The ratios for CPR are also very important and luckily they are easy to remember. When doing one man CPR the ratio is 30 chest compressions to 2 breaths. That 30 to 2 ratio is the same when doing CPR on an Adult or Child. The only time when it changes just a little is when you do CPR on an infant; the ration then becomes 30 chest compressions to 2 puffs. 2 Puffs means you only fill your cheeks up with air when breathing for an infant.