At Which Depth Should You Perform Chest Compressions During High-Quality Adult CPR: The 5–6 cm Rule and the Physiology Behind It

You should compress the adult chest to a depth of at least 2 inches (5 cm) but no more than 2.4 inches (6 cm). This target applies to every compression in high-quality adult CPR, whether you are a single rescuer or part of a team. Depth is measured from the sternum's resting position to its lowest point during each push.

Getting depth right matters because too shallow fails to move blood, and too deep raises injury risk without proven benefit. This explainer covers the mechanics, the numbers behind the range, the edge cases, and the practical steps that keep you inside the window.

Why Compression Depth Governs Blood Flow

The heart sits in the middle of the chest, between the sternum and the spine. Squeezing the sternum downward compresses the ventricles directly and raises intrathoracic pressure. Both actions push blood into the aorta and pulmonary arteries.

Stroke volume tracks how far the sternum travels. A deeper compression squeezes the ventricles more completely and produces a larger pressure gradient. That gradient drives blood through the coronary arteries and toward the brain.

Two mechanisms work together. The cardiac pump model credits direct ventricular squeeze. The thoracic pump model credits pressure waves inside the chest. Real CPR blends both, and both scale with depth.

Blood pressure during CPR is low even at ideal depth. Invasive monitoring in cardiac arrest patients shows systolic pressures typically in the 60–80 mmHg range during compressions. This is barely enough to perfuse a brain.

The margin between adequate and inadequate flow is thin. That is why the guidelines treat depth as a hard target rather than a suggestion.

What the Numbers Say About the 5–6 cm Window

The 2015 guideline update set the adult target at 5 to 6 cm. The 2020 and 2025 updates kept that range without change. The science behind it comes from dose-response studies and injury data.

Compression depth associates with survival in a graded way. Large registry studies show better outcomes as depth rises toward 5 cm. The curve flattens and then reverses when depths exceed roughly 6 cm.

Too shallow means poor stroke volume. A compression of 3–4 cm may generate less than half the forward flow of a full-depth compression. Rescuers routinely underestimate their own depth without feedback.

Too deep means structural injury. Autopsy series in CPR patients show rib fractures in a large share of cases and sternal fractures in a smaller share. Deep compressions cluster with liver and spleen lacerations.

Dose-response and injury data converge on the same window. That convergence is why the range is stated as a lower and upper bound rather than a single number.

Reconciling the Thresholds You Will Hear

Different sources quote different numbers, which confuses trainees. The table below places the thresholds side by side so the relationships are explicit.

The adult, child, and infant thresholds are different because chest size differs. A single adult number should not be applied to a small child.

Guideline documents express depth in centimeters first and inches second. Converting 5 cm gives 1.97 inches, which rounds to 2 inches. Converting 6 cm gives 2.36 inches, which rounds to 2.4 inches.

Metric and US units therefore describe the same physical range. Any apparent conflict between "2 inches" and "5 cm" is rounding, not disagreement.

The reconciliation rule is simple. Aim for 5 to 6 cm, treat under 5 cm as a correctable error, and avoid pushing past 6 cm on purpose.

The Time Course of a High-Quality Compression Cycle

Depth is one variable in a cycle that repeats about 100 to 120 times per minute. The timeline below maps the phases of a single compression and the surrounding rhythm.

Each compression occupies roughly half a second at a rate of 120 per minute. The downstroke and upstroke split that time. A full recoil needs the chest to return to its starting height before the next push.

Fatigue erodes depth before it erodes rate. Rescuers often keep the correct cadence while pushing shallower. That is why the two-minute rotation exists.

The cycle view explains a common failure. A rescuer who leans on the chest between compressions never allows full recoil. The next compression then starts from a lower point and delivers less travel.

Edge Cases Where Depth Needs Adjustment

Most adults receive the standard 5 to 6 cm target. A few situations change how you apply it without changing the target itself.

Older adults with osteoporosis fracture ribs more easily. That is an accepted cost of effective CPR. A fractured rib does not justify reducing depth in an adult who needs resuscitation.

Patients with obesity may need more force to reach 5 cm. The target depth stays the same, but the rescuer must generate higher force. Switching rescuers sooner helps.

Patients with a sternotomy or recent chest surgery present a judgment call. Standard compressions still apply in cardiac arrest, because survival outweighs wound disruption.

Pregnant patients in cardiac arrest receive standard depth at the usual hand position. The change is logistical, with uterine displacement and early delivery planning.

Mechanical CPR devices deliver consistent depth by design. Human rescuers vary more, and feedback devices show that variation in real time.

Misconceptions That Degrade Compression Quality

Several beliefs push rescuers off target. Each one has a measurable cost.

Pressing "hard enough to break ribs" is not the goal. The goal is 5 to 6 cm. Rib fracture is a common side effect, not a target.

Leaning on the chest between compressions feels efficient. It prevents full recoil and reduces the next stroke volume.

Faster compressions do not compensate for shallow depth. Rate above 120 per minute shortens the upstroke and correlates with shallower pushes.

A single rescuer should not power through fatigue. Depth falls quietly while the rescuer believes technique is intact.

Hand position matters less than depth for flow, but it matters for injury. Hands on the lower half of the sternum reduce liver injury compared with a low placement.

Red Flags to Correct Immediately

Depth under 5 cm on a feedback device or by direct observation. Depth over 6 cm with no corresponding outcome benefit. Incomplete chest recoil caused by leaning. Any pause longer than 10 seconds during compressions. Rate outside 100 to 120 per minute. Rescuer fatigue that visibly reduces depth.

Practical Actions That Keep Depth on Target

Depth is trainable with simple feedback and a short checklist.

Place the heel of one hand on the lower half of the sternum, with the second hand on top and fingers interlocked. Keep arms straight and shoulders over the hands.

Push down 5 to 6 cm at 100 to 120 compressions per minute. Allow the chest to return fully before the next compression.

Use a metronome or feedback device when available. These tools convert depth and rate into live numbers you can correct against.

Rotate rescuers about every two minutes, or sooner if depth visibly drops. Swapping during the rhythm check avoids extra pauses.

Rehearse on a manikin with depth display before you need the skill. Manikin practice builds the force calibration that real arrests demand.

Counterintuitive Caveat and Limits of the Evidence

The most counterintuitive finding in the depth literature is that deeper is not always better. Outcome curves rise to about 5 cm and then flatten. Pushing past 6 cm adds injury without adding survival.

A second caveat concerns measurement itself. Most depth evidence comes from feedback devices and registry data rather than randomized trials. These designs cannot fully separate depth from rescuer skill and patient factors.

Guideline targets are population-level recommendations. Individual anatomy varies, and a rigid 6 cm ceiling is a safety boundary rather than a physiologic optimum.

What the evidence supports is clear. Aim for 5 to 6 cm, correct shallow compressions first, and avoid deliberate over-compression. What it does not support is a single perfect number for every patient.

This article is general educational information, not a diagnosis, treatment plan, or substitute for certified training. CPR outcomes depend on many factors beyond depth, and no technique guarantees survival. For immediate danger, call local emergency services and follow dispatcher instructions; take a hands-on course from a qualified local instructor before relying on these skills.