A simple javascript calculator that I've found helpful.

I don't remember where I swiped this one from, but whoever you are, thanks.

Engine Item	MM	Inches	Measurement
Engine Bore
Engine Stroke
Deck Height * Add "-" for piston above deck surface
Total Combustion Chamber Volume CC's
Your Compression Ratio is
Number of cylinders			1 2 3 4 5 6 8 10 12
Your Displacement is :

Solve for which variable ?

mm to inch conversion
mm	inch	fraction