What Is the Correct Depth Range for Chest Compressions in Adult CPR: The 5–6 cm Rule, a Two-Inch Equivalent, and the Recoil Condition That Decides Whether It Works

For an adult in cardiac arrest, the correct depth range for chest compressions is 5 to 6 centimetres, which is roughly 2 to 2.4 inches. Push at least 5 cm on every compression and don't exceed 6 cm. The lower bound is the one that saves lives; the upper bound protects the rib cage and the organs beneath it. Anyone compressing an adult chest — a nurse on a ward, a lifeguard, a parent who just called emergency services — should hold those two numbers in mind as a paired rule, because going too shallow and going too deep fail in completely different ways.

Why the Adult Depth Standard Is a Range and Not a Single Target

The 5–6 cm figure comes from the International Liaison Committee on Resuscitation, known as ILCOR, which publishes a consensus summary of resuscitation science every five years and issues interim updates between them. Its most recent consolidated adult life support guidance states that rescuers should compress the lower half of the sternum to a depth of at least 5 cm but not more than 6 cm. Regional councils — the American Heart Association in the United States, the European Resuscitation Council, and the Resuscitation Council UK — build their own guidelines on that consensus, which is why the numbers match almost word for word across the English-speaking world.

The range exists because two competing risks sit on either side of it. Too shallow, and the heart doesn't get squeezed hard enough to move blood through the coronary and cerebral circulation. Too deep, and you raise the odds of rib and sternal fractures, and in rare cases injuries to the liver, spleen, or lungs. A single target number would force rescuers to choose between those risks on every compression. A range lets them aim for the middle and stay defensible at either edge.

A third component travels with the depth rule and is just as important: full chest recoil. After each compression the chest must be allowed to return to its natural position before the next push begins. Leaning on the chest between compressions raises the pressure inside the thorax and reduces the blood that flows back into the heart, so the next compression starts from a worse position. Depth without recoil is a half-finished job.

Finally, the depth standard is specific to adults. Children and infants have their own depth rules — the paediatric guidance uses roughly one third of the chest's front-to-back diameter rather than a fixed number of centimetres — so don't carry the adult figure across to a small body. The rest of this article stays on adults, because that's where the 5–6 cm standard applies.

The Hand Position That Makes the 5–6 cm Depth Physically Possible

Depth starts with where you put your hands. Place the heel of one hand on the centre of the chest, on the lower half of the sternum, and stack the second hand on top with fingers interlocked. Keep your fingers off the ribs. Your shoulders should sit directly over your hands, and your arms should be straight, with the elbows locked. From that position, depth comes from your body weight, not from arm strength.

A rescuer kneeling on a hard floor next to a casualty on the ground has a mechanical advantage; a rescuer leaning awkwardly over a hospital bed does not. If the casualty is on a soft mattress, the mattress absorbs part of the push, and the chest may not reach 5 cm even when your technique looks correct. In that situation, get the casualty onto a firm surface or use a backboard if one is available.

The heel-of-hand placement matters for another reason: compressing over the very bottom of the sternum, the xiphoid process, concentrates force on a small, brittle structure. That's one of the routes to liver injury. Centring on the lower sternum spreads the load and gives the heart the squeeze it needs.

If you're unsure whether you're reaching depth, the practical test is your own body position. Are your shoulders stacked over your hands? Are your elbows straight? Are you letting your upper body drop rather than pushing with your arms? If the answer to any of those is no, correct the posture before you worry about centimetres.

How to Judge 5 cm Without a Ruler Mid-Compression

Nobody measures chest depth with a tape measure during a resuscitation. The workaround most training organisations teach is a felt benchmark: 5 cm is about the length of a credit card's short side, and 2 inches in imperial terms is roughly the width of two adult fingers. In practice, rescuers rely on the resistance they feel and on feedback from the chest itself. The chest should feel like it's compressing firmly and springing back, not like a soft cushion.

Mechanical feedback is now common in clinical settings. Many defibrillators and CPR feedback devices display real-time depth in centimetres and beep or prompt when the rescuer falls below the target. The ZOLL R Series and the Philips HeartStart family are two widely deployed examples; both can show compression depth on screen when paired with the right sensor or pad set. Where that equipment exists, trust the readout over your own estimate.

Training manikins are the other calibration tool. Most adult CPR manikins, including the Laerdal Resusci Anne line used in countless courses, have a clicker or depth indicator that sounds when the rescuer reaches the target. If you've practised on one, your hands have already learned the feel. Use that memory when you're on a real chest.

What you shouldn't do is guess deeper than you can control. A rescuer who pushes with everything they have, hoping to overshoot the minimum, is more likely to crack a rib than a rescuer who aims for a firm, steady 5 to 6 cm. The instinct to overdo it is understandable, but the upper bound exists for a reason.

What Happens When Compressions Are Too Shallow, and How Often That Occurs

Shallow compressions are the most common failure in real resuscitations, not the rarest. Studies of in-hospital and out-of-hospital CPR have repeatedly found that rescuers — including trained clinicians — tend to compress less deeply than the guideline recommends, especially as fatigue sets in during a prolonged attempt. The consequence is straightforward: less blood moved per compression, lower coronary perfusion pressure, and a smaller chance of a successful defibrillation.

Fatigue is the main driver. Chest compressions are physically demanding, and quality drops measurably within a couple of minutes. That's why the guidelines call for switching the person doing compressions every two minutes, ideally during the pause for a rhythm check or a defibrillator analysis. Rotating rescuers isn't a courtesy; it's a quality-control measure.

There's a second driver that's less obvious: fear of causing harm. A bystander who has never compressed a real chest may hesitate to push hard, worried about breaking ribs. The clinical reality is that rib fractures are a known and accepted risk of effective CPR, and a casualty in cardiac arrest cannot be harmed by broken ribs in the way they can be harmed by no circulation at all. Training courses address this directly because the hesitation is so common.

A third cause is surface-related. Soft surfaces, as noted, eat depth. So does a rescuer positioned at an awkward angle, such as reaching across a car seat or over the edge of a bed. Correcting the environment is often the fastest way to fix depth without changing technique.

The Upper Limit at 6 cm: Rib Fractures, Organ Injury, and the Rescuer's Worry

The 6 cm ceiling is a genuine safety boundary, not a formality. Compression beyond it raises the risk of sternal and rib fractures and, in unusual cases, injuries to the liver, spleen, or lungs. Those injuries are rare relative to the number of resuscitations performed, but they're serious when they happen, and they're the reason the guideline doesn't simply say "as deep as you can."

Rib fractures during CPR are nonetheless common even within the correct range, particularly in older casualties whose bones are more fragile. The Resuscitation Council UK and the American Heart Association both note that fractures are an expected consequence of effective compressions, and neither treats a fracture as a reason to stop or reduce depth. The calculation is that the benefit of restored circulation outweighs the harm of a broken rib in a person who is otherwise dead.

The more delicate edge case involves the xiphoid process and the upper abdomen. Compressions placed too low can drive the sternum into the liver, and compressions that combine excessive depth with a low hand position multiply that risk. That's why hand placement and depth are taught together: the right spot with the right force, or neither works.

For a rescuer, the practical rule is this. If you're on the lower half of the sternum and your shoulders are over your hands, you're unlikely to overshoot 6 cm by accident. Overshooting tends to come from a deliberate, forceful push, or from a mechanical device set incorrectly. If a feedback device is showing more than 6 cm, ease off slightly rather than ignore the reading.

What the Guidelines Actually Say, Source by Source

Different councils phrase the same rule with small variations, and it helps to know which document you're relying on. The table below sets out the wording from the major authorities. All four converge on 5–6 cm, which is strong evidence that the range is stable and not likely to move soon.

Two things stand out from that comparison. First, every council ties depth to recoil in the same sentence, which tells you the two are treated as one skill. Second, the frequency band — 100 to 120 compressions per minute — is identical across all four, so a rescuer can hold depth and rate as a single combined target.

The documents also agree on the sequencing: 30 compressions followed by 2 rescue breaths for a single rescuer with a barrier device, or continuous compressions for a bystander who isn't trained or willing to give breaths. Depth doesn't change in either mode. Neither does recoil.

If you want to check the current wording yourself, go to the source. The American Heart Association publishes its guidelines on its own site and updates them when the science changes; the European Resuscitation Council and the Resuscitation Council UK do the same. The ILCOR consensus is the upstream document that all of them cite.

Adult Depth Versus Child and Infant Depth: A Side-by-Side Comparison

The question of depth gets muddled when people carry the adult number over to a child. It shouldn't be. The paediatric rule is proportional to the body, not fixed in centimetres. The table below shows how the standards divide.

Notice that the child figure often lands close to the adult figure in absolute terms, which is where the confusion starts. A large child may need close to the adult depth; a small child less. The proportional rule handles that variation, and it's the rule to follow if you're unsure. The infant figure is smaller again because the chest is much smaller.

The mistake to avoid is applying adult depth to an infant. Compressing an infant's chest to 5 or 6 cm is far beyond one third of its depth and risks serious internal injury. If you're ever in a situation where you have to choose between an adult and a paediatric casualty, follow the paediatric rule for the paediatric casualty, even under stress.

Rate, Recoil, and Interruptions: The Conditions That Make Correct Depth Count

Depth alone doesn't produce circulation. Three companion conditions determine whether a correctly deep compression actually moves blood. The first is rate: 100 to 120 compressions per minute, which is the same speed whether you're in a hospital corridor or on a pavement. The second is recoil: the chest must come all the way back between compressions. The third is interruption discipline: every pause in compressions drops the blood pressure that's been built up, and a long pause forces the next set to rebuild it from scratch.

The guideline recommendation is to keep interruptions under 10 seconds. That covers rhythm checks, defibrillator charging, and the moment of switching rescuers. A common failure is a rescuer who pauses to talk, to reposition, or to wait for instructions while the clock runs. Every one of those seconds costs circulation.

Recoil and depth interact in a way worth spelling out. If a rescuer leans on the chest between compressions, the chest can't refill, and the next compression starts from a compressed position. The depth reading on a feedback device may still show 5 cm of travel, but the effective squeeze is less, because the chest never returned to its starting volume. That's why the guideline treats recoil as part of the depth standard rather than a separate nicety.

Put the three conditions together and you have a compact quality checklist: 5–6 cm deep, 100–120 per minute, full recoil, interruptions under 10 seconds. A rescuer who holds all four is doing high-quality CPR. A rescuer who holds only some of them is doing something less effective than they think.

Frequently Asked Questions

Is 5 cm or 6 cm the more important number to hit?

The minimum matters more for survival, while the maximum matters more for safety. Falling below 5 cm is the failure that's most common in real resuscitations and directly reduces blood flow. Exceeding 6 cm is a risk you should avoid, but it's less likely to happen by accident than undershooting. Aim for the middle of the range and treat 5 cm as a hard floor.

Can chest compressions be too deep on a frail elderly person?

Yes, in the sense that the 6 cm ceiling applies to everyone regardless of age or build. Frail casualties have more fragile ribs and a higher fracture risk even at correct depth, but the guideline doesn't lower the target for them. Broken ribs are an accepted consequence of effective CPR; a chest that isn't compressed enough doesn't circulate blood at all. Follow the same 5–6 cm rule.

Does the depth change if I'm doing compression-only CPR?

No. Compression-only CPR — continuous compressions without rescue breaths — uses the same 5–6 cm depth, the same 100–120 rate, and the same full recoil. The only thing that changes is the absence of ventilations. Bystanders who are unwilling or untrained to give breaths should still compress to the standard depth.

How does adult depth compare with child and infant depth?

Adults get a fixed 5–6 cm. Children get roughly one third of the chest's front-to-back diameter, which often works out near 5 cm but varies with the child's size. Infants get about 4 cm, again as a proportion of chest depth. Applying the adult number to an infant is a real and serious mistake because it overshoots the proportional rule by a wide margin.

What should I do if a feedback device shows I'm compressing deeper than 6 cm?

Ease off slightly on the next compressions and check your hand position. Overshooting usually comes from a deliberate forceful push or a misconfigured device, so correct the cause rather than ignoring the readout. If the device reading seems implausible — for example, it shows 10 cm when you know you're compressing gently — verify the sensor placement before trusting the number.

How quickly does compression depth degrade during a prolonged resuscitation?

Quality drops within the first couple of minutes of continuous compressions, which is why the guidelines call for rotating the compressor every two minutes. The drop is driven by fatigue and is often unnoticed by the rescuer doing the work. Rotating during a rhythm check keeps the pause short and restores depth without extending the interruption.

Is there a difference between the American two-inch figure and the metric 5 cm figure?

They're the same measurement rounded differently. Two inches equals 5.08 cm, and 2.4 inches equals roughly 6.1 cm. The American Heart Association uses the imperial phrasing for its US audience and the metric phrasing elsewhere, but the underlying standard is identical. A rescuer trained in either system is aiming at the same depth.

This article is general educational information about resuscitation technique and is not a diagnosis, treatment plan, or substitute for certified training. CPR standards are set by bodies such as ILCOR, the American Heart Association, the European Resuscitation Council, and the Resuscitation Council UK, and local protocols may add requirements. Enrol in a hands-on course with a qualified local instructor before relying on these figures in an emergency. If someone is unresponsive and not breathing normally, call your local emergency number immediately.