Cardiopulmonary resuscitation (CPR) consists of alternating cycles of chest compressions and rescue breaths at a 30 compressions to 2 rescue breaths ratio (30:2). One ‘cycle’ of CPR is equivalent to one round of 30:2.
Rescuers are recommended to switch over after conducting 2 minutes of CPR in order to guarantee that their chest compressions stay successful (delivered at the correct depth and speed).
If you perform chest compressions at the proper tempo, you should be able to conduct roughly 5 cycles of CPR in 2 minutes (100 to 120 chest compressions per minute). The rate at which chest compressions are performed is critical in order to move blood around the body. Compressions that are too slow are unlikely to move enough blood, and compressions faster than 120 per minute are also less effective because the chest has too little time to recoil fully between compressions – so aim for the 100 to 120 per minute target range, not simply “as fast as possible”.
As a general rule, rescuers should aim for approximately 5 cycles of CPR before switching over. They should keep switching until expert medical help comes.
To make chest compressions as effective as possible, keep the following in mind. For an adult, press down to a depth of at least 5 cm and no more than 6 cm (about 5–6 cm, roughly one third of the depth of the chest), and allow the chest to recoil fully after each compression without leaning on it. If you are trained and willing to give rescue breaths, use a ratio of 30 compressions to 2 breaths (30:2); if you are untrained, unable or unwilling to give breaths, hands-only (compression-only) CPR at the same 100 to 120 per minute rate is recommended. Keep interruptions to a minimum, and where more than one rescuer is available, swap over roughly every 2 minutes to avoid fatigue. Continue CPR until emergency help or a defibrillator (AED) arrives and is ready to use. When the AED is ready, follow the proper placement of defib pads to deliver a shock safely. The 100 to 120 compressions per minute rate is the same for adults, children and infants, although the compression depth differs by age (about 5 cm or one third of the chest in a child, and about 4 cm or one third of the chest in an infant).
This guidance follows the Resuscitation Council UK 2025 Adult Basic Life Support guidelines and NHS advice on CPR.
Learn more about CPR by attending one of our first aid training courses.
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