Bore X Stroke Calculator

The Bore x Stroke Calculator is an essential tool for engine builders, mechanics, performance tuners, and automotive enthusiasts. It helps determine the engine displacement—a critical specification that affects power, torque, fuel efficiency, and overall performance of an internal combustion engine.

Bore × Stroke Calculator

📘 What Is Bore and Stroke?

  • Bore is the diameter of each cylinder in the engine.
  • Stroke is the distance the piston travels from the top to the bottom of the cylinder.
  • The combination of bore and stroke determines the engine displacement—the total volume swept by all pistons inside the cylinders.

Displacement is typically expressed in:

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

🎯 Importance of Calculating Bore x Stroke

  1. Performance Insight: Engine displacement directly impacts power and torque.
  2. Tuning & Modding: Knowing this helps in choosing cams, turbos, or injectors.
  3. Racing Compliance: Displacement determines the class and regulations in motorsports.
  4. Engine Swap Validations: Helps match engine specs to vehicle requirements.

🛠️ How to Use the Bore x Stroke Calculator

Using this calculator is easy. Just enter the values for:

  • Bore (in mm or inches)
  • Stroke (in mm or inches)
  • Number of Cylinders

Step-by-Step Guide:

  1. Input the bore size of the engine cylinder.
  2. Enter the stroke length the piston travels.
  3. Specify the number of cylinders in the engine.
  4. Click “Calculate” to instantly get the engine displacement in cc, L, or cubic inches.

🧮 Bore x Stroke Formula

The basic formula to calculate engine displacement is:

Displacement (per cylinder) = π × (Bore ÷ 2)² × Stroke
Total Displacement = Displacement per cylinder × Number of cylinders

Where:

  • Bore and Stroke must be in the same unit (usually millimeters or inches).
  • π (pi) is approximately 3.1416

For Metric Units (mm):

Convert the result from cubic millimeters to cc by dividing by 1000.

📌 Example Calculation

Given:

  • Bore = 86 mm
  • Stroke = 86 mm
  • Cylinders = 4

Step 1: Calculate Volume per Cylinder

= π × (86 / 2)² × 86
= 3.1416 × 43² × 86
= 3.1416 × 1849 × 86
≈ 499,759 mm³ per cylinder

Step 2: Total Displacement

= 499,759 × 4 = 1,999,036 mm³

Step 3: Convert to Cubic Centimeters

= 1,999,036 ÷ 1000 ≈ 1999 cc or 2.0 L

🔄 Bore x Stroke Ratio

  • The Bore/Stroke ratio indicates whether an engine is oversquare, square, or undersquare:
    • Oversquare (Bore > Stroke): High-revving engines (e.g., motorcycles, sports cars)
    • Square (Bore = Stroke): Balanced performance
    • Undersquare (Stroke > Bore): High torque at low RPM (e.g., diesel engines)

Understanding this ratio helps in predicting the engine’s behavior.

🚗 Applications of Bore x Stroke Calculations

  • Engine design and testing
  • Performance upgrades and custom builds
  • Cylinder head matching
  • Racing regulation compliance
  • Choosing turbochargers and camshaft profiles

💡 Additional Tips

  • Always use accurate measurements for bore and stroke.
  • Convert inches to mm (1 inch = 25.4 mm) when required.
  • When working with cubic inches, multiply cubic centimeters by 0.061024.

📉 Common Mistakes to Avoid

  • Mixing units (e.g., bore in mm, stroke in inches)
  • Using nominal rather than actual measurements
  • Forgetting to multiply by the number of cylinders

🔄 Unit Conversions

  • 1 cc = 0.001 L
  • 1 cc = 0.061024 ci
  • 1 inch = 25.4 mm
  • To convert ci to L: ci × 0.016387

🤔 Frequently Asked Questions (FAQs)

1. What is engine displacement?

Engine displacement is the total volume of all cylinders in an engine, usually measured in cc, L, or ci.

2. Why is bore and stroke important?

It defines engine size and influences power, torque, and RPM behavior.

3. Can I use this calculator for motorcycle engines?

Yes, it works for any piston-driven internal combustion engine.

4. What’s a good bore/stroke ratio?

Depends on your goals: oversquare for RPM and undersquare for torque.

5. How accurate is this calculator?

Extremely accurate when using precise input values.

6. Can I use inches instead of mm?

Yes, just ensure all values are in the same unit.

7. What’s the formula for cubic inches?

Displacement (ci) = (π × Bore² × Stroke × Cylinders) ÷ 4 × 0.061

8. Does stroke affect torque?

Yes, longer stroke engines typically produce more torque.

9. Does bore affect RPM?

Yes, larger bore engines usually support higher RPMs.

10. Is displacement the same as engine size?

Yes, it’s often used interchangeably with engine size.

11. Can I calculate displacement for V8 engines?

Yes, just input 8 as the number of cylinders.

12. What unit should I choose for bore/stroke?

Preferably mm for precision, but inches also work.

13. Why do two engines have the same displacement but different power?

Other factors like air/fuel ratio, compression, and tuning play a role.

14. Can I calculate displacement for a single cylinder?

Yes, input 1 for the number of cylinders.

15. What’s the purpose of bore honing?

To smooth and resize the cylinder bore for better piston movement.

16. What is a stroked engine?

An engine modified to have a longer stroke for increased displacement.

17. How do I measure bore and stroke manually?

Use a caliper or micrometer for bore, and dial indicator for stroke.

18. What’s the displacement of a 5.7L engine in ci?

5.7L × 61.024 = ~348 ci

19. What is a square engine?

An engine where the bore equals the stroke.

20. Does bigger displacement always mean more power?

Generally, yes, but tuning and design affect actual output.

🧰 Summary

The Bore x Stroke Calculator is a valuable tool for calculating engine displacement with speed and accuracy. By inputting bore, stroke, and cylinder values, users can instantly determine engine size in cc, L, or ci. Whether you’re a gearhead or a professional, this calculator supports better decisions in engine design, performance optimization, and compliance.