Compression Ratio Calculator

When building a performance Classic Mini engine one of the most important figures to determine is the compression ratio. Using the Classic Mini DIY Compression Ratio Calculator below, you can determine the ideal compression for your new engine build.

+20 - 71.10mm
1275cc - 81.28mm
1275 - 3.4cc
None (0cc)

Piston Dish size (cc)

Cylinder Head Chamber Volume (cc)

Piston Deck Height (thou)


Please note the above figures are approximate values. Before purchasing parts and building your engine we recommend doublechecking your calculations multiple times using more than one source. The mathematical equations used in this tool can be found here: Equation Source Code

Alternate Source: Calver Compression Ratio, JE Pistons Compression Ratio

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Classic Mini DIY by Cole Gentry .

Classic Mini DIY toolbox is a passion project aligned with the Classic Mini DIY youtube channel. This is a completely free resource built to keep the Classic Mini technical knowledgebase alive for years to come. Regularly updated and crowd sourced data made to help Classic Mini owners all over the world.

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