What Is the Ratio of Chest Compressions to Ventilations When Performing CPR for an Adult? A 30:2 Compression-to-Ventilation Ratio Explained

The ratio of chest compressions to ventilations for adult CPR is 30 compressions to 2 ventilations (30:2) for a single rescuer or any rescuer without an advanced airway. With an advanced airway in place, ventilations become continuous at 1 breath every 6 seconds, and compressions continue uninterrupted at 100–120 per minute. The 30:2 ratio applies to adults and is taught by the American Heart Association as the standard for conventional CPR.

Why the ratio is 30:2: the physiology behind the number

The 30:2 ratio is a compromise between two competing goals: restoring circulation and restoring oxygenation. Chest compressions generate a fraction of normal cardiac output, typically 20–30 percent. That limited flow is enough to keep the brain and heart viable for a short window, but it must run almost continuously to matter. Every interruption in compressions drops coronary perfusion pressure, and that pressure takes several compressions to rebuild.

Ventilations, meanwhile, exist to reverse hypoxia, which is a common cause of cardiac arrest. But positive-pressure breaths also raise intrathoracic pressure, which impedes venous return to the heart. Too many breaths, or breaths delivered too forcefully, reduce the blood that compressions can push forward. The 30:2 ratio balances these effects: enough compressions to sustain circulation and a small, controlled number of breaths to maintain oxygenation.

The underlying arithmetic matters. At 30:2, a single rescuer delivers two breaths in roughly 10 seconds, which is the maximum acceptable interruption. That keeps the "no-flow" fraction of resuscitation time low. In plain terms, the ratio is designed so that hands leave the chest as briefly as possible.

Quantified context: rates, depths, and fractions

The ratio does not stand alone. It sits inside a set of numeric targets that only work together. Compressions should run at 100–120 per minute, at least 2 inches (5 cm) deep, with full recoil after each compression. Ventilations should each take about 1 second and deliver just enough volume to make the chest rise visibly, roughly 500–600 mL in adult CPR.

The 30:2 cycle means one rescuer completes about 5 cycles every 2 minutes before switching. That two-minute mark is not arbitrary: high-quality compressions degrade measurably around that point as fatigue sets in. The 2020 AHA guidelines also specify a chest compression fraction above 60 percent, with a practical target of 80 percent or higher. The ratio directly serves that fraction by limiting breath-related pauses.

Edge cases: when the 30:2 ratio does not apply

The ratio changes the moment an advanced airway is placed. Once a supraglottic airway or endotracheal tube is secured, the AHA recommends continuous compressions with 1 breath every 6 seconds, which equals 10 breaths per minute, delivered without pausing compressions. The 30:2 ratio is suspended entirely in that setting because the airway protects ventilation and interruptions no longer serve a purpose.

Several other situations alter the calculation. If the rescuer is unwilling or unable to deliver mouth-to-mouth breaths, hands-only CPR (compressions alone) is appropriate for adult out-of-hospital arrest, and the AHA endorses it for untrained or reluctant bystanders. For a child or infant with one rescuer, the ratio is 30:2; with two trained rescuers, it shifts to 15:2. For a newborn, the ratio is 3:1. These ratios differ because pediatric and neonatal arrest more often stems from hypoxia, so ventilation carries relatively more weight.

A counterintuitive professional caveat: more ventilation is not better. Hyperventilation during CPR is a recognized and harmful error. It raises intrathoracic pressure, reduces venous return, and can lower survival. The 30:2 ratio is a ceiling on breaths, not a target to exceed.

Deliver each breath over about 1 second and watch for chest rise. Avoid rapid or forceful breaths; they increase intrathoracic pressure. Do not pause compressions more than 10 seconds to give breaths. Switch compressors every 2 minutes, ideally during the rhythm check. Do not lean on the chest between compressions; allow full recoil.

Common misconceptions about the compression-to-ventilation ratio

The most persistent misconception is that the ratio is always 30:2 in every cardiac arrest. It is not. The ratio is setting-dependent: rescuer count, patient age, and airway status all change it, as the table below shows.

Another misconception is that two breaths must fully inflate the lungs. In adult CPR, the goal is visible chest rise, not maximal volume. Overinflation is a common error among lay rescuers and even some clinicians, and it undermines the hemodynamics the compressions are trying to preserve.

A third misconception is that hands-only CPR is inferior CPR. For adult out-of-hospital cardiac arrest, particularly when the cause is cardiac, hands-only CPR produces survival outcomes comparable to conventional CPR in many studies, and it removes the barrier of mouth-to-mouth that stops bystanders from acting. Conventional 30:2 CPR remains the standard for trained rescuers and for arrests with a likely hypoxic cause.

One more misconception deserves a direct correction: the ratio is not a substitute for depth and rate. A rescuer who hits 30:2 perfectly but compresses at 80 per minute or 1 inch deep is delivering poor CPR. The ratio is one variable among several, and the AHA quality metrics weight depth, rate, recoil, and compression fraction heavily.

Practical actions: applying the ratio correctly

The practical sequence for adult CPR begins with recognizing arrest: unresponsive, not breathing normally, or only gasping. Call emergency services or direct someone to call, and send another person for an AED. Then begin compressions immediately.

For a single rescuer with no advanced airway, the cycle is straightforward. Give 30 compressions at 100–120 per minute, then 2 rescue breaths, each over about 1 second. Repeat without interruption except for AED analysis or a rhythm check. Switch rescuers every 2 minutes or sooner if quality declines. When a second trained rescuer arrives, they can take over ventilations while the first continues compressions, but the 30:2 ratio remains until an advanced airway is placed.

For a rescuer who cannot or will not ventilate, hands-only CPR is the correct fallback: compress continuously at 100–120 per minute. The moment an advanced airway is secured by a trained provider, switch to continuous compressions with 1 breath every 6 seconds and stop pausing for breaths.

The practical thresholds to memorize are these: 30 compressions, 2 breaths, 100–120 per minute, at least 2 inches deep, full recoil, switch every 2 minutes, pause no more than 10 seconds per breath cycle.

Limitations: what the ratio cannot tell you

The 30:2 ratio is a guideline-derived standard, not a patient-specific prescription, and it cannot capture every variable in a real arrest. Survival from out-of-hospital cardiac arrest remains low, and the ratio itself is only one contributor among many, including time to CPR, time to defibrillation, cause of arrest, and bystander training rates. No ratio guarantees an outcome.

Evidence also has gaps. Much of the ratio's support comes from physiologic modeling and observational data rather than large randomized trials comparing ratios head to head in adults, and guideline bodies update recommendations as evidence accumulates. The 2020 AHA guidelines remain the current reference point for adult CPR in the United States, but readers should confirm against the most recent published guidelines, since recommendations are periodically revised.

Finally, this ratio applies to conventional CPR performed by a rescuer. Mechanical CPR devices, extracorporeal CPR, and in-hospital protocols may specify different parameters. The number 30:2 is the right answer to the question as asked, but it is one piece of a larger system of resuscitation care.

This article is general educational information about CPR guidelines, not a diagnosis, treatment plan, or substitute for certified training. It does not promise any outcome. For hands-on instruction and current certification, consult a qualified CPR training organization or local emergency medical services; in an actual emergency, call local emergency services immediately.