When there is a change in volume of the body, without any change in its shape because of a force which is applied uniformly and normally it is known as Bulk strain.
Volume strain is defined as change in volume of body per unit original volume is volume strain.
If Δv is the change in volume produced in a body of original volume V,then the formula for bulk or volume strain is given as,
Bulk or Volume strain = Change in volume / Original Volume.
Bulk or Volume strain = Δv / V
As the linear strain is ratio of lengths, it has no unit and dimension.