It is defined in DIN EN 12890 and specifies the difference in length of cast parts between casting mold and casting.
Only linear shrinkage is taken into account. It depends on the type of casting material, construction as well as the stability of the mold during solidification and shrinkage.
The difference in length must be added to the pattern dimensions as shrinkage allowance. This is applicable to all casting processes: sand casting, die casting, precision casting, pressure die casting. Any shrinkage obstacles (e.g. ribs and the like) must be taken into account for the calculation of shrinkage allowance.
If absolute accuracy is required, the thickness of the coating layer (mold coating, corecoating, die coating, see Coating) must also be taken into account. It is between 0.08 and 0.12 mm for surfaces providing contours.