The Rate and Depth in the Guidelines
MedlinePlus, whose CPR page cites the 2025 American Heart Association guidelines, gives these figures for an adult or a child after puberty:
- Rate: 100 to 120 compressions per minute.
- Depth: about 2 inches (5 centimeters).
- Let the chest rise completely after each compression.
- Cycles of 30 compressions and 2 rescue breaths, with pauses for the breaths under 10 seconds.
- With two or more rescuers, switch every 2 minutes, or after about 5 cycles, to prevent fatigue.
St John Ambulance gives the same rate and a depth of about 5 to 6 centimeters. It says that if you are unable or unwilling to give rescue breaths, you should give continuous chest compressions.
Both start with the emergency call: 911 in the US, 999 or 112 in the UK. St John Ambulance notes that the ambulance call handler will tell you what to do and help you push at the right speed.
What the Tempo Means in Seconds
At 100 BPM there is one compression every 0.6 seconds, and at 120 BPM one every 0.5 seconds. A set of 30 compressions takes 15 to 18 seconds at that pace, or about 16 seconds at 110 BPM.
MedlinePlus suggests counting the 30 compressions out loud. The count keeps track of the set, and the click keeps the speed.
How to Practice With the Metronome
Open the metronome, tap the tempo number, type 110, and tap Start. Any tempo from 100 to 120 BPM is within the guideline rate. It runs in the browser and needs no microphone.
Do one compression per click on a training manikin, never on a person who doesn't need CPR. MedlinePlus says CPR is best done by someone trained in an accredited CPR course, and that written steps are not a substitute for that training.
In a real emergency, call first and follow the call handler's instructions rather than setting up an app.