Ratio between blood ethyl alcohol to urine ethyl alcohol concentration is:

Urine has about 25% more water than an equal volume of blood, so its concentration of alcohol would be about 25% higher than in blood collected at the same time. In order to compare the blood and urine, a ratio of 1:1.33 is used when urine and blood are in equilibrium. Ref: The Essentials of Forensic Medicine and Toxicology by Narayan Reddy, 27th edition, Page 506.