Engine Compression Ratio Calculator
Calculate engine compression ratio from swept volume and clearance volume. See recommended fuel octane for your ratio.
Compression Ratio
11.0:1
Recommended Octane
93 (Premium)
๐ก CR = (Swept + Clearance) รท Clearance = (500 + 50) รท 50 = 11.0:1
๐ก How to Use the Engine Compression Ratio Calculator
How to Calculate Compression Ratio
Compression ratio (CR) is the ratio of the cylinder's total volume (when the piston is at bottom dead center) to the clearance volume (when the piston is at top dead center). Higher compression extracts more energy from each combustion event, increasing power and efficiency โ but requires higher-octane fuel to prevent detonation.
CR = (Swept Volume + Clearance Volume) รท Clearance Volume
Example: 500cc swept + 50cc clearance = (500 + 50) รท 50 = 11.0:1
Compression Ratio & Fuel Requirements
| CR | Minimum Octane | Typical Application |
|---|---|---|
| 8.0:1 โ 9.5:1 | 87 (Regular) | Economy cars, trucks |
| 9.5:1 โ 10.5:1 | 91 (Mid-Grade) | Performance sedans |
| 10.5:1 โ 12.5:1 | 93 (Premium) | Sports cars, performance |
| 12.5:1+ | 100+ (Race Fuel) | Race engines |