We construct a partial compactification of the moduli space, M k \mathcal {M}_k , of S U ( 2 ) \mathrm {SU}(2) magnetic monopoles on R 3 \mathbb {R}^3 , wherein monopoles of charge k k decompose into widely separated ‘monopole clusters’ of lower charge going off to infinity at comparable rates. The hyperKähler metric on M k \mathcal {M}_k has a complete asymptotic expansion up to the boundary, the leading term of which generalizes the asymptotic metric discovered by Bielawski, Gibbons and Manton when each lower charge is 1.