When performing CPR you should aim to give 30 compressions at a rate of 100–120 compressions per minute, delivered at least 2 inches deep in an adult and allowing full chest recoil between each push. That 30:2 ratio applies to single-rescuer adult CPR; two-rescuer adult and pediatric CPR shifts toward 15:2, and high-quality bystander CPR may omit breaths entirely with compression-only technique.
The rate range is not arbitrary. Every number in that answer — the count, the frequency, the depth — maps onto a specific physiological problem the body faces once circulation stops. Understanding those mechanisms is what separates a rescuer who hits the target from one who drifts to 80 pushes a minute and wonders why the patient never wakes up.
How interrupted flow resets the clock
Cardiac arrest halts forward flow, but the blood already in the arterial tree keeps oxygenating tissue for a short window. Once that residual oxygen is consumed, every second without compressions deepens the oxygen debt in the brain and heart muscle. Compressions function as a manual pump: they raise intrathoracic pressure and squeeze the heart between the sternum and spine, generating a pressure gradient that pushes blood into the aorta and pulmonary arteries.
The gradient is fragile. It collapses the moment compressions stop. During the recoil phase, negative intrathoracic pressure pulls venous blood back into the chest, refilling the pump. If a rescuer leans on the chest between compressions, the chest cannot fully expand, venous return drops, and the next compression ejects less blood. This is why full recoil appears in every guideline alongside rate and depth.
The 30:2 ratio exists to balance two competing demands. Breaths resupply oxygen, but each pause for ventilation drops the perfusion pressure built up by compressions. At 30:2, the pause is short enough that aortic pressure does not fully decay before compressions resume. Professional caveat: in the first several minutes of adult sudden collapse, the blood is still well oxygenated, which is why compression-only CPR performs comparably to conventional CPR in that specific scenario (American Heart Association, 2020 guidelines).
The physiology of 100–120 compressions per minute
Below roughly 100 compressions per minute, cardiac output falls short of what the brain needs to avoid ischemic injury. Above roughly 120, a different failure mode appears: the chest wall does not have time to recoil fully, so each compression starts from a partially compressed baseline. Stroke volume per push shrinks, and total output paradoxically declines.
The 100–120 band is therefore a corridor, not a target to exceed. Studies of real resuscitations consistently show that rescuers without feedback drift slower than they think — often into the 80s and 90s — because the mental effort of counting competes with the physical effort of pushing. Professional rescuers using metronomes or feedback devices cluster inside the band; untrained bystanders frequently fall below it.
The counterintuitive detail: pushing faster is not safer. Exceeding 120 compressions per minute is associated with inadequate depth, because rescuers trade depth for speed when they fatigue. Rate and depth are coupled, and the band protects both.
Depth, recoil, and the numbers that travel together
Depth targets scale by age, and the thresholds differ enough that mixing them up is a common error:
| Patient | Compression depth | Ratio (single rescuer) | Rate |
|---|---|---|---|
| Adult | At least 2 in (5 cm), not more than 2.4 in | 30:2 | 100–120/min |
| Child (puberty onset or earlier) | About one-third of chest depth, roughly 2 in | 30:2 (15:2 with two rescuers) | 100–120/min |
| Infant (under 1 year) | About one-third of chest depth, roughly 1.5 in | 30:2 (15:2 with two rescuers) | 100–120/min |
| Adult, compression-only | At least 2 in | Continuous, no breaths | 100–120/min |
| Two-rescuer adult | At least 2 in | 30:2 | 100–120/min |
| High-quality CPR with feedback device | Target depth | Per protocol | 100–120/min |
The rate is identical across all rows. Only the count, the depth, and the breath pattern change. That consistency is deliberate: the 100–120 band is a property of human chest mechanics and perfusion physics, not of patient size.
Timing the switch and the two-minute rule
Compression quality decays with fatigue, and the decay is measurable. Rescuers who switch roles every two minutes sustain better depth and rate than those who push longer. The two-minute interval also aligns with the rhythm-analysis cycle on an automated external defibrillator, so the switch happens during a planned pause rather than mid-compression.
| Elapsed time | Action | Quality threshold |
|---|---|---|
| 0–10 seconds | Confirm unresponsiveness and breathing | No more than 10 seconds to check |
| 10–30 seconds | Call for help, retrieve AED | Begin compressions if alone |
| 0–2 minutes | First compression cycle | Depth at least 2 in, rate 100–120 |
| 2 minutes | Switch compressors, AED analysis | Pause under 10 seconds |
| 2–4 minutes | Second cycle | Same depth and rate targets |
| Every 2 minutes thereafter | Rotate compressor | Fatigue-driven decline prevented |
| After AED shock | Resume compressions immediately | No pulse check before resuming |
The professional caveat here: the two-minute rotation is a ceiling, not a recommendation to push exactly to it. If a compressor reports fatigue at 90 seconds, switch then. Depth loss begins before the rescuer consciously notices it.
Where the ratio rules collide
The 30:2 ratio has exceptions that trip up rescuers trained on a single protocol. Two-rescuer pediatric CPR uses 15:2 because children desaturate faster and benefit from more frequent ventilation. Once a child reaches puberty — judged by secondary sex characteristics, not a fixed age — the adult 30:2 ratio applies.
Airway management changes the count entirely. Once an advanced airway is placed, compressions become continuous at 100–120 per minute with one breath every six seconds, and the 30:2 cycle stops. Bystanders never face this scenario, but it explains why protocol questions on exams produce different answers depending on the assumed setting.
Red-flag warnings:
Do not delay compressions to search for a pulse if you are untrained; agonal gasping is not normal breathing. Do not stop compressions to check for a pulse unless the patient shows clear signs of life or an AED prompts you. Do not exceed 2.4 inches of depth in adults; excessive depth causes organ injury without improving output. Do not lean on the chest between compressions; full recoil is part of the target, not an afterthought. Do not interrupt compressions for more than 10 seconds for any reason short of AED analysis or moving the patient.
Misconceptions that cost depth and rate
The most persistent myth is that rescue breaths must be large. Overventilation raises intrathoracic pressure, which impedes venous return and reduces the blood available for the next compression. Breaths should be just enough to make the chest rise, delivered over about one second.
A second misconception treats the rate as a speed contest. Rescuers who push at 140 per minute often believe they are doing superior CPR; feedback data shows they are typically achieving shallower depth. The band exists because faster and deeper cannot be sustained simultaneously by most rescuers.
A third misconception confuses "hands-only" with "no technique." Compression-only CPR still requires the full depth and rate targets; skipping breaths removes the ventilation pause, not the mechanical standard. The counterintuitive corollary: compression-only CPR can actually produce better perfusion pressure in the first minutes precisely because it eliminates the pause, which is why it is a legitimate option for untrained bystanders facing adult sudden collapse.
Translating the target into action
Concrete steps for hitting 100–120 and the depth target:
Position the heel of one hand on the center of the chest, lower half of the sternum, with the second hand stacked and fingers interlocked. Keep arms straight and shoulders directly over the hands; use body weight rather than arm strength to reach depth. Push to at least 2 inches in an adult, then let the chest come all the way back up before the next push. Count aloud or use a metronome app set to 100–120 beats per minute; the Bee Gees' "Stayin' Alive" sits near 103 beats per minute and is a widely used mnemonic. Deliver 30 compressions, then two breaths of about one second each if trained and willing, then resume immediately. Rotate compressors every two minutes or sooner if depth starts to fade.
For untrained bystanders, the practical threshold is simpler: call emergency services, start hard and fast compressions in the center of the chest, and keep going until help arrives or an AED is ready. The dispatcher can coach the rate.
What the numbers cannot promise
The 100–120 rate and 2-inch depth targets improve the odds of return of spontaneous circulation, but they do not guarantee it. Survival after out-of-hospital cardiac arrest depends heavily on time to first compression, time to defibrillation, and the underlying cause of arrest. Bystander CPR roughly doubles survival in many registries, yet absolute survival rates remain low even with perfect technique.
The targets also assume a normal chest wall. Rib fractures, chest deformity, obesity, and advanced age change how depth translates into cardiac compression, and rescuers cannot measure depth precisely without a feedback device. The guidelines set a floor and a ceiling because precision is impossible in the field; the band is a practical compromise, not a physiological constant.
Finally, guideline numbers evolve. The current 100–120 band and 30:2 ratio reflect the 2020 American Heart Association consensus, and future revisions may adjust the upper rate limit or the depth ceiling as feedback-device data accumulates. Rescuers should treat the numbers as current best practice rather than permanent physics.
This article is general educational information about CPR mechanics, not a diagnosis, treatment plan, or substitute for certified training. It does not promise any outcome from performing CPR. For hands-on instruction and current local protocols, complete a course from a recognized training organization such as the American Heart Association or American Red Cross, and in an emergency call your local emergency number immediately.