Bore X Stroke Calculator

What Is Bore in an Engine?

Bore is the diameter of the cylinder inside the engine block.

In simple terms, it is how wide the cylinder is. A larger bore means:

• Bigger piston diameter
• More air and fuel can enter the cylinder
• Potential for more power at high RPM

Bore is measured in:

• Inches (common in US engines)
• Millimeters (common in metric engines)

For example:

• 4.000 inches bore
• 101.6 mm bore

Both represent the same measurement.

What Is Stroke?

Stroke is the distance the piston travels from:

• Top Dead Center (TDC)
  to
• Bottom Dead Center (BDC)

This distance is controlled by the crankshaft.

A longer stroke means:

• The piston travels farther
• More leverage on the crankshaft
• Stronger low-RPM torque

Stroke is also measured in inches or millimeters.

Example:

• 3.480 inches stroke
• 88.4 mm stroke

What Is Engine Displacement?

Engine displacement is the total volume of all cylinders combined.

It tells you the size of the engine.

Common displacement units:

• Cubic centimeters (cc)
• Liters (L)
• Cubic inches (CID)

For example:

• 2.0L engine
• 350 cubic inch engine
• 5.7L V8

All are displacement values.

The Engine Displacement Formula

The formula used in a bore x stroke calculator is:

Volume per cylinder = π × (radius²) × stroke

Then:

Total displacement = Volume per cylinder × number of cylinders

Where:

• Radius = Bore ÷ 2
• π (pi) ≈ 3.1416

The calculator automatically:

• Converts inches to millimeters when needed
• Calculates cc
• Converts to liters
• Converts to cubic inches

So you do not need to do manual math.

What Is Bore/Stroke Ratio?

The bore/stroke ratio is:

Bore ÷ Stroke

This ratio determines engine geometry.

It tells you how the engine is designed to perform.

There are three main types:

1. Oversquare Engine (Short Stroke)

Ratio: Greater than 1.05

Bore is larger than stroke.

Example:

• 4.125″ bore
• 3.480″ stroke

Characteristics:

• Higher RPM capability
• Larger valves
• Better airflow
• More top-end horsepower
• Lower piston speed

Common in:

• Sports cars
• Racing engines
• High-performance builds

This design helps engines breathe better at high speed.

2. Undersquare Engine (Long Stroke)

Ratio: Less than 0.95

Stroke is longer than bore.

Example:

• 3.500″ bore
• 4.000″ stroke

Characteristics:

• Strong low-end torque
• Better pulling power
• Lower RPM redline
• Higher piston speed

Common in:

• Trucks
• SUVs
• Diesel engines
• Economy cars

This design gives strong torque at lower RPM.

3. Square Engine (Balanced Design)

Ratio: Between 0.95 and 1.05

Bore and stroke are nearly equal.

Example:

• 86mm bore
• 86mm stroke

Characteristics:

• Balanced torque and horsepower
• Good fuel efficiency
• Smooth operation
• Versatile performance

Many modern engines use this design.

What the Bore X Stroke Calculator Shows

The calculator you provided performs several key calculations:

1. Total Engine Displacement

Displayed in:

• Liters
• Cubic inches
• Cubic centimeters

2. Displacement Per Cylinder

Useful for engine builders who want precise tuning data.

3. Bore/Stroke Ratio

Displayed as:
Example: 1.18:1

4. Engine Geometry Type

• Oversquare
• Undersquare
• Square

5. Visual Comparison Bar

It visually shows whether bore or stroke dominates.

6. Builder Analysis

It explains what your engine design means in real performance terms.

This is especially helpful for beginners who do not yet understand engine geometry.

Example Calculation

Let’s say you enter:

• Bore: 4.000 inches
• Stroke: 3.480 inches
• Cylinders: 8

The calculator will show approximately:

• 5.7 liters
• 350 cubic inches
• Oversquare design

That is a classic V8 size used in many American performance engines.

Why Bore and Stroke Matter

Bore and stroke affect:

• Horsepower potential
• Torque curve
• RPM limits
• Piston speed
• Engine efficiency
• Combustion characteristics

Even small changes can change engine behavior.

For example:

Increasing stroke increases torque.
Increasing bore increases high-RPM breathing.

That is why engine builders carefully choose bore and stroke combinations.

When Should You Use a Bore X Stroke Calculator?

You should use it when:

• Designing a custom engine build
• Swapping crankshafts
• Changing piston sizes
• Boring out cylinders
• Comparing engine configurations
• Planning a stroker build

It saves time and prevents costly miscalculations.

Metric vs Inches

The calculator supports:

• Inches (US standard)
• Millimeters (metric)

Internally, it converts everything correctly before calculating volume. This prevents unit errors.

Always double-check your measurement units before calculating.

Common Mistakes to Avoid

1. Mixing metric and inch measurements
2. Entering zero or negative values
3. Forgetting to update cylinder count
4. Assuming bigger displacement always means more power

Power depends on many factors beyond displacement.