What Is the Ratio of Chest Compressions to Ventilations When Performing CPR for an Adult: The 30:2 Rule, Depth, and Speed

For an adult in cardiac arrest, the compression-to-ventilation ratio is 30 chest compressions to 2 rescue breaths. The American Heart Association and the International Liaison Committee on Resuscitation both set that 30:2 figure for one-rescuer and two-rescuer adult CPR. The exception matters just as much: once an advanced airway such as an endotracheal tube or supraglottic device is in place, compressions become continuous at 100 to 120 per minute and you give 1 breath every 6 seconds — no more pausing for a 30:2 cycle.

The 30:2 Ratio and Where the Numbers Come From

The 30:2 figure means 30 compressions followed by 2 breaths, repeated in cycles, in adult basic life support. The American Heart Association publishes this in its current Guidelines for CPR and Emergency Cardiovascular Care, and the International Liaison Committee on Resuscitation reaches the same recommendation through its Consensus on Science and Treatment Recommendations. The AHA's adult basic life support algorithm — the sequence taught on its Heartsaver and BLS provider courses — runs exactly this way. Learn one number: thirty then two. Everything else in adult CPR hangs off that loop.

Two breaths are not two full lung inflations. Each rescue breath should last about 1 second and make the chest visibly rise, then you let the chest fall before the second breath. If you give more air than that, you push extra volume into the stomach, which raises the risk of vomiting and aspiration during compressions. The AHA calls this avoiding excessive ventilation, and it's one of the most common errors even among trained responders. Over-breathing also raises pressure inside the chest, which reduces the blood your compressions just pushed forward.

The ratio assumes a single rescuer or a pair working together. With one rescuer on an adult, you perform all 30 compressions, then give 2 breaths, then resume compressions. With two rescuers, the roles stay fixed for each full cycle: one person compresses while the other prepares the pocket mask or bag-valve-mask and delivers the two breaths, then they swap at the next cycle boundary. The ratio itself never changes because a second person arrived.

The number to hold onto is the compression count, not a clock. Count 30 out loud, deliver 2 breaths, restart immediately. Don't round up to 31 or drop to 28 because you lost count — restart at 1 and keep the rhythm without pausing to figure out where you were.

Compressions Per Minute and How the Cycle Plays Out

The compression rate for adults is 100 to 120 per minute, and compressions should be at least 2 inches (5 cm) deep but no more than 2.4 inches (6 cm). Rate and depth come from the same AHA adult basic life support guidance that sets the 30:2 ratio, so they belong in the same mental checklist. Getting the ratio right while compressing too slowly is a common out-of-hospital mistake, because the depth and speed matter to circulation just as much as the count does. Aim for a rate where 30 compressions take somewhere close to 15 to 18 seconds; that lands you inside 100 to 120 per minute.

Here's how a full two-minute block actually flows, cycle by cycle:

1: Start compressions at 100 to 120 per minute, counting 1 through 30 out loud. 2: Give 2 rescue breaths, each about 1 second, watching for visible chest rise. 3: Resume compressions immediately and repeat the 30:2 loop. 4: At the end of 5 cycles — roughly 2 minutes — pause only for a rescuer swap or AED arrival, ideally in under 10 seconds.

That 5-cycle, 2-minute structure matters because most protocols time the rhythm strip analysis or AED shock around it. If you're doing 30 compressions at the low end of the rate, about 100 per minute, a full 30-compression set plus two 1-second breaths takes roughly 20 seconds. Five cycles run a little over two minutes — which is where the "swap every 2 minutes" guidance comes from. Compression quality falls off after about two minutes, so the swap keeps a fresh rescuer on the chest.

If you have an AED, keep doing compressions while the pads are applied and the machine analyzes, and pause only for the shock itself. The AHA's 2020 update to the adult basic life support algorithm emphasized minimizing those pauses. A pause for 30 to 40 seconds to let the AED fully cycle costs far more circulation than the two breaths you skipped.

One timing trap: don't time the two-minute block to the breaths. If you're a lone rescuer and need to count, count cycles, not seconds. Five cycles is a rough marker, not a stopwatch instruction. Watching the clock for exactly 2 minutes while compressions drift slower than 100 per minute does more harm than good.

When the Ratio Changes: Advanced Airways and the 6-Second Rule

Once a trained provider places an advanced airway — an endotracheal tube, a supraglottic airway, or a similar device — the 30:2 cycle ends. Compressions become continuous at 100 to 120 per minute, and ventilations go to 1 every 6 seconds, which works out to 10 breaths per minute. That's the AHA standard for adult cardiac arrest care with an advanced airway in place. The switch removes the pause for breaths, which is the whole point: continuous compressions maintain the blood pressure that's driving oxygen to the brain.

The 6-second breath interval is not a guess. Ten breaths per minute is one every 6 seconds, so the number lines up cleanly with the recommended rate. Two rescuers are required for this pattern: one person compresses without stopping, and the other watches the clock and delivers a breath on each 6-second mark. Single-rescuer CPR with an advanced airway isn't practical because nobody can do continuous compressions and time ventilation reliably at the same moment.

Don't confuse this with rescue breathing done in a non-arrest situation. If someone has a pulse but isn't breathing normally, the adult rescue-breathing rate is 1 breath every 6 seconds, or 10 per minute, and that has nothing to do with 30:2. The distinction is cardiac arrest versus respiratory arrest: no pulse means 30:2, a pulse but no breathing means rescue breaths alone. If you're unsure whether there's a pulse, the AHA guidance is to assume arrest and start compressions.

Hands-only CPR sits outside the 30:2 frame entirely. If you're untrained, unwilling to give mouth-to-mouth, or unsure of your technique, call 911 and push hard and fast in the center of the chest at 100 to 120 per minute with no breaths at all. The AHA endorses compression-only CPR for untrained bystanders precisely because it's better than nothing and keeps the person alive until trained help or a defibrillator arrives.

The Ratio Alone Won't Save Anyone: Depth, Recoil, and Pauses

A perfect 30:2 count does almost nothing if the compressions are shallow or you lean on the chest between them. Push at least 2 inches into the adult chest, and let the chest come all the way back up — full recoil — before the next compression. Leaning on the chest between compressions keeps pressure inside the chest and keeps blood from returning to the heart to be pumped again. Depth and recoil are part of the same AHA adult basic life support standard that sets the ratio, and no ratio compensates for breaking them. Don't exceed 2.4 inches of depth either.

Hand placement matters for depth. Put the heel of one hand on the center of the chest, on the lower half of the sternum, and put the other hand on top with fingers interlocked. Keep your arms straight and your shoulders directly over your hands, and let your upper body weight drive the compressions rather than your arms. If your elbows bend, you'll fatigue quickly and your depth will drift.

The single biggest failure mode in real CPR is the pause, not the count. Hands-off time — everything from fumbling for a mask to three people arguing about who's in charge — shrinks the chance of survival every second. The AHA's adult basic life support algorithm prioritizes minimizing interruptions, and the 30:2 structure exists partly to keep pauses short and predictable. Each pause to give two breaths should last only as long as the two 1-second breaths. Don't stop to discuss technique, don't stop to look for a pulse mid-cycle, and don't stop because the person grunts or moves a little — those are often reflex movements, not signs of recovery.

If compressions ever feel wrong, adjust speed or depth, never the ratio. A common instinct when the person doesn't respond is to add more breaths, which is the opposite of what the guidelines want. Two breaths per 30 compressions is fixed during the basic life support phase; more breathing is not better and actively reduces circulation.

Timing a Two-Rescuer Cycle: A Worked Calculation

Here's a concrete way to see what 30:2 costs you in time. At exactly 100 compressions per minute, each compression takes 0.6 seconds, so 30 compressions take about 18 seconds. Add two 1-second breaths with a short breath-to-breath gap of roughly half a second, and a single cycle runs about 20.5 to 21 seconds. Five cycles land near 103 seconds, slightly over the two-minute swap mark. That arithmetic is why "swap every two minutes" roughly equals "swap every five cycles" at the low end of the recommended compression rate.

Now run it at the fast end. At 120 compressions per minute, each compression takes 0.5 seconds, so 30 compressions take about 15 seconds, and the cycle drops to around 17.5 seconds. Five cycles finish in roughly 88 seconds. If you're timing to two minutes, you'll be mid-cycle when the clock hits it, so let the current cycle finish before swapping rescuers, then swap cleanly. The number that matters isn't two minutes exactly; it's that compression quality dips with fatigue, and the AHA's guidance frames the timing as approximately every 2 minutes, not a hard stopwatch rule.

What about total compressions per minute of actual arrest time? In a 30:2 cycle, the two-second breath pause means actual compression time per cycle is slightly under the theoretical per-minute rate. Over a minute at 100 compressions per minute with five or so breath pauses, you get roughly 255 to 270 compressions instead of a flat 300. That compression fraction — the share of arrest time spent actually compressing — is one of the metrics quality-improvement programs track. The 30:2 structure keeps it high, but only if the pauses stay tight.

That's the case for going hands-only if you're untrained: hands-only CPR keeps compression fraction near its theoretical maximum because there are no breath pauses at all, at the cost of no supplemental oxygen. For a bystander without a barrier device, that trade is usually worth it.

Common Mistakes With the 30:2 Count (and What to Do Instead)

One quieter mistake is swapping rescuers in the middle of a cycle. Stop at a cycle boundary — end of the two breaths — not after 17 compressions. A clean swap at a boundary takes seconds; a mid-cycle swap costs the pattern and usually a few compressions in the confusion. Another is forgetting that adults are not children: pediatric CPR uses 30:2 with one rescuer but 15:2 with two rescuers, and infants get 30:2 or 15:2 depending on the number of rescuers and the training standard. Applying 15:2 to an adult is a real error taught-correction courses catch regularly.

Adult CPR in Special Situations: Pregnancy, Drowning, and Trauma

Pregnancy is the one situation where the ratio stays the same but the setup changes. According to the American Heart Association's guidance on cardiac arrest in pregnancy, you still give 30:2 with standard high-quality compressions, but you manually displace the uterus to the left — or, more commonly now, tilt the whole patient slightly to the left — so the uterus doesn't compress the inferior vena cava. The key number for trained teams is delivery within 5 minutes of arrest if the uterus is at or above the umbilicus, because the best way to save both patient and fetus is often to deliver the baby. That 5-minute target is a maternal cardiac arrest standard, not part of the lay-rescuer ratio, and it belongs to the hospital team.

Drowning is a case where many bystanders wrongly assume breaths come first. The AHA's guidance on drowning is to start with 2 rescue breaths, then begin 30:2 cycles. The ratio is still 30:2, but the sequence opens with breaths because the arrest is usually caused by hypoxia — lack of oxygen — from submersion, so reoxygenating early makes sense. If you can't or won't give breaths, start compressions anyway.

Trauma changes the priority within the same ratio. In traumatic cardiac arrest, massive bleeding is often the underlying cause, so controlling severe hemorrhage and getting the person to definitive care takes precedence over perfect 30:2 timing, though the AHA still expects high-quality compressions at 30:2 once you've started. Hypothermia is another edge case: in cold-water or cold-weather arrest, the guidelines call for continued CPR during rewarming, and the ratio remains 30:2 throughout.

What the Ratio Is Not: Opening-Airway and Breathing Alone

The 30:2 figure only applies once you've confirmed the person is unresponsive and not breathing normally. Before compressions, you do the standard sequence: check responsiveness, call 911 or direct someone to, send for an AED, and check breathing and pulse together for no more than 10 seconds. Agonal gasps — occasional, irregular, gasping sounds — are not normal breathing and should be treated as cardiac arrest. If the person is unresponsive and not breathing normally, start compressions. If there's no AED nearby, begin 30:2 immediately.

If the person is unresponsive but breathing normally and has a pulse, you're in rescue-breathing territory, not CPR. Give 1 breath every 6 seconds, about 10 per minute, and monitor until help arrives. That's the same 6-second interval used with an advanced airway during arrest, which is why people conflate the two. The distinguishing fact is the pulse: pulse present means rescue breaths, no pulse means 30:2 compressions.

The ratio also doesn't change for age once you've treated someone as an adult. The AHA defines adult CPR as applying to anyone who has reached puberty, and once you're treating someone as an adult, 30:2 holds for one or two rescuers. For a child or infant, the ratio with two rescuers drops to 15:2. If you're unsure whether a young teenager counts as an adult for CPR purposes, treating them as adult generally leans toward more compressions, which is the safer error.

One more non-ratio: the compression-ventilation ratio is not the same thing as the compression-to-breath ratio during a rescue breath. Compressions always outnumber breaths 15 to 1 in the 30:2 cycle. The "two breaths" are a brief interruption, not a parallel activity. Don't breathe while compressing — they don't overlap.

FAQ

Is 30:2 still the correct ratio for adult CPR, or has it changed?

Yes — 30:2 remains the adult standard in the American Heart Association's current CPR and emergency cardiovascular care guidelines. The ratio has held steady since the 2005 guidelines raised it from 15:2 to 30:2 to encourage more continuous compressions. What has changed across editions is the emphasis on compression quality and minimizing interruptions, not the 30:2 number itself.

Do I give 30 compressions and 2 breaths if the person has a pulse?

No. If an adult has a pulse but isn't breathing normally, you give rescue breaths alone at 1 breath every 6 seconds, about 10 per minute — no compressions at all. Compressions on a beating heart can cause harm. If you can't find a pulse within 10 seconds or aren't sure, start 30:2.

What's the ratio if I'm doing hands-only CPR?

There is no ratio in hands-only CPR — you don't give breaths at all. A single bystander pushes hard and fast at 100 to 120 compressions per minute with full chest recoil, and calls 911 while doing it. The AHA endorses compression-only CPR for untrained or unwilling bystanders because it removes the barrier of mouth-to-mouth and keeps circulation going.

How many total compressions per minute does 30:2 actually deliver?

The theoretical maximum is 100 to 120 compressions per minute, but with the two-second breath pauses in each cycle you deliver closer to 255 to 270 compressions in a real minute at 100 per minute — roughly 85 to 90 percent of the compression-minute. That's the compression-fraction math the AHA uses when it emphasizes minimal hands-off time.

When does the ratio change to 1 breath every 6 seconds?

Only after a trained provider places an advanced airway such as an endotracheal tube or supraglottic device. At that point compressions become continuous at 100 to 120 per minute, and one rescuer gives 1 breath every 6 seconds with no 30:2 cycling. Without an advanced airway, adults stay at 30:2 even in a hospital setting.

Is the ratio the same for children and infants?

No. For children and infants, the two-rescuer ratio is 15:2, not 30:2, and the single-rescuer ratio for both is 30:2. The 15:2 figure in pediatric CPR reflects the fact that pediatric arrest is often respiratory, so breaths are more important. Applying 30:2 to a child when you're part of a two-rescuer team is a common error.

Does the 30:2 ratio change if the person vomits or the mask doesn't seal?

No. Stick with 30:2 and manage the obstacle. If the person vomits, roll them to the side briefly, clear the airway, and resume compressions immediately — keep that roll brief. If the mask or barrier won't seal, go to hands-only compressions rather than pausing to fix the device. Stopping compressions to troubleshoot costs circulation.

What's the correct ratio if I'm doing rescue breathing only during a drowning?

Drowning arrest still uses 30:2, but the AHA guidance is to start with 2 rescue breaths before the first compression — because drowning arrest is usually hypoxia-driven. That opening two breaths is separate from the 30:2 cycle; once compressions start, you return to the standard 30 compressions to 2 breaths.

This article is general educational information about CPR ratios, not a diagnosis, treatment plan, or substitute for a certified course. Guidelines can vary by country and by year, so check the current American Heart Association, International Liaison Committee on Resuscitation, or your national resuscitation council's guidance before relying on any detail here, and take a hands-on CPR and first aid course from a qualified local training provider. If you witness someone collapse or suspect a cardiac arrest, call your local emergency number immediately and follow the dispatcher's CPR instructions while help is on the way.