Although partial melt in the asthenosphere is important geodynamically, geophysical constraints on its abundance remain ambiguous. We use a database of seamounts detected using satellite altimetry to constrain the temporal history of erupted asthenospheric melt. We find that intraplate volcanism on young seafloor (<60 Ma) equates to a ~20 m thick layer spread across the seafloor. If these seamounts tap partial melt within a ~20 km thick layer beneath the ridge flanks, they indicate extraction of an average melt fraction of ~0.1%. If they source thinner layers or more laterally restricted domains, larger melt fractions are required. Increased seamount volumes for older lithosphere suggest either more active ridge flank volcanism during the Cretaceous or additional recent melt eruption on older seafloor. Pacific basin age constraints suggest that both processes are important. Our results indicate that small volumes of partial melt may be prevalent in the upper asthenosphere across ocean basins.