The Beilinson regulator is $\frac{1}{2}$ times the Borel regulator.
The Beilinson regulator is a map from algebraic K-theory to Deligne cohomology and the above equality generalizes Borel's theorem on the algebraic K-theory of number rings, which in turn generalizes the class number formula from algebraic number theory. A complete proof is contained in this book. To get an impression of the range of involved fields one may just look at its Table of ContestsContent, from which I copy the names of chapters:
- Simplicial and Cosimplicial Objects
- H-spaces and Hopf Algebras
- The Cohomology of the General Linear Group
- Lie Algebra Cohomology and the Weil Algebra
- Group Cohomology and the van Est Isomorphism
- Small Cosimplicial Algebras
- Higher Diagonals and Differential Forms
- Borel's regulator
- Beilinson's Regulator