Human Bone Is Stronger Than Steel (By Weight)

Your skeleton is performing an engineering miracle right now. Human bone, when compared pound-for-pound with steel, is approximately five times stronger. This doesn't mean you can deflect bullets—it means bone achieves extraordinary strength while remaining incredibly lightweight.

The secret lies in strength-to-weight ratio, a measurement engineers obsess over when designing everything from aircraft to skyscrapers. Steel has a density of about 7,850 kg/m³, while cortical bone (the dense outer layer) ranges from just 1,300 to 2,000 kg/m³. A steel bar the same size as your femur would weigh three to five times more.

The Numbers Behind the Strength

In absolute terms, steel wins the strength contest. High-quality steel can handle tensile forces of 400 to 2,000 MPa (megapascals), while bone maxes out around 130-135 MPa. But here's where bone shows off: it achieves that impressive strength at a fraction of the weight, making it far more efficient for carrying around inside a living body.

Your femur—the thigh bone—demonstrates this engineering brilliance best. It can support compressive forces of about 205 MPa along its length, enough to handle impacts from running and jumping while keeping your total skeleton weight at just 15% of your body mass.

Why Evolution Chose Bone Over Metal

Beyond the weight advantage, bone has tricks steel can never match:

• Self-repair: Fractures heal. Bent steel stays bent.
• Adaptive remodeling: Bone strengthens where you need it most, responding to stress patterns
• Composite structure: Bone combines hard minerals with flexible collagen fibers, giving it both rigidity and shock absorption
• Directional strength: Bone is stronger along its length where forces naturally occur

This composite design gives bone a fracture toughness of about 1.5 kJ/m²—comparable to steel at low temperatures, despite bone being classified as a brittle material. The collagen fibers woven through the mineral matrix act like rebar in concrete, preventing catastrophic shattering.

The Trade-Off

There's no such thing as a perfect material. While bone excels at supporting your body weight efficiently, it's not ideal for building bridges. Steel's higher absolute strength and consistency make it better for structures that can't afford to be lightweight. And unlike bone, steel doesn't need a blood supply, calcium, or vitamin D to maintain its strength.

But for biological engineering? Bone is hard to beat. It's strong enough to handle extreme forces, light enough to move efficiently, and smart enough to heal itself. Try getting steel to do that.