The CCP4 file format is file generated by the Collaborative Computational Project Number 4 in 1979. The file format for electron density has become industry standard in X-ray crystallography and Cryo-electron microscopy where the result of the technique is a three-dimensional grid of voxels each with a value corresponding to density of electrons (see wave function) The CCP4 format is supported by almost every molecular graphics suite that supports volumetric data. The major packages include:

• Visual molecular dynamics
• PyMOL
• UCSF Chimera
• Bsoft
• Coot
• MOE