displacement calculator works out the total swept volume of an engine’s cylinders from bore, stroke, and cylinder count. You enter bore and stroke in inches (or millimeters), pick the number of cylinders, and it returns displacement in cubic inches, liters, and cubic centimeters. This page explains the formula, shows a worked example, and covers the common mistakes people make when using it.

Formula

The displacement of one cylinder is the area of the bore (a circle) multiplied by the stroke length. Multiply by the number of cylinders to get total engine displacement.

Displacement = N × (π / 4) × B² × S

• N = number of cylinders (unitless)
• B = bore (diameter of the cylinder) in inches or millimeters
• S = stroke (distance the piston travels) in the same unit as bore
• π / 4 = the constant that converts diameter squared into the area of a circle (since area = π × r² and r = B/2)

If you measure in inches, the result is in cubic inches. To convert to liters, multiply by 0.0163871 (since 1 L = 61.0237 cu in). To get cubic centimeters, multiply cubic inches by 16.3871 (or multiply liters by 1000).

Worked Example

Using the default values: bore = 4.0 in, stroke = 3.48 in, cylinders = 8 (a typical small-block V8).

1. Bore squared: 4.0² = 16.0 in²
2. Area of one bore: (π / 4) × 16.0 = 12.5664 in² (approximately)
3. Volume of one cylinder: 12.5664 × 3.48 = 43.731 in³
4. Total displacement: 43.731 × 8 = 349.85 in³
5. In liters: 349.85 × 0.0163871 = 5.733 L
6. In cc: 349.85 × 16.3871 = 5733 cc (rounded)

The calculator shows 349.85 cu in, 5.73 L, and 5733 cc for these inputs. That matches the classic “350” small-block Chevy, which is actually 349.85 cubic inches.

When to Use This Calculator

Use it whenever you need to know an engine’s displacement from its mechanical dimensions. Common situations include:

• Rebuilding an engine with a different bore or stroke (e.g., boring cylinders oversize or installing a stroker crank)
• Verifying what a “383” or “408” stroker combination actually measures
• Calculating displacement for racing class rules or insurance paperwork
• Comparing engines with different bore/stroke ratios
• Estimating the effect of a cylinder head change that alters bore (rare) or a crankshaft change that alters stroke

The calculator assumes a standard, uncompressed cylinder volume. It does not include the combustion chamber volume, head gasket thickness, piston dome/dish, or deck height. Those affect compression ratio, not displacement.

How to Read the Result

The displacement number tells you the total volume swept by all pistons from bottom dead center to top dead center. It is a fixed property of the engine geometry. A larger displacement generally means more air/fuel mixture can be drawn in per revolution, which usually produces more torque and power, but it also increases fuel consumption and emissions. Displacement alone does not tell you power output; that depends on compression ratio, cam timing, intake/exhaust flow, and engine speed.

In the U.S., displacement is often rounded to the nearest cubic inch (e.g., 350, 383, 427). In most other countries, it is rounded to the nearest tenth of a liter (e.g., 5.7 L) or to the nearest cc (e.g., 5733 cc). The calculator gives both so you can use whichever is standard for your context.

Common Mistakes and Misconceptions

• Mixing units: If you enter bore in inches and stroke in millimeters, the result is meaningless. Convert one to the other first. The calculator assumes both are in the same unit.
• Using diameter instead of radius: The formula uses bore (diameter), not radius. If you accidentally use radius, you’ll get a quarter of the true displacement.
• Forgetting the π/4 factor: Some people just multiply bore × bore × stroke × cylinders, which gives a number that is about 27% too large.
• Confusing displacement with compression ratio: Displacement is the swept volume only; compression ratio also includes the clearance volume (combustion chamber + head gasket + deck height).
• Assuming cubic inches and liters are interchangeable without conversion: 1 L is about 61 cubic inches, so a 5.7 L engine is about 350 cu in, not 5.7 × 8 = 45.6 cu in.

Bore, Stroke, and Cylinder Count Variations

Displacement scales linearly with stroke and cylinder count, but with the square of bore. That means increasing bore has a larger effect than increasing stroke by the same percentage. For example, on a V8 with a 4.0” bore and 3.48” stroke:

• Bore +0.030” (to 4.030”) gives about 355.2 cu in (+5.3 cu in)
• Stroke +0.250” (to 3.730”) gives about 375.0 cu in (+25.2 cu in)
• Both changes together give about 380.7 cu in

Typical aftermarket builds use a 4.030” bore and a 3.75” stroke to get a “383” (actually 382.7 cu in). The calculator lets you explore these combinations quickly.

Limits of the Formula

The formula is exact for the geometric swept volume of an ideal cylinder. Real engines have a slight error because the piston pin offset and connecting rod length affect the instantaneous piston position, but the total swept volume from TDC to BDC is exactly bore area × stroke, regardless of rod length. The formula does not account for:

• Piston dome or dish volume (affects compression ratio, not displacement)
• Head gasket thickness (same)
• Deck clearance (same)
• Wear or taper in the cylinder bore (negligible for displacement)

For a rebuilt engine with a bored cylinder, the actual bore is slightly larger than the stock spec. Always measure the finished bore with a micrometer, not the factory spec.

Frequently Asked Questions

What does “350” mean on an engine?

It means the engine displaces approximately 350 cubic inches. The actual displacement is often slightly less, like 349.85 cu in for the classic small-block Chevy. The number is a marketing designation, not an exact measurement.

How do I convert cubic inches to liters?

Multiply cubic inches by 0.0163871. For example, 350 cu in × 0.0163871 = 5.735 L. Conversely, multiply liters by 61.0237 to get cubic inches.

Does the calculator work for metric measurements?

Yes, if you enter bore and stroke in millimeters, the result will be in cubic millimeters. The calculator in this article uses inches, but you can convert mm to inches by dividing by 25.4 before entering. For example, a 86 mm bore is 86 / 25.4 = 3.386”.

What is the difference between displacement and engine size?

They are the same thing. Engine size is just the common term for displacement, usually expressed in liters or cubic inches.

Can I use this calculator for a rotary engine?

No. Rotary engines (Wankel) have a different method of calculating displacement, based on the swept volume of the rotor housing. The formula here applies only to reciprocating piston engines.

Why does my engine’s displacement seem larger than the factory spec?

If the engine has been bored oversize (e.g., +0.030”) or has a stroker crankshaft, the displacement increases. The calculator will show the actual displacement based on the current bore and stroke, not the original factory rating.

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in bore | Bore | in | 4.0 | 0
in stroke | Stroke | in | 3.48 | 0
in cyl | Cylinders | - | 8 | 1
out disp_ci | Displacement (cubic inches) | cu in | cyl * (pi / 4) * bore^2 * stroke | 2
out disp_l | Displacement (liters) | L | disp_ci * 0.0163871 | 2
out disp_cc | Displacement (cc) | cc | disp_ci * 16.3871 | 1