There is no single pressure that breaks all bones, because bone type, loading direction, impact speed, contact area, and the person’s age and health all change the answer dramatically. As a raw material, the dense outer layer of a human bone can withstand roughly 8,700 to 26,000 PSI of compressive pressure before it fails, with a typical mid-range value around 18,500 PSI. But that material-level number rarely tells you what happens in real life, where a fall, a kick, or a car crash delivers force over a specific area and in a specific direction. The practical picture is more interesting and more variable than any single figure suggests.
Why PSI Alone Does Not Tell the Whole Story
PSI stands for pounds per square inch, a measure of pressure. It tells you how much force is spread over how much area. When engineers test a small cube of bone in a laboratory press, they report its ultimate compressive strength in megapascals (MPa), which is just a metric version of PSI. One MPa equals about 145 PSI. In those tests, samples of cortical bone from the femur (the thighbone) have shown compressive strengths ranging from about 60 MPa up to 180 MPa, with a median near 128 MPa, while broader literature puts the range for femoral cortical bone at roughly 100 to 191 MPa.1Scientific Reports. Computed tomography porosity and spherical indentation for determining cortical bone millimetre-scale mechanical properties Translated, that median of 128 MPa works out to about 18,500 PSI. So if you compressed a tiny, perfectly shaped block of dense thighbone, it would hold up to roughly that pressure before crumbling.
The catch is that real bones are not tiny uniform cubes under a perfectly aligned press. They are curved, hollow, and loaded in complex ways. A punch to the nose concentrates force on a thin plate of bone across a tiny area. A fall onto an outstretched hand bends the forearm bones rather than compressing them. A twisting sports injury spirals force through the tibia. In each scenario, the effective pressure at the fracture site is different even if the total force is the same. That is why researchers studying actual fractures usually report the breaking force in newtons (a unit of force) rather than PSI, and why most of the practical numbers that follow are in force rather than pressure.
Compression, Tension, Bending, and Twisting
Bone is not equally strong in every direction. It resists compression better than it resists being pulled apart (tension). Studies on both human and bovine bone consistently show that tensile yield strength is roughly 30 percent lower than compressive yield strength.2Journal of Biomechanics. Differences between the tensile and compressive strengths of bovine tibial trabecular bone depend on modulus 3PubMed Central. Insights into the effects of tensile and compressive loadings on human femur bone That gap matters because most real-world fractures involve bending or twisting, not pure compression. When a long bone bends, one side gets compressed while the opposite side gets stretched. The bone typically cracks first on the tension side, then the fracture propagates through.
Twisting creates its own fracture pattern. When tibiae are loaded in torsion until they break, the result is a characteristic spiral fracture, the kind orthopedic surgeons commonly see from skiing accidents or awkward landings.4PubMed Central. Torsional stiffness and strength of the proximal tibia are better predicted by finite element models than DXA or QCT Even small bones follow these patterns. The metatarsals in your foot, tested in torsion, failed at torques between about 1.9 and 6.9 newton-meters, with the big-toe metatarsal being the strongest of the group.5Journal of Mechanics in Medicine and Biology. MECHANICAL PROPERTIES OF THE HUMAN METATARSAL BONES
The takeaway is that asking “how much pressure breaks a bone” is a bit like asking “how much force opens a door.” It depends on whether you push near the hinge or near the handle, whether you push straight in or twist the knob. A bone loaded in its weakest direction, at the thinnest part of its cross-section, will fail at forces far lower than its compressive-strength numbers would suggest.
How Much Force Actually Breaks Specific Bones
When researchers do fracture specific bones, they usually report the force in newtons. One newton is roughly a quarter-pound of force, so you can divide by about 4.45 to get a feel for the pounds involved. Here are some real-world fracture-force ranges drawn from cadaver studies and combat-sports impact research:
- Forearm bones: Roughly 670 to 3,550 N, or about 150 to 800 pounds of force. That wide spread reflects whether the hit lands on the thin ulna or the thicker radius, and whether the bone is loaded in bending or direct impact.
- Ribs: About 1,200 to 5,900 N, or roughly 270 to 1,325 pounds. Rib geometry varies a lot from person to person, which is one reason some people crack a rib in a minor car accident while others walk away from harder impacts.
- Tibia (shinbone): Roughly 4,110 to 8,450 N, or about 925 to 1,900 pounds of force.
- Femur (thighbone): About 5,000 to 8,230 N, or roughly 1,125 to 1,850 pounds. The femur is the longest, densest bone in the body, and it takes substantial force to break it through direct impact.
These ranges come from cadaver testing and from comparing known martial-arts strike forces against documented fracture thresholds.6PubMed Central. Impact Force and Velocities for Kicking Strikes in Combat Sports: A Literature Review A well-placed roundhouse kick from a trained fighter can generate enough impact to exceed the fracture threshold of a rib or forearm, with peak forces comparable to those seen in severe motor vehicle crashes.
The Skull Is Its Own Category
The skull behaves differently from long bones because it is a curved shell rather than a tube. When researchers test human skulls to failure, the breaking force depends heavily on the region struck and on how quickly the load is applied. Under slow, steady loading, skulls fractured at an average of about 6,400 N (roughly 1,440 pounds of force). Under rapid, impact-like loading, the average jumped to about 11,900 N (around 2,675 pounds), even though the skull actually deflected less and absorbed slightly less total energy.7PubMed. Biomechanics of skull fracture That seems counterintuitive: the skull appears “stronger” when hit faster. The explanation is that at higher speeds, the bone does not have time to bend and distribute force, so the peak force rises before a crack initiates, but the skull shatters more abruptly once it does.
Regional differences matter too. The thick frontal bone above your eyebrows is far harder to crack than the thin temporal bone on the side of the head. Testing on porcine skulls (which closely resemble human skull bone in density and structure) found mean peak fracture forces near 7,760 N for lateral impacts, with individual values scattered over a wide range.8PubMed. How hard is hard enough? An investigation of the force associated with lateral blunt force trauma to the porcine cranium The nasal bones, by contrast, sit at the fragile end of the spectrum and can fracture at forces well below 1,000 N.
Impact Speed Changes Everything
Bone is not like a steel beam that has essentially the same strength whether you load it slowly or quickly. Bone is a living composite of mineral crystals embedded in a collagen matrix, and that collagen behaves like a viscoelastic material: its properties change depending on how fast you deform it. Under slow loading, collagen fibers have time to stretch and absorb energy, making bone tougher. Under rapid impact, the bone becomes stiffer and more brittle.
Simulation work on cortical bone shows that fracture toughness (a measure of how well bone resists a crack spreading once it starts) drops sharply as strain rate increases up to a certain threshold, then levels off.9PubMed Central. THE EFFECT OF STRAIN RATE ON FRACTURE TOUGHNESS OF HUMAN CORTICAL BONE: A FINITE ELEMENT STUDY In practical terms, this means a sudden impact can fracture a bone that would have survived the same total energy delivered slowly. It also means that static fracture-toughness numbers from laboratory tests can underestimate how easily a bone breaks under real-world dynamic conditions like a fall or a collision.10Materials Science and Engineering: C. Dynamic fracture of bovine bone
This is part of why car crashes are so dangerous to the skeleton. The forces involved are high, but the speed at which they are delivered is equally important. Bone that could sustain a heavy static load shatters under the same load delivered in milliseconds.
Dense Outer Bone Versus Spongy Inner Bone
Not all bone tissue is the same. The hard outer shell (cortical bone) and the porous, honeycomb-like interior (trabecular bone) have very different mechanical properties. In the femoral neck, the region just below the ball of the hip joint and one of the most common fracture sites in older adults, cortical bone tested at an apparent modulus of about 17.2 GPa and a yield stress of about 50 MPa. Trabecular bone in the same region was roughly half as stiff (8.8 GPa) and yielded at about 30 MPa. Yet trabecular bone was actually tougher, meaning it absorbed more energy per unit volume before breaking (about 3.2 MJ/m³ versus 1.6 MJ/m³ for cortical bone).11JBMR Plus. Cortical and trabecular mechanical properties in the femoral neck vary differently with changes in bone mineral density
This means bones break in different ways depending on how much of each tissue type is present at the fracture site. A region rich in trabecular bone can deform and absorb energy, potentially yielding a crumpled, compressed fracture. A region with thin cortical walls and little trabecular support may snap more cleanly. The ratio of cortical to trabecular bone shifts across your skeleton and across your lifespan, which is one reason fracture risk is not the same everywhere or at every age.
How Age Reshapes Bone Strength
Children’s bones are genuinely different from adult bones. Compared with adult tissue, children’s bone has a lower stiffness and lower bending strength but deflects more before breaking and absorbs more energy in the process.12PubMed. The mechanical properties of bone tissue in children This is why greenstick fractures, where the bone bends and cracks on one side without snapping all the way through, are characteristic of childhood injuries. A child’s bone is more like a green twig; an adult’s is more like a dry stick.
At the other end of life, aging thins cortical walls, reduces trabecular density, and changes the collagen cross-linking that gives bone its flexibility. Research on rib cortical bone found that age had a highly significant effect on the strain at which failure occurred, while sex alone did not significantly predict failure strain.13Frontiers in Bioengineering and Biotechnology. Rib Cortical Bone Fracture Risk as a Function of Age and Rib Strain: Updated Injury Prediction Using Finite Element Human Body Models In other words, the older the bone, the less it can deform before cracking, regardless of whether the person is male or female. Rib geometry, including cortical area and overall cross-sectional shape, also strongly predicts how much force a rib can handle before it breaks, which helps explain why two people of the same age can have very different vulnerability to chest injuries.14PubMed Central. Rib Geometry Explains Variation in Dynamic Structural Response: Potential Implications for Frontal Impact Fracture Risk
The Fracture Threshold and Osteoporosis
Bone mineral density, the number that shows up on a DEXA scan, is only a rough guide to fracture risk. Researchers have explored a concept called the “load-to-strength ratio,” which compares the force a fall delivers to the hip against the force the hip can actually handle. People with very low femoral strength (below about 2,000 N, or 450 pounds of force) consistently exceeded the theoretical fracture threshold during a sideways fall. But people with moderately low bone strength (between about 2,000 and 4,000 N) fell on both sides of the threshold, meaning some would fracture and some would not, depending on the specifics of the fall.15PubMed Central. Theoretical implications of the biomechanical fracture threshold Bone density alone explained only about 14 percent of the variation in that ratio, which is why doctors increasingly recognize that density scans do not capture the whole picture.
This finding has a practical implication: someone with only mildly reduced bone density (the “osteopenic” range, not yet osteoporosis) can still have a high fracture risk if their bone geometry is unfavorable or if the fall delivers force in just the wrong direction. Conversely, someone with somewhat low density but good bone architecture and thick soft tissue padding over the hip might survive the same fall without a crack.
Your Body’s Built-In Shock Absorbers
Bone does not face impacts alone. The muscle, fat, and connective tissue covering a bone absorb and distribute force before it reaches the skeleton. This is especially relevant at the hip. Hip fracture risk depends not just on bone strength but on how much of the impact force from a fall actually reaches the proximal femur, and soft tissue over the hip helps reduce that transmitted force.16PubMed. Soft tissue stiffness over the hip increases with age and its implication in hip fracture risk in older adults
Finite element simulations have quantified this effect. When the soft tissue thickness over the hip joint dropped from 26 mm to 5 mm (mimicking a very thin person), the peak force reaching the bone rose by about 38 percent, and peak strain nearly doubled.17PubMed. Effects of trochanteric soft tissue thickness and hip impact velocity on hip fracture in sideways fall through 3D finite element simulations This is one reason hip fractures are more common in very thin elderly people: less padding means more force transmitted directly to a bone that has already weakened with age. Active muscle contraction at the moment of impact also plays a role; the same bone structure and adaptation that helps the skeleton resist routine loading forces can contribute to shock absorption during a sudden event.18PubMed Central. Mechanical basis of bone strength: influence of bone material, bone structure and muscle action
Stress Fractures and Repeated Low-Level Loading
Everything discussed so far involves a single event delivering enough force to crack a bone. But bones can also fail under loads far below their single-event fracture threshold if those loads are repeated often enough without adequate recovery time. Stress fractures happen when microscopic damage from repeated submaximal loading accumulates faster than the body can repair it.19PubMed Central. Stress fractures of the foot – current evidence on management Over time, those tiny injuries coalesce into a visible crack and eventually a complete break.20PubMed. Stress fractures of the foot and ankle
The metatarsals and tibia are common sites for stress fractures in runners and military recruits, precisely because these bones absorb repetitive ground-reaction forces with every step. In these cases, no single footstrike comes anywhere near the thousands of newtons required to snap the bone outright. Instead, the cumulative effect of thousands of loading cycles at modest force levels outpaces the bone’s remodeling process. Training errors, sudden increases in mileage, poor footwear, and nutritional deficiencies that slow bone turnover all raise the risk. This is a fundamentally different failure mode from a traumatic fracture, and it is why asking “how much force breaks a bone” without specifying “in one shot or over many repetitions” leaves out half the story.
Why Animal Studies Do Not Translate Directly
If you encounter fracture-force data from animal experiments, treat it with caution. Large differences exist between species in bone density, mineral content, and mechanical competence. Of the animals commonly used in bone research, rat bone was the most different from human bone, while canine and porcine bone most closely resembled human samples. Human bone actually showed some of the lowest bone density and fracture stress values among the species tested.21PubMed. Interspecies differences in bone composition, density, and quality: potential implications for in vivo bone research That means fracture-force numbers from rat or rabbit studies consistently overestimate how much force a human bone can handle, and even pig or dog data needs adjustment. Researchers are aware of this, but popular sources sometimes cite animal numbers without flagging the species difference.
How Scientists Measure Bone Strength
Getting reliable fracture data is harder than it sounds. The most direct approach is to take a bone (usually from a cadaver) and load it in a testing machine until it breaks. Methods range from whole-bone tests, where the entire femur or tibia is loaded, down to nanoindentation, where a tiny diamond tip presses into a microscopic region of bone tissue.22PubMed Central. Methods for assessing bone quality: a review Each scale gives different information. Whole-bone tests tell you the structural strength, the force the bone as an organ can handle. Micro- and nano-scale tests tell you about material properties, the intrinsic toughness of the tissue itself. Both are useful, but they answer different questions. The material might be strong while the structure is weak (thin cortical walls, for example), or the structure might compensate for weaker material through favorable geometry.
This multi-scale reality is a big part of why there is no single PSI answer. The number you get depends on the scale at which you test, the direction you load, the speed of loading, the region of the bone, the donor’s age, and the donor’s health status. Any honest answer to the question “how much pressure does it take to break a bone” has to come with several qualifiers attached. The ranges given here are real, but they describe corridors of possibility rather than bright lines.