How do you calculate compression ratio?

I am building up a block and was curious on calculating the compression. Is there a formula?
y=mx+b? thanks

yang

 

http://www.bgsoflex.com/cr.html

Google: "compression ratio formula"

 

Volume at BDC : volume at TDC

 

http://www.carcraft.com/techarticles/calculate_compression_ratio/index.html

 

Wikipedia :

The ratio is calculated by the following formula:
,
where
b = cylinder bore (diameter)
s = piston stroke length
Vc = volume of the combustion chamber (including head gasket). This is the minimum volume of the space into which the fuel and air is compressed, prior to ignition. Because of the complex shape of this space, it usually is measured directly rather than calculated.

• Due to pinging (detonation), the CR in a gasoline/petrol powered engine will usually not be much higher than 10:1, although some production automotive engines built for high-performance from 1955-1972 had compression ratios as high as 12.5:1, which could run safely on the high-octane leaded gasoline then available. A technique used by Audi to prevent the onset of knock is the high "swirl" engine that forces the intake charge to adopt a very fast circular rotation in the cylinder during compression that provides quicker and more complete combustion. Recently, with the addition of variable valve timing and knock sensors to delay ignition timing, one worldwide manufacturer is building 10.8 CR gasoline engines that use 87 MON (octane rating) fuel.
• Motocycle racing engines can use compression ratios as high as 14:1, and it is not uncommon to find motorcycles with compression ratios above 12.0:1 designed for 86 or 87 octane fuel.
• In engines running exclusively on LPG or CNG, the CR may be higher, due to the higher octane rating of these fuels.
• Racing engines burning methanol and ethanol often exceed a CR of 15:1.
• In engines with a 'ping' or 'knock' sensor and an electronic control unit, the CR can be as high as 13:1 (2005 BMW K1200S)
• In a turbocharged or supercharged gasoline engine, the CR is customarily built at 9:1 or lower.
• In an auto-ignition diesel engine, the CR will customarily exceed 14:1. Ratios over 22:1 are common
• In 1981, Jaguar released a cylinder head that allowed up to 14:1 compression; but settled for 12.5:1 in production cars. The cylinder head design was known as the "may fireball" head.

 

thanks guys, its more complicated than I thought lol

 

What did you think it was? Seems simple to me - just the ratio of max cylinder volume to minimum volume

 

I do air compressor compression ratio's quite a bit a school (PSI+14.7)/14.7 = CR