Calculate the compression or expansion ratio of an internal combustion engine cylinder.
Cylinder Dimensions
Ratio Results
Enter swept and clearance volumes
About this calculator
Quick Reference
VcSwept cylinder volume
VhClearance (chamber) volume
TDCTop Dead Center (highest piston position)
BDCBottom Dead Center (lowest piston position)
Overview
The compression ratio is a fundamental specification for internal combustion engines. It compares the total volume of the cylinder when the piston is at the bottom of its stroke to the volume when it is at the top.
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Pro Tips
Formula: Ratio = (Vc + Vh) / Vh.
Swept volume (Vc) is the volume displaced by the piston travel.
Clearance volume (Vh) is the volume remaining above the piston at Top Dead Center.
Higher ratios generally lead to better thermal efficiency but require higher octane fuel.
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Fun Facts
"Modern gasoline engines typically have ratios between 8:1 and 12:1."
"Diesel engines have much higher ratios, often between 14:1 and 23:1, to ignite fuel via heat of compression."
"The Atkinson cycle engine used in hybrids effectively has a higher expansion ratio than compression ratio for better efficiency."
