This tool allows you to calculate the cracking moment for a rectangular concrete section. It also calculates the neutral axis and stresses in the concrete and the steel in both cases, before and after cracking. To perform the calculation we have used the formulation proposed in the article Calculation of the neutral axis in concrete sections (in spanish) . This article shows how to calculate the neutral axis of the section once cracked. Similarly, we could calculate the neutral axis before cracking. The next image shows the state of deformations, stresses and forces of our section before and after cracking and the position of the neutral axis:
Geometrical characteristics  
Heigth (mm) (h):  
Width (mm) (b):  
Upper reinforcement (mm^2) (A2):  
Lower reinforcement (mm^2) (A1):  
Upper concrete cover (mm) (R2):  
Lower concrete cover (mm) (R1): 
Material characteristics  
Concrete compression strength (MPa) (fck):  Steel yielding limit (MPa) (fys):  
Concrete Young modulus (N/mm^2) (Ec): 
Typical value:
35000 MPa; 
Steel Young modulus (N/mm^2) (Es): 
Typical value:
210000 MPa; 
Concrete tensile strength (MPa) (fctm): 
In the explanation section, at the beginning of the tool, there is a table with the tensile strengths as a function of the compressive strengths. 
Calculate

Results just before cracking  
Cracking moment:  
Neutral axis before cracking  
Inertia before cracking  
Bottom reinforcement stress:  
Top reinforcement stress  
Compression stress in concrete produce by the cracking moment:  
Results just after cracking  
Neutral axis after cracking:  
Inertia after cracking  
Compression stress in concrete produce by the cracking moment:  
Bottom reinforcement stress:  
Top reinforcement stress 