Grantham Sound (Spanish Bahia de Ruiz Puente) is a bay on East Falkland, Falkland Islands, which opens out into the Falkland Sound. At its landward end, it narrows about becomes Brenton Loch (sometimes included as a part of it). Mount Usborne overlooks it.

Along with San Carlos Water, it is one of the proposed East Falkland termini for the anticipated ferry to West Falkland.