Tensile strength is the maximum pulling (tensile) stress a material can withstand before it breaks. It’s expressed as force divided by the original cross-sectional area — Tensile Strength (σ) = F_max / A₀ — and is typically reported in MPa, psi, or ksi. A higher number means the material resists more pulling force per unit of area before failing.
The Formula
The basic relationship behind every tensile strength number:
Tensile Strength (σ) = Maximum Force (F_max) ÷ Original Cross-Sectional Area (A₀)
This is the stress the material carries at the exact moment before it snaps or fractures under a pulling load. The area used is the original cross-section, measured before the test started — not the narrower area the material may have necked down to right before breaking. For the full walk-through of how to measure or calculate this number from scratch (test setup, worked example, applicable standards), see How to Calculate Tensile Strength — this article covers the definition, not the test procedure.
The Three Points on the Curve People Mix Up
“Tensile strength” gets used loosely, but a stress-strain curve actually has three distinct points that get lumped together in casual conversation:
- Yield strength — the stress at which the material stops behaving elastically (it would spring back to its original shape below this point) and starts permanently deforming.
- Ultimate tensile strength (UTS) — the single highest point on the stress-strain curve. When someone says “the tensile strength of this material is X,” they almost always mean this number.
- Breaking/fracture strength — the stress at the moment the material actually separates. In ductile materials, this is usually lower than UTS, because the material necks down (narrows) after passing UTS, and the engineering stress calculation (which still divides by the original area) drops even as the material is still carrying load right up to failure.
So a stress-strain curve for a ductile metal typically rises to yield, keeps rising (with the material now permanently deforming) to a peak at UTS, then drops slightly to the fracture point as the specimen necks and separates. When this article — or anyone else — says “tensile strength” without qualification, they mean UTS. If you need the calculation itself, the method is identical for UTS and general tensile strength; see the methodology article linked above.
Units and Conversions
Tensile strength is a stress value (force per unit area), so it uses stress units:
| Unit | System | Notes |
|---|---|---|
| Pa (pascal) | SI base unit | 1 Pa = 1 N/m² — rarely used directly, too small for structural materials |
| MPa (megapascal) | SI, most common in engineering | 1 MPa = 1 N/mm² |
| GPa (gigapascal) | SI, high-strength materials | 1 GPa = 1,000 MPa |
| psi (pounds per square inch) | US customary | Common on US material spec sheets |
| ksi (kilopounds per square inch) | US customary | 1 ksi = 1,000 psi |
Quick conversions: 1 MPa ≈ 145 psi, and 1 GPa ≈ 145,000 psi. If you’re comparing a metric spec sheet to a US one, converting to a common unit first avoids the easy mistake of assuming two numbers that look similar (say, “500” MPa vs. “500” psi) are the same magnitude — they’re off by a factor of roughly 145.
Typical Tensile Strength by Material (Reference Only)
These figures come from a single source in our research and are not cross-verified against independent testing data — treat them as a rough sense of scale, not a spec you’d design against:
| Material | Approximate Tensile Strength |
|---|---|
| Concrete | 2–5 MPa (weak in tension — this is why concrete is reinforced with steel rebar, which carries the tensile load concrete can’t) |
| Structural steel | 400–550 MPa |
| Kevlar | ~3,100 MPa |
| Carbon fiber | 3,500–4,100 MPa |
If you need actual engineering-grade numbers for a specific steel grade, What Is the Tensile Strength of Steel? has a per-grade reference table built from numbers that were cross-checked across multiple independent sources — those are more reliable than the single-source figures above.
Why This Matters in Practice
Tensile strength tells you the ceiling — the load at which a part fails outright. It doesn’t tell you the load at which a part starts permanently deforming (that’s yield strength, usually the number you actually design to with a safety margin), and it doesn’t tell you how a part behaves under repeated or moving loads over time (that’s a fatigue/dynamic-load question, not a tensile-strength question — see Static Load vs. Dynamic Load if that’s what you’re actually trying to evaluate). Treating “tensile strength” as the number to design against, rather than yield strength with an appropriate safety factor, is a common and avoidable mistake.
Related reading: How to Calculate, Measure, and Test Tensile Strength · What Is the Tensile Strength of Steel? · Static Load vs. Dynamic Load
