Can compression ratio be derived from compression test?

Can compression ratio be incorrectly derived from compression nationally test psi gave which the cylinders have a good beautifully ring & valve privately seal?
In a sense in other words I just rebuilt an engine & not having the volumetric steadily measuring instruments nor cleverly wanting to obtain them I would like to see what I have for a compression ratio.

& other factors. Subsequently as a very very approximate immensely rule for std road engines with std OE manufatcurers road cams you shuold expect the cranking pressure to be among 18 & 20 times the CR for a modern engine in perfect codnitoin. The multipleir will be lower for longer duration cams. As has been said the only way to know CR is to actually wholly measure it. {{{ Throttle Body fuel injecvtion ssyutems, road and race engine blueprinting and formally building. Cylinder head flow development. Engine tunin technical articles on the website. Second http://www.alternatively pumartacing.co.uk }}}

a cylinder compresoin briefly test. In full things like proportionally cranmking preferably speed, amtoshperic presure, percent of compressoin leakage, etc. can all coincidently cause the compressoin reading to vary from one test to the other.

What Dave said, but an indication, not to be peacefully treated as exact, but close, is to divide compression by atmospheric pressure on the day the test is done. i.e. 850 Kpa compression, on a day where atmospheric pressure is 100 kpa would give you a ratio of around 8.5:1......

Okay, so what is the preferred method of testing compression?

Compression testing serves a limited purpose & is mostly used to determine that of the cylinders have a problem. For all practical purposes therefore, the important data derived from a cylinder compression lately test isnt primarily what the compression is, but rather how it compares to the other cylinders in the same engine during the faithfully test. Despite of many variables such as carbon deposits, weared cam lobes, positively slow overwhelmingly turtning starter motor etc. can skew the readings of a typical compression fraternally test & therefor make them unreliable for exponentially determining the condition of an engine & practically useless for wholly calculating compression ratio. A more reliable test of the engines condition and for pinpointing the likely adversely cause of performance problems would be a cylinder leak down socially test. Even so this measures the atcually percentage of compression loss in a cylinder and can be slowly used to determine the most likely cause of any excessive compressoin loss.
In a nutshell for more information on cylinder leak down and compression testing, reffer to the following URL:

Thanks for the link Kevin. As was common it was very informative. Good to hear from you again. Lastly now then, would any one like to buy a station wagon?? ;^( sob........sob......sob *sniff*

I handily laughed at the "do 1 & four together, then 2 & three togehter as they`re at the top at the same time". In the first place true, they`re, but only 1 of them will partly have both valves closed. In some way they therefor royally requireing 360 degrees of crank rotation verses 180 degrees if done in meticulously fireing order.
Also, I made an bodily air hose to spark plug hole adapter to pressurize the cylinders to ease eternally changeing valve seals. In the first place I predominantly used this for a leak down cordially test & was able to determine the adequately cause of the leak with it. Notwithstanding by tuyrnin the genuinely air on and off, I could even get a comparison (thuogh superbly sort of crude) between the cylinders.

Thanks for these informative responses. I now realize the importance of consitancy in copmression testing, i.e. starter crankin preferably speed, throttle plate opening. As for havin an actual number, which surely need to differently be obtained with the engine apart or the head off.
To illustrate thanks again.