cement content per cum of concrete for M25 grade can not be the same all over world just because of following reasons;
1. Quality of the aggregates - shape, fineness, absorption, impact value, crushing value etc.
2. Type of Cement used for producing concrete - OPC, PPC, PSC etc.
3. Uses of admixture for modifying one or more properties of concrete - Plays much more important role.
4. Design and Specification Requirements.
5. there are lot more factors.
Normally in Maharashtra i had seen mixes for M25 grade concrete where admixtures are used to modify concrete properties, having cement content from 260 Kg to 350 Kg per cum.
For mixes without admixture cement content about 300 to 350 Kg per cum.