# What is Flexural Strength?
**Flexural strength (also called bending strength or modulus of rupture) is the maximum stress a material can sustain at its outermost fibre when subjected to bending before it fractures or yields. It is a critical mechanical property used in construction to determine whether beams, slabs, and other structural elements can safely resist the loads applied to them.**
## How flexural strength is measured
Flexural strength is determined through standardised laboratory tests in which a specimen is loaded until failure:
### Three-point bending test
A simply supported beam specimen is loaded at its midpoint. The maximum stress at failure is calculated from the applied force, span length, and cross-sectional dimensions.
### Four-point bending test
The specimen is loaded at two symmetrical points, creating a zone of pure bending between them. This method provides a more uniform stress distribution and is often preferred for brittle materials like concrete.
## Typical values in construction
| Material | Flexural strength (MPa) |
|———-|————————|
| Normal concrete (C30/37) | 3.5–5.0 |
| Timber (softwood) | 30–50 |
| Structural steel | 250–400 (yield) |
| Clay brick | 1.5–5.0 |
| Glass | 30–100 |
## Relationship to other properties
Flexural strength differs from tensile and compressive strength. For concrete, flexural strength is typically 10–15% of compressive strength. The difference arises because bending creates both tension and compression simultaneously across the cross-section.
## Applications
– Designing reinforced concrete beams and floor slabs
– Specifying concrete pavement thickness for roads and airfields
– Selecting timber grades for structural use
– Quality control testing of precast concrete elements
– Assessing masonry and natural stone for lintels and cladding
## Related terms
– Compressive strength
– Tensile strength
– Modulus of elasticity
– Moment of resistance
– Bending moment
Want to learn more about construction terms? Visit our [knowledge base at fredsdiyplans.com](https://fredsdiyplans.com).