Compression Ratio Calculator
Compression Ratio Calculator: Displacement vs Clearance Volume
Compression ratio is one of the most fundamental parameters in engine design, directly influencing thermal efficiency, power output, and knock resistance. It compares the total cylinder volume when the piston is at the bottom of its stroke to the volume remaining when it's at the top.
The Formula
CR = (Vd + Vc) / Vc
Worked Example
An engine cylinder has a displacement volume of 0.5 L and a clearance volume of 0.05 L.
CR = (0.5 + 0.05) / 0.05 = 11.0:1
How to Use This Calculator
- Enter the cylinder's displacement volume (swept volume during one stroke).
- Enter the clearance volume (remaining volume at top dead center).
- Click Calculate to get the compression ratio.
Related Calculations
Higher compression ratios generally improve the Indicated Thermal Efficiency Calculator result, within knock limits set by fuel octane rating.