I've just found this online calculator, it seems to work pretty well. It doesn't list every possible piston size, combination and parameter, but it is enough to get a general idea of how it all works.
http://www.podifold.com/compression.html

The nominal cylinder head volumes can be found here.
http://www.minimania.com/Cylinder_head_ ... ing_number

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I remember when Apple iPhones were brand new, someones first thought when the dazzling arrays of APP possibilities was placed before them decided to make a compression calculator

God bless their clever noodles

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

CV + SV divided by CV

CV being combusted volume
SV being Swept Volume

CC tools needed are a Burette, a sheet of perspex/plastic big enough to cover the cyl head chamber & bore,,, smear a thing smidge of grease on the surface, squish the plastic down firm & fill with burette full of kero/metho etc

make sure you fit a spark plug & valves into the cyl head

make sure you run a slight bit of grease around the bore & bring piston up to TDC (top dead center)

fill with burette,

add the chamber vol To the (approx) 3.5cc in the head gasket plus the vol above the piston at TDC , all together
& that`s your CV

divide your engine size by 4,,, giving one cyl swept volume

divide the SV by the CV & add one
the answer is your compression ratio

easy-peasy

if you want examples then list what you have & i`ll do it for you here so you all can see how easy it really is
it may sound like there`s lots in it & it`s all too confusing but it`s not really
it`s a piece of pi$$

i do it to every single engine we build to make sure we are spot-on
too much & you`ll ping

too little & it`ll be a bit doe-y

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

jack up the front of the car so that the spark plug holes are horizontal (spark plugs are vertical) pick a cylinder that has both valves closed. Fill the cylinder with light oil using a big syringe

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did I tell you that I won a trophy?