The SI unit for stress is the pascal (Pa), while strain is dimensionless and has no unit.
Stress is defined as the force applied per unit area. The pascal is equal to one newton per square meter (N/m²). Therefore, whenever we talk about stress in materials, we express it in pascals. For example, you might encounter stresses of thousands or millions of pascals (kPa, MPa) in engineering contexts.
On the other hand, strain measures the deformation of a material compared to its original length. Since it represents a ratio (change in length/original length), it is dimensionless. This means that strain doesn’t have its own unit and is typically expressed as a decimal number or percentage. For example, a strain of 0.01 means the material has deformed by 1% of its original length.