Compression Ratio Calculator

About the Compression Ratio Calculator

The Compression Ratio Calculator determines the static compression ratio of an internal combustion engine, a critical parameter for performance and efficiency.

Calculation Method: Computes the ratio of the total volume (swept volume plus clearance volume) to the clearance volume at top dead center, using bore, stroke, and various chamber volumes.

Use this tool for engine building, tuning, or designing high-performance engines in automotive applications.

• Features:
  • Inputs: Bore, stroke, combustion chamber volume, piston dome volume, head gasket volume, and unit (metric or imperial).
  • Keypad includes digits (0–9), decimal point (.), and negative sign (-) for numerical input.
  • Displays compression ratio with calculation steps in LaTeX format using MathJax.
  • Clear, backspace, and copy functionality for results.
  • Share or embed the calculator.
• Practical Applications: Useful for automotive engineers, mechanics, tuners, or enthusiasts optimizing engine performance or selecting fuel types.
• How to Use:
  • Select unit (metric for cm³, imperial for in³).
  • Enter bore, stroke, combustion chamber volume, piston dome volume (negative for dished pistons), and head gasket volume.
  • Use the keypad to input digits, decimal points, or negative signs.
  • Click "Calculate" to view the compression ratio.
  • Use "Clear" to reset or "⌫" to delete the last character.
  • Copy results or share/embed the calculator.
• Helpful Tips:
  • All inputs except piston dome volume must be positive; piston dome volume is negative for dished pistons, positive for domed pistons, or zero for flat-top pistons.
  • Typical bore and stroke: 80–100 mm (3–4 inches) for passenger cars.
  • Combustion chamber volume: 30–60 cm³ (1.8–3.7 in³) for typical engines.
  • Head gasket volume: 5–15 cm³ (0.3–0.9 in³), depending on thickness and bore.
  • Compression ratios: 8:1–10:1 for street engines, 10:1–12:1 for performance, 12:1+ for racing (requires high-octane fuel).
• Calculation Details:
  • Swept Volume: \(\text{Swept Volume} = \frac{\pi}{4} \times \text{Bore}^2 \times \text{Stroke}\).
  • Clearance Volume: \(\text{Clearance Volume} = \text{Combustion Chamber Volume} + \text{Piston Dome Volume} + \text{Head Gasket Volume}\).
  • Compression Ratio: \(\text{CR} = \frac{\text{Swept Volume} + \text{Clearance Volume}}{\text{Clearance Volume}}\).
  • Metric: Volumes in cm³ (bore and stroke in cm); Imperial: Volumes in in³ (bore and stroke in inches).
  • Conversion: 1 cm = 10 mm, 1 cm³ = 0.0610237 in³.
• Examples:
  • Example 1:
    • Inputs: Unit = Metric, Bore = 86 mm, Stroke = 86 mm, Combustion Chamber Volume = 50 cm³, Piston Dome Volume = 0 cm³, Head Gasket Volume = 10 cm³
    • Calculation:
      • Convert bore and stroke to cm: \(86 \div 10 = 8.6 \, \text{cm}\)
      • Swept Volume: \(\frac{\pi}{4} \times 8.6^2 \times 8.6 = 500.14 \, \text{cm}^3\)
      • Clearance Volume: \(50 + 0 + 10 = 60 \, \text{cm}^3\)
      • Compression Ratio: \(\frac{500.14 + 60}{60} = 9.34\)
      • Round to two decimal places: 9.34
    • Result: Compression Ratio = 9.34:1
  • Example 2:
    • Inputs: Unit = Imperial, Bore = 4 inches, Stroke = 3.5 inches, Combustion Chamber Volume = 3 in³, Piston Dome Volume = -0.5 in³, Head Gasket Volume = 0.5 in³
    • Calculation:
      • Swept Volume: \(\frac{\pi}{4} \times 4^2 \times 3.5 = 43.98 \, \text{in}^3\)
      • Clearance Volume: \(3 + (-0.5) + 0.5 = 3 \, \text{in}^3\)
      • Compression Ratio: \(\frac{43.98 + 3}{3} = 15.66\)
      • Round to two decimal places: 15.66
    • Result: Compression Ratio = 15.66:1

Optimize engine performance with this interactive Compression Ratio Calculator. Share or embed it on your site!