I believe that in English the pattern to use is "x by y". How would you say about size of your bed, for example?
In Russian it's "на". Add more "на"s if there are more than two figures:
2,5x3,0x1,0 м = два с половиной на три на метр

"на" is also used with probabilities:
Скачать музыка 50х50 - ТО
50:50 = пятьдесят на пятьдесят

But:
1:3 = один к трём

Even more interesting:
1:1000000
A) один на миллион
B) один к миллиону

both are possible if you mean relation, and only A possible if you mean dimensions.