Enter the cylinder bore diameter, stroke length, and the minimum clearance at end of the compression stroke. The calculator will evaluate and display the compression ration of the engine.

## Compression Ratio Formula

The following formula can be used to calculate the compression ratio of an engine.

CR = [ (PI/4*b^2*s) + Vc ]/Vc

- Where CR is the compression ratio
- b is the cylinder bore diameter
- s is the stroke length
- Vs is the minimum clearance at the end of the compression stroke

How to calculate compression ratio

**First, measure the bore cylinder diameter**This should be the inner diameter of the cylinder, not the outer diameter.

**Next, measure the stroke length**Measure the stroke length of the cylinder.

**Next, determine the minimum clearance**It’s important that the minimum clearance is the clearance when the compression stroke is at it’s highest point.

**Calculate the compression ratio**Enter the information from steps 1-3 into the equation above to calculate the compression ratio.

## FAQ

**What is a compression ratio?**

A compression ratio is a fundamental specification in combustion engine design that measure the ratio of the total working volume of a piston and it’s compression volume.

**What is a good compression ratio?**

The higher the compression ratio the better the performance of a piston. The more compression the fuel undergoes, the more pressure it sees, and the higher the thermal efficiency of the engine.

**What is thermal efficiency of an engine?**

Thermal efficiency is the total mechanical energy that can be extracted from a set amount of fuel.

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